THE UNIVERSITY OF TEXAS BULLETIN No.3113: April 1, 1931 THE NATURAL REGIONS OF TEXAS By ELMER H. JOHNSON Industrial Geographer Bureau of Business Research Research Monograph No. 8 PUBLISHED BY THE UNIVERSITY OF TEXAS AUSTIN Publications of The University of Texas Publications Committees: GENERAL: FREDERIC DUNCALF MRS. C. M. PERRY J. F. DOBIE C.H. SLOVER J. L. HENDERSON G. W. STUMBERG H.J. MULLER A. P. WINSTON OFFICIAL: E. J. MATHEWS KILLIS CAMPBELL C. F. ARROWOOD C. D. SIMMONS E. C. H. BANTEL BRYANT SMITH The University publishes bulletins four times a month, so numbered that the first two digits of the number show the year of issue and the last two the position in the yearly series. (For example, No. 3101 is the first bulletin of the year 1931.) These bulletins comprise the official publica­tions of the University, publications on humanistic and scientific subjects, and bulletins issued from time to time by various divisions of the University. The following bureaus and divisions distribute bulletins issued by them; communications concerning bulletins in these fields should be addressed to The University of Texas, Austin, Texas, care of the bureau or division issuing the bulletin : Bureau of Business Research, Bureau of Economic Geology, Bureau of Engineering Research, Interscholastic League Bureau, and Division of Extension. Communications concerning all other publications of the University should be addressed to University Publications, The University of Texas, Austin. Additional copies of this publication may be procured from the Bureau of Business Research, The University of Texas Austin, Texas, at $1.00 per copy THE UNIVERSITY OF TEXAS PRESS ~ THE UNIVERSITY OF TEXAS BULLETIN No.3113: April 1, 1931 THE NATURAL REGIONS OF TEXAS By ELMER H. JOHNSON Industrial Geosrapher Bureau of Buaineaa Research Research Monograph No. 8 PUBi..eso BY THB UNIVERSITY POUR TIMBS A MONTH, AND BNTBRBD AS SEC9ND·CLASS MATTBR A.T THE POSTOPFICB AT AUSTIN. TEXAS, UNDER THBACT OF AUGUST 24. 1912 The benefits of education and of useful knowledge, generally diffused through a community, are essential to the preservation of a free govern· ment. Sam Houston Cultivated mind is the guardian genius of Democracy, and while guided and controlled by virtue, the noblest attribute of man. It is the only dictator that freemen acknowledge, and the only security which freemen desire. Mirabeau B. Lamar Copyright, 1931 by The University of Texas Bureau of Business Research CONTENTS Page INTRODUCTI0 N ---------------------------------------------------------------9 PART I. THE SETTING OF TEXAS IN THE SOUTHWEST --------------------------------------·-------19 PART II. THE TEXAS ENVIRONMENT ----------·· -· ----23 Climate and Weather --------------------------------------------·-----23 Physiographic Regions of Texas -------------------------------45 Natural Vegetation of Texas --------------------------------------59 Soil Resources of Texas ----------------------------------------------65 Oil, Natural Gas, and Other Mineral Resources_______ 78 PART III. NATURAL REGIONS OF TEXAS ______________ 85 East Texas Plains --------------------------------------------------------88 Interior Dissected Plains and Marginal Plains of Northeast Texas -------------------------__ _________________ _______ 91 The Rolling Plains ---------------------------------------------------94 Humid Coastal Prairies ----------------------------------_______ 96 The Prairies Province --------------------------------------------------99 The Black Prairies ----------------------------------------··--------!01 The Grand Prairies ___________________________________________________ l 06 The Coastal Prairies ________________________________________________ l 08 Interior Coastal Prairies __ ____ _____________ ____________________ l l 0 Eastern Cross Timbers _____________ _______________________________ 112 The Middle Texas Province ________________________________________112 The North-central Plains _______________________________________ l 16 Eastern High Plains _______________________________________________126 Edwards Piateau _____________________________________________________129 South Texas Plains ------------------------------------------_______133 Western High Plains and Trans-Pecos Country_______ l41 List of Maps and Charts Figure 1. Rainfall Map of Texas___________________________} In Figure 2. Temperature Map of Texas___________________ Pocket Figure 3. Average Length of Growing Season___ Figure 4. Temperature and Rainfall-Model __________________27 Figure 5. Temperature and Rainfall-Beaumont ____________28 Figure 6. Temperature and Rainfall-Nacogdoches ______29 Figure 7. Temperature and Rainfall-College Station____30 Figure 8. Temperature and Rainfall-Sugar Land__________33 Figure 9. Temperature and Rainfall-Fort Worth__________34 Figure 10. Temperature and Rainfall-Sherman ______________35 Figure 11. Temperature and Rainfall-Corpus ChristL___37 Figure 12. Temperature and Rainfall-San Antonio________38 Figure 13. Temperature and Rainfall-Amarillo ______________39 Figure 14. Temperature and Rainfall-Plainview ____________40 Figure 15. Temperature and Rainfall-Kerrville ______________41 Figure 16. Temperature and Rainfall-Fort Davis____________43 Figure 17. Temperature and Rainfall-Fort Mcintosh ____44 Figure 18. General Key Map of Texas Natural Regions -----------------------------------------------· In Figure 19. Detailed Key-Map of Texas Natural Pocket Regions -----------------------------------------------· Figure 20. Natural Regions Map of Texas_____________._ PREFACE The wide range in the natural resources of Texas in con­junction with the great size of the State presents a diversity of problems in the development of a comprehensive program for the most effective utilization of these resources. It is essential to recognize, also, that the production and accumu­lation of wealth in the State in the future as it has been in the past, will be dependent upon the economic use of the State's magnificent natural resources. Although the signficance of the economic utilization of these resources is obvious, it appears that this is a movement that has only well begun. The particular purpose of this publication is to delineate Texas regions as units which are necessary not only in making an analysis of the commercial aspects of the natural resources of the State, but also in establishing bases for the analysis of the economic development of the various sections of Texas as well as of the State as a whole. The method employed in this publication may be de­scribed as geographic correlation, that is, the interpretation of the areal extent and characteristics of regions in terms of relationships between the elements of the regional en­vironment insofar as these elements have an areal expression. This bulletin is the first of a series by Mr. Johnson deal­ing with resources of Texas and their utilization. It is essen­tially a comprehensive outline of this field of work, and will be followed by surveys dealing with the commercial development of Texas regions and of their natural resources as well as by more intensive studies of each region. The advantages of the method and the point of view utilized in this particular study arise from the fact that a large number of essential factors and their relationships through­out large extents of territory can be interpreted in brief space; furthermore, the significance of the natural re­sources and of the natural conditions under which the resources occur can be presented in clear perspective, and a basis thus provided for a better interpretation of the present economic development of the State as well as for charting the major points of the State's development in the future. The point of view and the type of materials presented in this study and the studies which are to follow are regarded as indispensable in formulating a business policy for the economic utilization of the vast and varied re­sources of Texas and the Gulf Southwest. A. B. Cox, Director. April 1, 1931. ACKNOWLEDGMENTS It is impossible to acknowledge fully the many sources of information used in the preparation of this bulletin or to give full credit to the many research workers whose materials have been of great value in furthering the field work upon which much of this publication is based. No bib­liography is included in this study, but it is hoped that an annotated bibliography can be prepared at a later time which will outline the source materials of Texas geography, both physical and economic. While the responsibility for the opinions and conclusions expressed in this bulletin rests upon the author, yet a great deal of whatever may be valuable in this publication has come through the writings and teachings of a number of research workers. Of these, the author feels under obliga­tion to Dr. C. K. Leith, Chairman of the Department of Geology, University of Wisconsin; Dr. H. C. Cowles, Chair­man of the Department of Botany, the University of Chi­cago; and to Dr. C. F. Marbut, Chief of Soil Survey, United States Department of Agriculture. Special acknowledg­ment is gratefully given to the great value of the wide range of writings and to the inspiration of the friendship of the veteran Texas geologist and geographer, Robert T. Hill. ELMER H. JOHNSON. Note. It should be emphasized that this bulletin presents only a comprehensive outline of the major physical aspects of the natural regions of Texas. This publication is designed to provide a basis for the forthcoming studies on the commercial development of Texas regions as well as for detailed studies of Texas resources and indus­tries with.particular reference to their relations to the natural regions of the State. This series of studies dealing with the interpretation of the characteristics and distribution as well as the inter­relationships of natural regions, of natural resources and their com­mercial accessibility, of business enterprises, and of population growth and concentration constitutes definite and concrete materials for the development of the concept of regional economics. The concept of regional economics includes interpretations of metropolitan regions, of agricultural sections, of industrial areas, and of trade and financial centers from the point of view of the regional environment concerned in the manifestations of these various types of economic adjustments·. INTRODUCTION LARGE PRODUCTION In today's commercial world, the production of goods in large quantities takes its place as one of the truly signifi­cant achievements of the past 100 years. Whether this production is mass production or only large in aggregate, it is always regionalized-certain regions stand out as pre­eminent in the production of a particular commodity or group of commodities. Furthermore, production is almost always localized-that is, certain areas within the larger region specialize in the production of certain goods. Local­ization of production is dependent on the possession of a combination of advantages which exist in the locality or area because of its setting in the regional environment of which the locality is a part. The relative importance of these advantages changes from time to time with devel­opments in technology and with the necessarily continuous adjustments of the region's economic life to national and world trade. The rise of large production and its consequent localiza­tion due to the influence of the comparative advantages of areas and regions is, however, dependent upon and de­termined by the tremendous increase in total consumption of the goods involved. The magnitude of industrialization which has taken place in the past half century, and much of it during the past twenty-five years, has been the deter­mining factor in the expansion of capacity for consumption for the products of national and world commerce. No one well acquainted with modern industrialization feels that this movement has reached anything like its limits in the expansion of markets for the commodities of commerce. It may be stated that the world has just begun to use its natural resources; and it has been upon the use of natural resources that this vast expansion in industrialism and the consequent concentration and extension of markets is de­pendent. EXTENSIVE NATURAL RESOURCES In any complete interpretation of the economic life of any section of the earth, it is necessary to obtain a broad perspective of the natural resources and their physical set­ting in that section. In today's business the possession of relatively extensive natural resources which are readily available under present conditions are the basic features which count in actual production, present and potential. Prior to the past 100 years the possession of fairly pro­ductive soils, to which was adjusted a relatively dense population, was the main factor which gave to a region its prosperity. During the past fifty years highly produc­tive soils of uniform nature extending over large areas of land surface have attained world-wide importance as cen­ters of agricultural production. This fact is obvious from even a cursory examination of graphic maps showing the course and extent of world trade in agricultural commodi­ties. But, in addition, certain minerals have recently at­tained tremendous importance in world affairs and world commerce. The wide importance of minerals in today's economy is attested by the fact that the world has used more of its mineral resources in the past twenty years than in all preceding history. Of the minerals, energy resource materials may be regarded as especially signifi­cant. In fact, the western world is dependent upon me­chanical energy to almost as great an extent as upon the supply of food. Of energy resources, oil, for example, has but very recently staged its rapid growth-a growth so rapid that the world has extracted more oil in the past nine years than in all preceding time. Industrialization based upon the widespread use of min­eral resources has accentuated and extended the comm-ercial phases of world agriculture. Industrialization has given the instruments necessary for technological revolutions that have occurred in agricultural production and. thus has pro­vided its extension to all the productive lands of the world; it has given the means· of transport which bring distant The Natural Regions of Texas lands in constant touch with rapidly expanding world mar­kets; it has made possible the effective utilization of vast resources of large soil areas, of extensive grasslands, and of luxuriant forests as well as of magnificent mineral deposits and accumulations which until recently in the world's history were unavailable to mankind. EFFECTIVE UTILIZATION There can be no doubt but that the effective utilization of a wide range of natural resources made possible by the rise of industrialism constitutes one of the major accom­plishments of recent time. Effective utilization may be a more intensive form of utilization; it may be, however, a very extensive form of utilization. The point to be con­sidered is that of the effectiveness of the adjustments in­volved-adjustments of the form and type of utilization to the conditions of the natural resources as they occur in their regional environment with the resulting expression of a marked specialization in production. The kind and degree of utilization will always reflect the forces of the market demand; but the consumption curve is rising-it is, in fact, rising faster than population is increasing. The scale on which consumption is rising and the extent to which production is rising with this curve can hardly be overemphasized if a long time point of view is taken of the situation. The history of agricultural expansion during the past fifty years and especially in the past twenty-five years shows the significance of large areas or regions whose agri­cultural resources enable such areas to produce in large quantities the staple agricultural commodities of the world's · commerce. It is not to be assumed that limits of agricul­tural production have been reached, either as regards quantity of production or of lower costs per unit of product. It is to be expected, however, that certain areas and certain regions because of the comparative availability of their resources will possess advantages over other regions both as regards potentialities of readily increasing production The University of Texas Bulletin or as to decreasing costs of production. For instance, everyone recognizes the different problems involved in fur­ther mechanization of agriculture-difficulties concerned · with the type of crop involved on the one hand or those con­cerned with the nature of the area or region on the other. That changes of great importance have been recently ac­complished in machine production in agriculture no one can deny. That considerable possibilities exist for the further extension of effective machine production in agriculture is generally admitted. A glance at a series of maps depicting world production and trade· in our agricultural commodities reveals in a striking way how far specialization and adaptation of the various crop plants and domestic animals to the different areas and regions of the earth's surfaces have already gone. Transportation improvements and the expansion of large markets have allowed the efficient utilization of those read­ily available agricultural lands of the world which wer.e free to develop a commercial agriculture. Detaned studies . of commercial agriculture reveal the dominating aspects of large areas of lands especially suited by nature for the · production of certain agricultural staples of world trade­a condition which prevails whether the lands be intensively devoted to the dairying industry, or to wheat or cotton or corn, or to such extensive agricultural operations as the grazing of sheep on the dry lands of interior Australia or on the less productive grasslands of interior Argentina. In regard to mineral consumption and production, the curve has been rising sharply since 1900; in regard to petroleum, the curve of consumption has been rising sharply since 1920; and the curve of large natural gas consumption apparently has just begun to rise. The large consumption of mineral resources since the turn of the century has been one of the most striking facts of all history. The reactions of the forces of this extensive movement have given a new . importance to regions which contain large reserves of these resources for which the world demand is already large, and which also is being rapidly extended. The significance of . The Natural Regions of Texas large reserves of energy resources and especially of oil and gas has already given the regions in which these accumula­tions occur a dominant position in the world's commerce and industry. In the formulation of future policies, whether political or economic, the predominance of large reserves of mineral resources readily available will have the center of attention; the practice of using bits of mineral resources to supply local markets has given way to the forces of a wider market whose curve of consumption as has been noted is a very rapidly rising one. SIGNIFICANCE OF THE REGIONAL CONCEPT Large production on a world scale, a result of the eff ec­tive utilization of extensive and readily available natural resources, has been accomplished by the specialization of production in those localities and areas which have par­ticular advantages for the supplying of the desired com­modities to the expanding world markets. In the case of staple agricultural commodities, and in the case of minerals needed in large quantities, regions with large reserves read­ily available of the desired commodities, are the ones that stand out as important in a world perspective of the past half century. It is impossible to increase perceptibly in human time the world's supply of natural resources; nature has given these resources once for all, in so far as the human race is concerned. Some resources such as natural gas are entirely consumed in their use; others, as soils, may be used over and over again provided proper care is taken ; still others, as forests or grazing lands, replace themselves with proper care. Since natural resources cannot be perceptibly in­creased and since their relative and absolute importance in the modern world is steadily increasing, it follows that regions possessing relatively large reserves of those natural resources of most importance in modern agriculture, com­merce, and industry, must necessarily be the regions which will command the greatest attention and may demand the keenest study in peace or in war in the immediate future. It may follow that with increasing expansion of produc­tion there will occur an even greater degree of regional specialization and concentration. Most certainly, many regions will increase their agricultural production enor­mously; others will intensify their industrial activities. No doubt the spread of industrial development will serve with other developments to increase the total world buying power and thus will further stimulate production. There can be little doubt, it appears, but that economic adjust­ments to regional environments with the accentuated utili­zation of the particular region's natural resources will re­flect the regional concentration of production and of popu­lation density and distribution. In other words, economic development of the future will reflect even more than now the individuality and the importance of regions in economic activities, whether these activities include ordinary buying and selling, retailing or wholesaling, or phases of world trade. It should be obvious that the buying power or the selling capacity of the region or its sub-divisions must be of great concern to the student of marketing or of inter­national trade, and to the investor as well as to the mer­chant or the banker. To pass in brief review, as has been done in the pre­ceding paragraphs, the primary relationships of large pro­duction, of extensive natural resources, of effective utiliza­tion of these resources in order to attain large production, and the consequent regional adaptations and local special­izations, is to show in perspective what are perhaps the most potent features of today's commercial world. The spectacular rise of large production based upon widespread utilization of natu:ral resources during the past fifty years may well be considered as possible indicators of even fur­ther expansion and of greater concentration in the imme­diate future. If such may be the case, and there are no real reasons to think otherwise, then natural resources and the natural conditions of the environment of these resources will take on even an added significance. Regional geography The Natural Regions of Texas in its physical aspects and in its economic relations will of necessity be given far more consideration in the imme­diate future than in the past. ECONOMIC GEOGRAPHY OF TEXAS The foregoing outline of high points of a world perspec­tive concerning natural resources and their commercial development provides a setting and a background in which any comprehensive interpretation of the economic geogra­phy of Texas, or, for that matter, any other section of the world, may be viewed. In other words, complete studies of the economic geography of the State will include interpre­tations of the resources and their commercial development from a world point of view; in the same way, the resources and the commercial development of the various sections of the State must be viewed in their relationships to the rest of the world. The steadily increasing significance of Texas resources and their efficient utilization in world affairs will be of much greater concern in the immediate future, and thus it is more than ever necessary to view these resources and the conditions of their efficient utilization in broader perspective. The potentialities of commercial development based upon the extensive surface natural resources and the vast quantities of sub.;.surface accumulations of mineral resources included within the boundaries of Texas pro­vide the essential bases for future economic and commercial development. Moreover, the location of these resources and their ready availability in conjunction with the physical setting of Texas in the Southwest gives to the State added possibilities-possibilities that already have been reflected and will be of even greater significance in the future in giving Texas not only a commanding position agricultur­ally, commercially and industrially in the Gulf Southwest~ but also a key position in the economic and business affairs of the nation. PHYSICAL GEOGRAPHY OF TEXAS Is it not logical to conclude from the foregoing discussion that the physical aspects of the State may be of greater importance than is generally believed; can it be possible, also, that these physical conditions and natural resources will have a future significance much greater than has ever been recognized'! It is certain that more complete analyses of the physical background of Texas business and commer­cial growth will be called for, not only by research agencies. but also by business men, as it becomes clearer that city growth, transportation developments, market expansion, and other phases of commercial development are dependent more and more upon proper utilization of the State's nat­ural resources. The method used in this study is that of analysis of the physical geography of the natural regions of the State. The sub-divisions of the State have been decreed by nature; they have come about by slow changes involving extensive lengths of time. Their natural development and their pres­ent features are marked by the inter-relations of every factor that constitutes a part of their environment. These inter-relations or natural adjustments between climate and natural vegetation, geological materials, and soils, and mineral resources find their best expression in the part they occupy in regions. They give the region its environ­ment. Analysis shows that this environment is made up of inter-locking and inter-related elements which have the common quality of areal distribution. The significance of any one of these groups of environmental factors, whether in a physical way or in an economic sense, is dependent upon the inter-relations of that group to some or all of the other groups of the environment. Hence, it is necessary to study resources, for example, from the point of view of their setting in the region; it is necessary, also, to study the utilization of these resources from the standpoint of their environmental or regional setting. Moreover, problems of the most efficient use of resources, the distribution and characteristics of types of farming, The Natural Regions of Texas localization of highly specialized farming operations, the distribution and location of manufacturing areas, all have their regional bases and reflect specific aspects of the areas or sub-divisions within the regions. The practical working out of problems of conservation is in reality a regional prob­lem; that is, the problem or problems must be seen in the light of the regional environment of which they are a part. This principle is as true of soil conservation, proper ter­racing or water control and moisture retention, as it is of proper care of range grasses or of forest resources. It is apparent to research workers that the physical geography of regions and of their sub-divisions is basic to a complete understanding of the problems and trends of commercial development; it is just as apparent that a scientific knowledge of regional environments will be of greater importance in the immediate future. The compara­tive advantages a region possesses will determine the posi­tion attainable by that region in the future. The employ­ment of the principle of geographic correlation is the only sure method thus far developed that will provide a compre­hensive view of the major aspects of those environmental factors that are specifically related to the most effective utilization of natural resources. Upon the groundwork of the physical geography of regions-in fact, growing out of it-mankind has erected the superstructure of a cultural landscape. The uses man makes of the natural region in his commercial development constitutes the theme of eco­nomic geography; these uses, because of their regional setting, have likewise a regional distribution and individual regional characteristics. No one can doubt the importance of the regional expressions of commercial development, that is, of the regional environment, whether that develop­ment be the concentration of cotton production in some Texas region, dispersion of steel production from the Pitts­burgh area, shifts in population distribution in the South, or the expansion of markets for products of Texas and the Southwest. Moreover, with the increasing complexity ot business organization and the widening of problems of busi­ness administration, whether in Texas or elsewhere, the importance of the regional features, physical and ecomonic, will command even greater attention. It appears obvious that it is more and more necessary to look ahead in agri­culture, in industry and in other forms of business; it may be that five-year programs are too short in order that the more desirable purposes be accomplished ; it may be neces­sary to look ahead for a period of ten or even twenty years if comprehensive programs of Texas business potentiali­ties are to be placed in proper perspective. If so, a start­ing point will always be the reserves and the distribution of the natural resources of the State. A second step may always be the setting of these vast accumulations and areas in the regional environment of which they constitute an integral part. An analysis of any economic or commercial development or any program which concerns future ad­justments which omits the regional aspects of the problems is to that extent incomplete. Any conclusion regarding potentialities in Texas business or possibilities in any line of business which neglects the regional aspects of natural resources, or the regional setting of commercial develop­ments, is to that extent immature and cannot be regarded as final or conclusi ve. PART I THE SETTING OF TEXAS IN THE SOUTHWEST ORIENTING FACTORS The general location of Texas in the Gulf Southwest and the specific location of the various sections of the wide and varied territory included in Texas constitute important considerations to be recognized in attaining a proper under­standing of the economic development of the State in the past and in interpreting present conditions of development in the different portions of the State. It is, perhaps, of even greater significance in securing a proper appreciation of the many complex economic problems which the people of the State will be required to meet in the future. Factual considerations that are significant in regard to the physical aspects of location of this territory are both general and specific. It is necessary to recognize both of these phases in order to appreciate the part played by natural and human factors in the attainment of the posi­ tion which Texas occupies in the economic life of the nation. Texas constitutes one-twelfth of the total area of the United States; it makes up a large share, in both areal and economic importance, of that section which is termed the Gulf Southwest. The Gulf Southwest embraces a large and important part of what is called the Inner Lowland of the United States-those vast plains interrupted here and there by mountainous elements (like the Ouachitas and the Ozarks), which lie between the Appalachian Mountain system to the east, and the front ranges of the Rocky Mountains to the west. The Gulf Southwest occupies the territory between the Mississippi river to the east and the Rocky Mountains to the west; it reaches northward to the State of Nebraska, and on the south is bounded by the Rio Grande and the Gulf of Mexico. The position occupied by Texas in the Gulf Southwest is commercially and economically a strategic one. Texas not only makes up an extensive share of this larger division of the country but it possesses also a strategic portion of the coast line of the Gulf of Mexico. Considering its natural resources in conjunction with its geographical setting there is no doubt that with increasing commercial development the location of Texas will assume an even greater impor­ance. Significant as are the factors of commercial accessibility by land and by water, the climatic factors associated with the location of Texas are of even greater importance. The territory of the State lies within the southern mid-latitudes, which in association with the generally low elevation of its surface gives a long and warm growing season. Its location with reference to the waters of the Gulf of Mexico and the wind systems which connect the western portion of the Gulf with the interior lowlands of the United States is of more than local importance in determining the total amount as well as the distribution through the year of precipitation in the various sections of the State. The Gulf of Mexico is the reservoir which supplies the moisture that makes possible the important and diverse crop and livestock pro­duction not only of Texas, but also of a very large propor­tion of the territory of the Great Plains and Prairies of the United States-a fact whose economic significance it would be difficult to over-estimate. Another significant aspect of the location of the territory of Texas is that of its relationships to the geological struc-· ture and the geological history of the United States. These relationships are important not only as an aid to an under­standing of the reserves and availability of the mineral resources of Texas but also to an appreciation of the char­acteristics of the surface f ea tures of the various sections of the State. An understanding of the geologic evolution and physiographic development of the various sections of the State is important also in interpreting the extension and The Natural Regions of Texas relationships of surface and sub-surface features in Texas to adjacent sections in adjoining states. VARIETY OF FACTORS WITHIN TEXAS Because of its location and areal extent, Texas presents a great variety of natural features; the State is, in fact, a meeting-place of a large number of elements of physical environment which extend into it in modified form from adjoining states. Eastern Texas is humid, and its climate is a western ex­tension of the humid climate of Louisiana. The climate of north-central Texas resembles that of adjoining sections in Oklahoma, while the climate of the western High Plains is very similar to that of adjacent portions of the High Plains of New Mexico. Eastern and south-central portions of the State belong to the Coastal Plain physiographic region; the Coastal Plain adjoins the Edwards Plateau along the Balcones Escarp­ment which forms the southern extremity of the Great Plains Province. That portion of the Coastal Plain which lies in eastern Texas is humid, but southwest of the Brazos, the climate grades through moderately humid to sub-humid conditions ; in the dissected margin bordering the Rio Grande, even drier conditions are found. With these changes in climate, the native vegetation changes markedly from . forests, through prairie and woodland, to short grass and chaparral. The High Plains and Edwards Plateau regions belong to the Great Plains Province; and the annual rain­fall of the High Plains varies from an average of about twenty-one inches at the east to fifteen inches along the western boundary of the State. Most of the Edwards Pla­teau possesses a sub-humid climate; but, because of physio.. graphic and other conditions, the influence of moisture on natural vegetation there differs considerably from that in the southern Coastal Plain, which also possesses a sub­humid climate. North of the Edwards Plateau and between the High Plains at the west and the Coastal Plains at the east lies the section which R. T. Hill called the Central Denuded Region which in this study is designated the North-central Plains of Texas. This section is the southern portion of the Central Lowland Province which includes a large share of the Mississippi basin. Most of trans-Pecos Texas belongs to the Basin-and­range physiographic province. This section of Texas is a part of the Western Mountain System of the United States and possesses sharp contrasts to the rest of the State which is dominated by the characteristics of a plains land­scape. The features herein sketched indicate a considerable variety and marked contrasts in the climatic conditions and physiographic characteristics of the various portions of the State. The physiographic characteristics and climatic con­ditions are fundamental in the making of the complex phy­sical environment of the State. The natural vegetation and the soil resources of the various sections of the State are derived features; both are dependent upon and have grown out of the environmental bases provided by climate, physiography, and geologic materials. Texas presents a wide array of soil areas and natural vegetation formations whose economic importance is obvious. A point to be em­phasized here is that the soil resources and the natural vegetation are closely related to the regional environment in which they occur. It is true also that the oil, gas, and other mineral resources of the State are very closely associ­ated with the areal and regional aspects of the great sub­surface regions in which they have become concentrated. PART II THE TEXAS ENVIRONMENT CLIMATE AND WEATHER Climate constitutes the most fundamental and the most far-reaching of all the elements which make up the natural environment of life. This is true whether the significance of climatic regions of the earth's surface are considered in general or whether an anlysis is made of the essential factors to life in any one of these regions. Weather types and weather changes within any of these regions may exert also very important influences upon the affairs of life, whether these conditions are those which affect air trans­portation, agricultural production, transportation of com­modities, or the yields and qualities of crops. Climate not only exerts a predominating influence upon the characteristics and the geographical distribution of nat­ural vegetation, but it also exerts just as strong an influ­ence, directly and indirectly, upon the characteristics and distribution of soil resources. Hence it is necessary to know definitely the climate of any region or area in arriving at the agricultural possibilities of its lands. It may be noted here, however, that the actual effects of climatic factors, especially rainfall, are themselves limited and often greatly modified by the characteristics and conditions of other ele­ments in the natural landscape, especially the factors of soils and of vegetation. In other words, climatic data, such as those of the amount of rainfall and its distribution, can­not be considered as ends in themselves even-in evaluating the moisture conditions of any area; the effects of moisture conditions must be related to other factors in the natural environment such as topography, character of the soil, the natural vegetation, and to the geological conditions imme­diately underlying the surface. In Texas, moisture conditions, especially their seasonal characteristics, are basic to an understanding of the utili­zation and the possibilities of the various regions in the State; moisture relations, likewise, are basic factors upon which sub-divisions of the territory of the State are made. It is well known that moisture conditions are fundamental factors in determining the yields of various crops and for­age plants; it is not so well recognized that moisture rela­tions have much to do with the quality of the product, whether the product be cotton, wheat, range grasses, or fruits and vegetables. In regard to Texas, the significance of mild winter temperatures over a large part of the State should be emphasized in relation to the growth of range grasses and winter pastures, and in the southern section, the producton of winter vegetables and of citrus fruits. The importance of the mild winter temperatures in conjunction with winter rainfall is of very great significance to the live­stock industry in Texas. Likewise, the mild winters to­gether with the sunshiny weather which prevail in a con­siderable area of the State, is becoming more important with the increase of winter tourists in Texas. In the same way, the open winters are of importance in the increase of highway traffic across the State, and especially in the growth of the southern trans-continental routes of travel. BASIC CONSIDERATIONS The dominance of a generally unbroken plains topo­graphy in the landscape of the State allows rather free sweep of both temperature and rainfall features across wide areas throughout the State outside the Basin-and-range areas of the trans-Pecos country.. Because of the effects of the sweep of climatic conditions in the plains area throughout the State, definite breaks do not occur between climatic regions or areas; but associated with these same factors sudden changes in weather in plains areas are likely to occur, especially during the winter part of the year. These sudden changes commonly termed "northers" are marked by falling temperatures and may be associated The Natural Regions of Texas with stormy weather, heavy rains, unseasonal cold spells, and sometimes unseasonal frosts. In brief, the zones of average rainfall have a north­south trend across the State (Fig. 1) with a gradual de­crease of precipitation from an annual average of fifty inches in the coastal section of eastern Texas to fifteen inches in the Pecos Lowland of the southwestern High Plains. In a general way, the zones of average temperature have an east-west trend across the State (Fig. 2). The highest average temperatures occur in the extreme southern portions of the State; there is a gradual decrease no:rth­ward, and in northwest Texas the higher altitudes of the , Panhandle High Plains reduce the average annual temper­atures to around 56°. Figures 1 and 2 are in the pocket at the end of the bulle­tin. Annual averages of either rainfall or temperature may have little direct significance except in presenting a broad picture of the distribution of these climatic factors in the State. Indirectly, the annual averages by months are of great value in view of the fact that the seasonal aspects of both rainfall and temperature factors bear a direct relation to the average conditions of rainfall and tempera­ture respectively. Furthermore, the fact that the results of the criss-crossing of the north-south rainfall belts and the east-west temperature belts give to the State a checker­board arrangement in regard to rainfall-temperature com­binations is of great significance in blocking out and in­terpreting the major climatic divisions of the State. LENGTH AND TEMPERATURE OF THE GROWING SEASON Along with the distribution of temperature and moisture factors must be considered the length and the distribution of temperatures during the growing season. Figure 8 shows the · length of the average frost-free season for the entire State. Figure 3 is in the pocket at the end of the bulletin. The longest growing season in the State is in a narrow zone of country adjacent the coast and extending from Houston to the mouth of the Rio Grande. The length of the frost-free season gradually diminishes northward and northwestward, with sudden decreases where the elevation rises perceptibly, as along the Balcones Escarpment and the "cap-rock" escarpment at the eastern margin of the High Plains. The combination of temperature-rainfall conditions in the various portions of the State is obviously of funda­mental importance directly to be crop production and range conditions; moreover, the indirect influences of rainfall­temperature combinations and resultant effects on evapora­tion in determining the types and kinds of natural vegeta­tion and in affecting the kinds and productivity of the soil resources of the region are also of vast significance. SIGNIFICANT TEMPERATURE-RAINFALL CHARACTERISTICS IN TEXAS Eastern Texas The East-Texas Timbered Plains and the Coastal Prairies strip from Galveston Bay eastward have a humid climate, the eastern portions being more humid than the western. The total rainfall of this region varies from an annual average of forty inches along the western margin to fifty inches along the lower section of the Sabine. Because of the heavy total rainfall in this portion of the State and its fairly uniform distribution through the year, there is usually an abundance of moisture. This condition is particularly true of the eastern portion; the western and interior areas, however, not only have less total rainfall but the distribution through the year is also less regular. As a result, droughts sometimes occur in the western mar­gins of this division, and the effects of the rainfall regime is reflected in the different aspects of the natural vegetation of the eastern and western sections of this division. 0 120 0 100 0 TEMPERATURE AND RAINFALL D RANGE FROM JIAXD(U)I TDIPERATUJtE TO KAXIKUJI JIEAN ~ JIEAN TEJIPERATURE ~ 8.ANGE FROJI JIINlllUJI MEAN TO KlNlllID( TEJIPEJlATlJRE II RAINFALL ABSOLUTE MAXIMUM ~ (DEGREES F.) 4! MEAN MAXIMUM MEAN MEAN MINIMUM A8$0LYTE MINIMUM RAINFALL INC .S MODEL CHART ,, 14 ,, 12 " 10 II 8 II 6 4" ,, 2 0" •ao'---------------------------------------------------------­ FIGURE 4. Temperature and Rainfall Chart-Model. Monthly data of rainfall and temperatures for typical points in the State are represented in a series of charts. In each case the data are combined in one chart for each point. The average rainfall for each month is in each case expressed in inches. The temperature data are expressed in degrees Fahrenheit. These temperature data include: Absolute Maximum, whch is the highest temperature in each month during the period of years used; Mean Maximum is the aver­age maximum; Mean Minimum is the average minimum; Mean Tem­perature is the average of the mean minimum and mean maximum; Absolute Minimum is the lowest temperature recorded in the different months during the period involved. Data in all cases are taken from published materials of United States Weather Bureau. Referring to Figures 5, 6, and 7, it is seen that the tem­perature regime of the three stations, Beaumont, Nacog­doches, and College Station, is in most respects very similar. 0 14'0 0 20 0 100 TEMPERATURE AND RAINFALL BEAUMONT D llANGE FROM KAXIllUll TEMPERATURE TO KAXIKUK MltAN "°" KEAN TEMPERATURE II RANGE FROM MINl)(UJI MEAN TO llINIKUV TEMPERATURE -RAJNFA. ,, 14 ,, 12 a' ,, 2 0" 0 ________________________________________________..J •20.._ FIGURE 5. Period of 20 years. Elevation 29 feet. The Natural Regions of Texas Similarities in the distribution of these average tempera­ture data are to be expected in view of the proximity of the location of these stations in the plains section of eastern Texas. 0 120 TEMPERATURE AND RAINFALL NACOGDOCHES D RANCE FROK KAXDIUll TEKPEBATUllE TO KAXDIUll KEAN .<)-. KEAN TDIPERATURE Eil RANGE FROM llINIJllUll KEAN TO JllI1'111UX TEllPUATUBE II RAINFALL ,, 14 12" ,, 10 a" 6" 4" II 2 II 0 -20.....__________________________________________________, FIGURE 6. Period of 21 years. Elevation 271 feet. Because, however, of the variation in the distances of ·these stations from the Gulf of Mexico and on account of their different locations with regard to effects of seasonal 0 140 0 120 108 -20----------------------------------------------------~ FIGURE 7. Period of 29 years. Elevation 308 feet. TEMPERATURE AND RAINFALL COLLEGE STATION D R.\NGE FROM MAXIMUM TEMPERATURE TO MAXIMUM MEAN ~ MEAN TEMPERATURE ~ RANGE FROM MINIMUM MEAN TO MINIMUM TEMPERATURt: II RAINFALL II 14 II 12 10" II 8 6" II 4 II 2 II 0 The Natural Regions of Texas wind systems, the rainfall regime, on the other hand, ex­pressed here only in monthly means for these stations, varies considerably in the areas concerned. Beaumont has the highest rainfall of the three, as might be expected because of its proximity to the Gulf of Mexico, and the distribution through the year is rather uniform. No month has an average of less than two inches. Two rather well marked maxima are obvious. The highest and longest of these maxima is that of the summer, correspond­ing with the maximum of temperatures. The winter maxi­mum occurs in only one month, December. Nacogdoches has a high average rainfall-more than forty-six inches per annum. As in the case of Beaumont, two maxima are marked, but the sun1mer maximum differs greatly from that of Beaumont; and the depth and width of the troughs between the maxima at Nacogdoches are greater than is the case at Beaumont. The summer maximum comes earlier in the season at Nacogdoches and is higher than at Beaumont. These con­trasts are associated with the effects of the continental or interior influences on the climate of Nacogdoches in con­trast with the marine (Gulf) influences on Beaumont. College Station records other significant contrasts. Al­though this station is located about the same distance from the Gulf as is Nacogdoches, the annual rainfall averages eight inches less. The lesser total rainfall and the relatively lower summer rainfall are associated with the more west­erly location of College Station in the State and thus to the accentuated influences of continental factors on climate and weather. Some of the physical influences of these varying climatic conditions in the humid lands of eastern Texas will be pointed out in following sections of this study, for instance, those dealing with natural vegetation, soils and the natural . regions. The Prairies West of the humid timbered country is a zone of lands occupied by the Texas Prairies. Climatically this zone is a transitional division. The amount of rainfall decreases perceptibly westward and southward across the State. The average rainfall for this division of the State is not only less but its occurrence through the year is more irregular than that of the eastern portion of the State. The eastern portions of the Prairie division or province are humid but less so than the country along the Sabine river. The western margins of the Prairie division merge into the sub-humid lands. Taken as a whole the Prairies province of Texas has a late summer dry season. Because this province is distinctly a transitional zone, physiographic features and geological materials are very significant in reflecting different expressions of climatic influences upon the characteristics of the natural vegetation and the soil resources and consequently upon the agricul­ture in the zone. The Texas Prairies division is moderately humid. ·The average annual rainfall varies from thirty inches along the western margin to forty inches along the eastern bound­ ary. It is generally moist throughout the year, but dry spells are more common than in the humid lands east of this division, and droughts sometimes occur in the interior and northern portions. As the name indicates, the division is dominated by prairie country. The grass lands occupy the fine-textured soil areas such as the Black Prairies region. Extending between the prairie regions are sandy strips which are wooded. The best known of these wooded strips is the Eastern Cross Timbers. Because this division climatically is a transitional one, the rainfall regime of typical areas possesses some of the features common to the humid lands, but in the north prairie section the rainfall characteristics reflect some of the attributes of a sub-humid regime. The Natural Regions of Texas The average annual rainfall at Sugar Land (Fig. 8) is nearly forty-three inches or about ten inches greater than that of Fort Worth, but the average temperature at Sugar Land is considerably greater than that at Fort Worth. It 0 140 0 120 TEMPERATURE AND RAINFALL SUGARLAND D JLUfGB FROll KAXIllUJI TEllPBRATURB TO JIAXDIUJI JIUN -0-KEAN TEllPER.U'UBE II :&ANGE FBOll XINDllJll llEA.N TO XINIJIUJ( TDIPE&ATtmg 11 BAiNFALf· II 4 II 12 II 8 ,, 6 II 2 II 0 J F M A M J J A S 0 N -20._____________________________________________....... ~ FIGURE 8. Period of 19 Years. Elevation 79 feet. will be seen also that the average annual rainfall at Sugar Land is about five inches less than it is at Beaumont, which occupies an analogous location insofar as distance from the Gulf is concerned in the humid coastal prairies. Sugar -20._________________________________________________________, FIGURE 9. Period of 22 years. Elevation 670 feet. 0 1140 0 .aoo TEMPERATURE AND RAINFALL FORT WORTH D ~GS FROlll KAXIKUX TEXPERATVRE TO JIAXIXUK KEAN ~ KEAN TEKPERATURE ~ RANGE FROM MINIMUM: MEAN TO XINDCUK TEKPERATURE -RAINFALL 14" ti 12 II 10 8" 6" II 2 ,, 0 The Natural Regions of Texas Land has a heavy summer maximum well distributed throughout the summer, whereas Fort Worth and Sherman possess rather sharp summer maxima which are typical of sub-humid climates. 20'---------------------------------------------------­ 0 40 20 0 0 00 TEMPERATURE AND RAINFALL SHERMAN D RANGE FRO)( kAXIMUX TEMPERATURE TO )(AXIXUll MEAN -0 XEA:llo TEMPERATURE II RANGE FROJI JIINIJIUM KEAN TO J(JNl)(OJ( TEMPERATURE -RAINFALL 14" 0 12 ,, 10 ,, & 6' II 2 ,, 0 Fort Worth (Fig. 9) not only has less rainfall than Sherman (Fig. 10), but the regime is somewhat different. Both possess an early summer maximum. But the rainfall at Sherman (and the same is true of Greenville, for in.. stance) during June and the succeeding summer months is perceptibly higher than it is at Fort Worth. Middle Texas Provinces and Western Texas West of the Prairies province is a wide extent of sub­humid country comprising parts of several physiographic units which naturally group themselves into three divisions. At the north are the North-central Plains and the eastern High Plains. The southern division comprises the south.. western portion of the Coastal Plain in Texas, and the term South Texas Plains is here used for that division of the State. Lying between the South Texas Plains and the North-central Plains division is the Edwards Plateau. Corpus Christi (Fig. 11) illustrates the rainfall regime of the coastal country of this sub-humid province. Its average annual rainfall is about twenty-five inches as con.. trasted with an average of nearly forty-eight inches at Beaumont or of thirty-six inches at Victoria. All of these stations are in the Coastal Prairies physiographic region; the contrasts in the average rainfall at these stations reflect some of the reasons for subdividing this physiographic unit. The total average rainfall at Corpus Christi is a little less than that at San Antonio (Fig. 12) ; the general dis­ tribution of rainfall through the year is similar for both stations, although it is more uniform at San Antonio. In both cases there are two maxima which occur in spring and in autumn. The rainfall regime for Amarillo in the eastern High Plains is illustrated in Figure 13. The average annual rain­ fall is nearly twenty-one inches, but the average tempera.. tures are lower than at either San Antonio or Corpus Christi. Lower temperature in the northern portions of the High Plains decreases perceptibly the amount of evapora­ tion. The Natural Regions of Texas The distribution of rainfall at Amarillo is different from that at San Antonio. San Antonio is near enough to the coast and is so located with reference to winds from the Gulf as to have its rainfall distribution affected perceptibly 0 140 0 120 0 100 0 0 J TEMPERATURE AND RAINFALL CORPUS CHRISTI D lUHGB PllOJI llAXDlUJI TEKPE1lATU1lE TO KAXDUJK llEAM ~D.ur TDIPDATUU lil I.ANOS P801l llINDIUJl. llEAN 'l'O llINDltJJI TEllPEBATVU II JWNULL F M A M J J A 14" 12" ,, 10 II & 6" ,, 4 II 2 II 0 20'----------------------------------------------...... FIGURE 11. Period of 34 years. Elevation 20 feet. The University of Texas Bulletin by Gulf influences. The rainfall distribution of the north­ern High Plains of which that at Amarillo is an example, is dominated by continental influences. Its location gives to the section centering about Amarillo a regime typical of -20.___________________________________________________. TEMPERATURE AND RAINFALL SAN ANTONIO 0 140 D JtAM'•• l'BOK XAXIXUll TEMPERATURE TO XAXIMUX XEAN -0-JIJ:Alf TEMPERATURE m~Q·FllOJI JIJ:NIJCUK KEAN TO JllNlMUK TEKPEBATtraB 0 II RAINFALL l20 II 14 12" II 2 ,, 0 The Natural Regions of Texas interior grassland regions-a distinct summer maximum and a low rainfall during the winter season. The marked summer maximum is even better illustrated by the rainfall distribution at Plainview and in the eastern High Plains (Fig. 14). ' 14 12• The rainfall regime in the North-central Plains is similar to that at Amarillo as is illustrated in the distribution of rainfall at Albany. The average annual rainfall at Albany is four inches greater than at Amarillo; the temperatures, 0 140 0 120 0 100 TEMPERATURE AND RAINFALL PLAINVIEW 0 I.ANGE BOii JIAXl)(UJI TEMPERATURE TO llAXDIUll KEAN ~llJ:AN TEllPERATURJ!: ~M>lCE Jl'ROJI JIINIKUll KEAN TO JIINIKUX TEKPERATURJ!l • ltAINFALL 14" I~ -20...___________________________________________________. The Natural Regions of Texas however, are higher at Albany. The distribution of rain­fall at Albany is similar to that at Amarillo, the summer maximum being well marked. Because of locational features, the climatic characteris­tics of the Edwards Plateau country are transitional be­ •20._________________________________________________... 0 140 0 120 0 100 TEMPERATURE AND RAINFALL KERRVILLE D RANCE FROM MAXIMUM TEMPERATURE TO MA.XIMl.JX KEAN ..()-MEAN TEKPERATURE Ill RANCE FROM MINIMUM MEAN TO MINIMUK TEKPEJlA.TURE -RAINFALL 14" H 12 ,, 10 ,, 8 ,, 6 The Uni-versity of Texas Bulletin tween the South Texas Plains and the North-central Plains. The temperature-rainfall regime of Kerrville (Fig. 15) may be taken as typical of the Edwards Plateau. The average annual rainfall is a little more than at San Antonio, and the average temperatures are somewhat lower than at San Antonio. The maximum rainfall occurs during the late spring. The summer and autumn rainfall is fairly heavy, while winter is the season of lowest rainfall. In other words, the heaviest rainfall occurs in the growing season; there is no marked summer decrease as at Corpus Christi or San Antonio; on the other hand, Kerrville does not have the marked summer maximum of rainfall so characteristic of the High Plains (Painview) or the North Texas Plains (Albany). The cool-season rainfall in the Edwards Plateau is of great significance not.only for winter grazing but also as an important factor in the storage of moisture for use during the summer. Westward beyond the eastern High Plains and beyond the summit of the Edwards Plateau the amount of rainfall decreases gradually. The occurrence of the marked sum­mer maximum is of great importance to plant growth in these areas. The western High Plains has even a more marked summer maximum than has the eastern High Plains. The rainfall regime of Fort Davis is shown in Figure 16. The maximum occurs in late summer and early fall, a distribution which is very similar to that at Fort Stockton. In both cases the rainfall during the winter part of the year is low. Adjacent to the Rio Grande and extending from northern Maverick County to and including Starr County is a zone of eroded country which although it has about twenty · inches of annual rainfall, is subjected to high temperatures. The rainfall-temperature regime of Fort Mcintosh is shown in Figure 17. The distribution of rainfall is similar to that The Natural Regions of Texas at Corpus Christi; but the average rainfall, however, is perceptibly lower than at either Corpus Christi or San Antonio. TEMPERATURE AND RAINFALL FORT DAVIS D RANGE FROK MAXIMUM TEMPERATURE TO MAXIMUM KEAN '"(>-MEAN TEMPERATURE r:a RANGE FROM KINIKUM KEAN TO MINIMUll TEMPERATURE -RAINFALL ,, 14 It 12 It 10 The University of Texas Bulletin 0 140 0 120 TEMPERATURE AND RAINFALL FORT M~INTOSH D RANGE FROM XAXIKUJI TEMPERATURE TO KAXIXUX KEAN -er KEAN TEMPERATURE II RANGE FRO• KINJKUJ( MEAN TO MINIMUM TEMPERATURE RAINFALL - II 14 Ii 12 ,, 8 II 6 II 4 II 2 II 0 J F M A M J J A s 0 N D -20.._________________________________________________________, 0 FIGURE 17. Period of 53 years. Elevation 460 feet. The Natural Regions of Texas PHYSIOGRAPHIC REGIONS OF TEXAS Physiographically, the major area of the State is made up of a series of plains. Each plain possesses an individu­ality of its own because of its own set of local features. Local features which belong to the various plains units, however, may be very important in determining the poten­tialities of a particular area for certain crops. Each plains unit may be regarded as one of a series of extensive steps which extend from the low flat lands along the Gulf Coast across the interior part of the State to the higher elevated table-lands of the High Plains of northwestern Texas. The plains characteristics allow the wide sweep of the climatic factors across the State. Sudden changes in the climatic characteristics of any extent of territory are often associ­ated with marked contrasts in elevation. The dominance of plains features in the State, however, permits sudden weather changes, especially those associated with the pas­sage of "northers" across the State. Because of the characteristics of location and the dom­inance of plains topography, the climatic divisions of Texas are extensive in area. It is true also that the major physio­graphic regions are extensive; but the major physiographic regions present a variety of local features whose extent and characteristics are very significant. The larger physio­graphic regions and their local areas or sub-divisions con­stitute the subject material for this portion of the study. The succeeding sections on natural vegetation and on soil resources will illustrate not only the more important inter­relationships between the climatic regions and the major physiographic regions of the State, but also some of the more significant features of the local areas and sub-divi­sions of the major physiographic regions. Many of these physiographic features are indicated in the general key-map (Figure 18), which is in the pocket at the end of the bulletin. BASIC CONSIDERATIONS The plains regions of Texas are underlain by nearly horizontal or slightly dipping strata of sedimentary ma­terials. If the materials immediately underneath the sur­f ace are nearly horizontal, as in the case of the High Plains or of the Edwards Plateau, the topographic characteristics of the area or region are determined simply by the effects of erosional agencies upon these capping materials. If the strata are dipping, the outcrops of various types of strata generally present differential properties of "hardness" or "softness" to the forces of erosion and the resulting topog­raphy is composed of alternating lowlands and ridges or uplands. These topographic features of lowlands and intervening ridges or higher and usually rougher belts caused by dissection of strata outcrops of differential re­sistance introduce a complexity into the physiography of such areas which is in marked contrast to the more uniform conditions characteristic of areas capped by resistant hori­zontal strata. The physiographic history of the various plains regions of the State is very significant in determining the char­acteristics of the region as a whole and is especially im­portant in determining the surface characteristics of the areas which the major regions comprise. Also the geological development and characteristics of the strata underlying the various plains regions are of great importance in interpret­ing sub-surface conditions and thus in understanding the essential characteristics of the mineral resources of the State. It has been stated previously that the various plains regions in the State are portions of much larger provinces which extend into Texas from the outside. These physio­graphic provinces include the Great Plains, the Central Lowland (in Texas the Central Denuded Region), and the Gulf Coastal Plain. The Natural Regions of Texas THE GULF COASTAL PLAIN IN TEXAS The Gulf Coastal Plain is the largest physiographic di­ vision in the State. Its importance from an economi.c point of view is reflected in the fact that it includes the main forest areas of the State, the grazing lands of the Coastal Prairies, and the agricultural areas occupying the black soils of the Black Prairies, of the Coastal Prairies, and of the Interior Coastal Prairies. It includes also the oil fields of the Coastal Prairies country (the Salt Dome district) and those of the Fault-zone section (Powell, Wortham, Mexia, and those at Salt Flat, Luling, Darst Creek, and the newly developed Van field). The Gulf Coastal Plain has also the larger share of the population of the State, and in it are located such cities as Dallas, Fort Worth, Houston, San Antonio, Waco, Beau­ mont, and Corpus Christi. The materials which comprise the strata of the Coastal Plain in Texas are sands, clays, marls, and consolidated members such as sandstones, shales, and limestones. The strata of these materials in a general way dip faintly Gulfward. The older strata dip successively beneath the next younger ones, and the outcrops of the older materials are at the interior margins of the Coastal Plain. The trend of outcrops of these strata is roughly parallel to the Gulf coastline. This condition is particularly true of the coastal strata. In the interior, variations from this general rule occur such as those of the Interior Dissected Plains of northeast Texas which lie between the Sabine Uplift to the east and the Black Prairies to the west These beds at their outcrop differ not only as to area, trend of exposure and as to geologic materials, but also as to compaction and degree of consolidation. Hence, the materials ·of the outcrons resist erosion and dissection · un­ equally. The result is the variety of topographic features .illustrated in the Coastal Plain province in the State. Topographic Features of the Coastal Plain in Texas The streams of the Coastal Plain like those of other por­tions of the State flow Gulfward and thus indicate the general slope of the land surface. The surface of the country immediately back from the coast for a distance of from fifty to sixty miles appears extremely flat; it is almost level, and lies below an altitude of 100 feet. Practically the whole zone is a constructional surface, and its elevation is too low to allow much dissec­tion. Detailed observations reveal, however, the presence of minor variations in the flattish landscape, such as low hills, ridges, and elongated shallow lowlands. This zone is known as the Coastal Prairies because of the dominance of tall grasses in its natural vegetation. The zone is crossed by several streams; in the eastern portion, the wide alluvial strips are low and wet; in the middle section, crossed by the Colorado and the Brazos, the wide flood-plain materials merge into the adjacent prairies ; southward, the streams flow through somewhat deeper grooves in crossing the prairies zone. To the interior from the Coastal Prairies, the Coastal Plain has been subjected to considerable erosion and dis­section. The interior lands are older and the elevation is greater than in the coastal areas. Because of the action of erosional agencies upon outcrops of strata possessing differential degrees of resistance, the resulting dissection has produced a variegated topography of elongated lowlands with intervening ridges. The varia­tions in surface features are associated closely with the characteristics of the geologic materials of the outcropping strata. Nowhere in the Coastal Plain does any great amount of relief occur; however, the degree of relief increases in­teriorward, and certain sections of the Dissected Plains of northeastern Texas possess considerable relief. In general, the topography of the interior portions of the Coastal Plain bears a direct relation to the character­istics of the outcropping materials. Resistant strata such The Natural Regions of Texas as sandstone beds and hard limestone members stand out as ridges more or less modified by the action of stream dis­section. Usually such ridges possess a marked degree of angularity with considerable sharpness in surface features. Intervening beds of less resistant materials have been eroded sufficiently to form lowland strips of variable width; usually a considerable variety of local features has been formed on the floor and margins of these lowland belts. The result is the belted plains topography which character­izes the whole of the Coastal Plain province. Examples of such plains are the Grand Prairies, the Black Prairies, the Interior Coastal Prairies, and intervening ridge strips such as the Eastern Cross Timbers, the ridges produced by the Carrizo sandstone formation and such escarpments as those produced in places by the Austin Chalk in the northern Black Prairies. The ridges and escarpments are more or less rugged, depending upon the stage of their dissection. Subjected to continuous erosion, soils are usually thin and rock expo­sures are numerous. Hence the lands are not well adapted to farming. Where the surface materials are high in lime; these hilly lands are well adapted for pasture, as in the Black Prairies or in the "Red Lands" country of northeast Texas; in areas where these materials are mostly non-limy sands, and the climate is humid, the lands are usually ex­cellent for the growing of timber. On the other hand, the lowlands with their gently rolling topography, particularly those developed on limy materials, are the areas best suited to farming, provided the rainfall is heavy enough. Typical examples of such lowlands with their deep rich soils are the Black Prairies and the Interior Coastal Prairies. As has been shown in the section on climate, the climatic features of the Coastal Plain province in Texas range from humid in the lower Sabine section through the moderately humid and sub-humid lands into the drier climate of the southern portion of the State. Succeeding sections will show the reactions of the natural vegetation and of soil resources to these contrasted climatic conditions. The Texas Coast Line The Gulf coast line from the mouth of the Sabine to the lower Rio Grande is characterized by a variety of physical features. It is a segment of a great arc which extends. along the western shores of the Gulf of Mexico. Because of the geological nature of the coastal country, most of it is low in elevation. Because of the geological materials and the physiographic history of the coastal zone, the irregularities which occur in the contour of the coast­line are of three types: (a) the low, elongated, off-shore sandy islands, of which Padre and Galveston islands are examples; (b) the irregular V-shaped indentations or bays, such as those of Galveston and Corpus Christi; .and (c) delta formations or the accumulations of the sediments carried down and deposited at the mouths of such rivers as the Rio Grande and the Brazos. Behind the low, sandy islands lie long, shallow, elongated lagoons. Back of the lagoons, the coastal country is low. East of Matagorda Bay, it is especially low and much of it is marshy, whereas southwestward from Matagorda Bay the coastal country gradually increases in elevation to and beyond Corpus Christi Bay. The higher elevation and the less rainfall southward are factors which influence the development of the high grade cotton lands typical of which are those in Nueces County. The commercial significance of the physical conditions of the Gulf coastal zone in Texas is reflected when such features as the following are considered: (1) The development of ports and the growth of cities in the Sabine district, the Houston-Galveston area, and on Corpus Christi Bay; (2) The concentration of railways and pipe lines. in these areas; (3) The growth of diversified industries in these rapidly developing commercial districts. The Natural Regions of Texas THE GREAT PLAINS PROVINCE IN TEXAS The Great Plains province in Texas is a large section of country which is the southern extension of a large physio­graphic division which extends northward from the Rio Grande across the western plains of the United States into Canada. The southern extension of this province term­inates in Texas, and includes several well-marked sub­divisions. These sub-divisions comprise the Edwards Plateau and the Stockton Plateau, both of which lie entirely in Texas, and the High Plains and the Pecos Lowland, both of which extend from western Texas across into east­ern New Mexico. In general, the Great Plains province is characterized by the predominance of flattish to rolling plains country but it is not without many marked irregular­ities in its surface features. Because of these differences, the major sub-divisions of this province in Texas are here discussed individually. The High Plains The High Plains in themselves comprise a large physio­ . graphic unit. They are bounded on the east by the "cap­rock" escarpment and on the west and southwest by the Pecos Lowland. At the southeast they appear to merge into the Edwards Plateau country. The High Plains con­sist of broad, slightly rolling to undulating lands whose materials were deposited in smooth, coalescing alluvial-fan plains of vast extent. These sands, clays and silts were carried down from the highlands and mountains at the west by numerous streams which spread the sediments in broad fan-like forms in some cases hundreds of feet in thickness. Sheet erosion and deposition associated with wind activity have further modified the surface features and the disposition of these sediments. The High Plains country is entirely cut across by the wide and rather deep erosion groove of the Canadian river in the Panhandle section. Adjacent to this well-marked cut across the plains are strips of rough land produced by the erosional effects of many minor tributaries of the Canadian. Some of the headwater tributaries of the Brazos, the Red and the Colorado rivers have their source near the western margin of the High Plains and thus after heavy rains flow nearly across the entire width of this table-land. Along the eastern margin some of these streams have cut deep gorges, such as the Palo Duro Canyon in Armstrong and Randall Counties. Thus have physiographic agencies influenced the present topography of the High Plains-by sheet erosion and wind action on the surface materials, by erosional cuts across the plains table-land, and by the constant undermining and westward cutting by streams along the eastern escarpment. In addition, from the southwest, sand materials have been carried eastward by wind action, and deep sand areas cover large sections of the southwestern portions of the High Plains. The High Plains are economically a very significant unit. They possess a wide range of natural resources: soils, nat­ural vegetation, oil and gas, gypsum, and potash minerals. Agriculturally, the High Plains include the extensive wheat lands of the Panhandle, and the well-known cotton lands of the east central and southeastern High Plains. Through­out most of their extent, grain sorghums are grown suc­cessfully and ranching enterprises are of great importance. In recent years, the development of oil and gas resources has brought new economic interests to these West Texas lands. These enterprises are especially significant in the Panhandle and in sections of the southwestern High Plains. The Edwards Plateau The Edwards Plateau is the southern extremity of the Great Plains province; it is an extensive limestone table­land which does not possess the deep, loose, sandy and silty covering which characterizes the High Plains country. The Natural Regions of Texas The interior of the Edwards Plateau is an undulating to slightly rolling landscape whose flattish aspects are broken here and there by stream grooves. The marginal areas are eroded and more or less dissected. To the south and east, the plateau country grades down­ward to the rather sharply marked zone of the Balcones Escarpment; northward, another type of marginal country merges the Plateau with the lands cut through by the Colorado river. Beyond the Colorado lie areas which pos­sess many features in common with the Edwards Plateau country. These areas include isolated islands or outliers which are erosional remnants of a former larger extension of the Edwards Plateau, such as the limestone capped up­lands of the Callahan Divide which lie south of Abilene and Sweetwater. Likewise, the thoroughly dissected limestone country which R. T. Hill termed the Lampasas Cut Plain has many features that are similar to those of the Edwards Plateau. Westward, the Plateau upland grades down to the Pecos Lowland through a zone of rather deeply and generally thoroughly dissected country. West of the Plateau and beyond the Pecos river is the dissected limestone upland of the Stockton Plateau which is a modified continuation of the Edwards Plateau country. Centering about the Llano river in Llano County is an area differing considerably from the surrounding country; physiographically it is a unit of the Central Denuded Region of Texas. The basin of the Llano river is cut in granitic and more or less metamorphosed rocks of the Llano Uplift. Adjacent to and surrounding the granitic basin are basin­facing escarpments composed of sedimentary strata. The whole district comprising the roundly rolling granitic country and the eroded basin-facing escarpments will be referred to as the Llano area. In the Plateau proper, the interior, slightly rolling, and undulating lands possess fairly deep accumulations of soils and soil materials. The margins of the Plateau, on the other hand, due to their dissected nature are strongly erosional; hence soils on such areas are usually thin with bare rock surfaces covering considerable area, and deep accumulations of soil materials exist only in spots. It is obvious, then, that the Edwards Plateau is made up of a number of topographic areas and that each of these areas possesses individual climatic and other natural char­ acteristics. The results of these differential factors are expressed distinctly in the natural vegetation covering of the various physical sub-divisions of the Plateau. Obviously, it is necessary to have scientific analyses of the distribution of the various surface features of such a region if its eco­ nomic and commercial problems are to be properly inter­ preted and appreciated. North-Central Plains The term, Central Province, was long ago applied by R. T. Hill to the dissected and eroded country which lies between the Coastal Plain province on the east and the "cap-rock'' escarpment of the High Plains on the west and extends southward to the Edwards Plateau. This section, which is here designated the North-central Plains, is the southwestern extension of the Central Lowland physio­graphic province which is so important in central United States. Physiographically, as well as in other ways, this section . is complex. The major trends of its various units are north­south except in case of the Llano country which comprises a special physiographic and geologic feature. In this study the Llano area is classed with the Edwards Plateau. Except for the Llano area, the North-central Plains are made up of a series of plains and low plateaus, the surface of which bevels across the outcrops of gently inclined sedimentary strata. The strata of practically the entire province dip westward; in fact, the province occupies the eastern limb of an extensive geo-syncline which is commonly termed the Permian Basin, the deeper strata of which lie westward of the Central Province and thus extend under the High Plains table-land. The materials which formerly covered The Natural Regions of Texas the present surface have been stripped away by stream erosion, hence the term, Denuded Region, which was applied also to this section by R. T. Hill. The forces of denudation have acted unequally upon the variable materials of the strata exposed in the outcrops; the result is a landscape whose complex of variable features bears a direct and close relationship to the local and the general features of surface geology on the one hand and to the broader aspects of the region's physical setting on the other. Erosional cutting and local deposition continue to the present time. Much of the run-off of the Colorado, the Brazos, and the Red river systems originates in this province, and the action of the headwaters of these streams in cutting back into the High Plains along the "cap-rock" escarpment illustrates the way in which the whole province has been denuded. As indicated by the course of the streams, the region as a whole slopes southeastward. In geologic age, the materials of the outcrops and exposed sur­f aces have a great range. The hard crystalline rocks of the Llano Basin at the south are very old. The sedimentary rocks forming the inward-facing escarpments on the mar­gin of the Llano Basin are also very old. Extending south­ward to these old rocks of the Llano area is a strip of rocks of Pennsylvanian age. The outcrops of these strata are largely resistant sandstones and hard limestones; they form a dissected plateau which extends nearly to the Red river. This north-south trending plateau is cut across by the Brazos and the Colorado rivers whose entrenched chan­nels lie considerably below the level of the upland. East of this "hard-rock" plateau lie Cretaceous strata of sandy materials which dip Gulfward and whose outcrops also have a north-south trend. The thoroughly and deeply dissected Lampasas Cut Plain section, with its broad and rolling valley lowlands and its prominent rounded and ter­raced limestone hills capped by· horizontal strata of Cre­taceous age, is in this study considered in association with the several units of the North-central Plains (Central De­nuded Region). Westward from the intrenched and dissected "hard rock" plateau of Pennsylvanian age lies the Permian red-beds country. The strata af these Permian materials dip beneath the High Plains, but formerly overlying material east of the "cap-rock" escarpment generally has been stripped away. Remnant islands of Cretaceous age such as the limestone capped hills which form the Callahan Divide south of Sweet­water and Abilene, remain to show something of the former extent of these overlying materials. The Permian outcrops are composed chiefly of shales, clays, limestone, and gypsum members. These various strata are grouped into three divisions: (1) the central group made up mainly of non-resistant shales (Clear Fork beds) and whose outcrops extend from San Angelo via Abilene to the Red river lowlands and beyond the Red river into southwestern Oklahoma; (2) the eastern group underlain mainly by fairly resistant limestone strata (Al­bany limestones) ; and (3) the western group made up mainly of heavy dolomite and gypsum strata with inter­vening beds of thick sandy clays (Double Mountain beds). The various groups and members of the Permian out­crops resist erosion very unequally; the results find ex­pression in the variegated topography of the individual sections. The Clear Fork beds are mainly soft and non­resistant sandy shales. Denudation agencies produced an elongated lowland of a north-south trend with a rolling surface in the area covered by these rocks. This lowland later was partially filled in with layers of sands and silts whose flattish to slightly rolling topography has been sub­sequently and is still being modified by erosional forces. On these lands which are made up of silts and sandy silts and which possess a slightly rolling surface have developed the important farming sections which extend from San Angelo by way of Abilene and Haskell to the Red river low­lands. The Natural Regions of Texas The somewhat "hard" limestone strata comprising the eastern group of the Permian region have been reduced to a roundly rolling but deeply cut landscape. The amount of dissection and the degree of slope render this section one in which erosion is active. As results of these erosional forces, there occur the prevailing shallow soils of the section. The western group of Permian strata presents a diver­sity of features. The thicker dolomite and gypsum mem­bers are resistant to erosion; they produce the various rather rugged eastward-facing escarpments which are very marked in this section. Like the other members of the Permian country, these escarpments have a general north­south trend. The intervening softer beds of sandy clays result in the formation of rolling plains which relative to the winding escarpment levels are well marked lowlands. Areas within these lowlands have been subject to deposition of alluvial or other fine textured materials. Such areas, as for example, the territory about Roscoe, possess a rolling surface, and many have been developed as centers of farming operations. The Red River section of the North-central Plains is essentially a rolling plains country which has been sub­jected to the deposition of a variety of sands and silty materials. This section includes recent alluvial deposits along the streamways, wind-blown sandy surfaces, and the remnants of old stream terrace deposits. South of the Red river zone and north of the zones cov­ered by the Albany limestone and the hard-rock Pennsyl­vanian formations occurs a rolling country covered with sandy clays and shales. This section is a mixed farming­ranching country whereas the "hard-rock" lands southward of both Permian and Pennsylvanian members are domi­nated by ranching enterprises. Slopes adjacent to the Cretaceous remnants of the Calla­han Divide in the southern parts of the Central Denuded Region are composed of outwash materials. Where un­modified by erosional forces these smooth slopes are excel­lent farm lands, as in various areas south of Abilene. THE TRANS-PECOS COUNTRY The trans-Pecos country in Texas presents a striking. array of contrasts in the variety of its physical environ­ment. Physiographically, it is made up of rough angular­featured ranges, uplands, and plateaus with intervening basins. The latter are flattish lands of smooth aspect and usually without a drainage outlet; the materials which make up the floors of these basins have been carried in by numer­ous streams from adjacent highlands. The highland units include the Davis Mountains, Guada­lupe Mountains, Diablo Plateau, and numerous other less well known ranges and uplands. The Stockton Plateau is a dissected limestone upland whose horizontal strata are the western extensions of strata characteristic of the Ed­wards Plateau. A gigantic fault-block whose precipitous western face overlooks the down-dropped area known as Salt Basin to the west constitutes the Guadalupe Mountains. The Davis Mountains comprise a rugged upland capped by thick layers of lava rock. Erosion and dissection have sculptured these upland materials into their present varie~ gated forms. The Diablo Plateau is a vast upland bordered by the low­lands of the Hueco Bolson to the west, and the Salt Basin to the east. Portions of this plateau are covered over by loose alluvial materials deposited by the action of local streams. The basin areas, such as the Marfa Plain, Hueco Bolson, Green Valley and the Pecos Lowland (Toyah Basin), are covered with deposits of loose sandy and silty materials whose depth increases towards the central or the lower portions of the individual basins. The Natural Regions of Texas NATURAL VEGETATION IN TEXAS The distribution and characteristics of the various nat­ural vegetation formations in the State are of importance for a variety of reasons. The forests in the eastern portion of the State have been and still are the bases for important lumbering and wood-working operations. The grazing in­dustries of the South Texas Plains, of the Edwards Plateau, of the trans-Pecos, and of large areas in the High Plains and the North-central Plains or Central Denuded Region are all directly dependent upon the utilization of the differ­ent native grasses and other forage plants which are char­acteristic of these various regions. Indirectly, the native vegetation in its initial and undis­turbed state was not only a significant factor in preventing or in controlling to a considerable degree the ravages of erosion, but it was in many cases a direct factor in causing the deposition of sedimentary materials from run-off waters. In still another way, the activities of the natural vege­tation in association with soil-forming processes remain very important. For instance, the black color which extends several feet in depth in many of the prairie areas is due to the activities of the native grasses. The black color is indicative of the high content of organic matter which constitutes an .important feature of the productive capacity of these soils. Most of this organic matter is due to the· decay of grass roots in the top layers of the soil. BASIC CONSIDERATIONS The natural vegetatfon formations, whether forest, grass­land, woodland, or chaparral, represent adjustments of these types of plant life to the complex of the physical environment. The forests of the eastern portions of the State occur in a humid climate. They occur also only where conditions are favorable for the rather free circulation of ground-waters in the zone penetrated by the tree roots. Outside the better drained lands of the humid sections of eastern Texas, forests do not occur on upland areas. In many areas, however, in other parts of the State exten­sive woodlands do occur, but such woodlands are usually associated with local conditions. The soil forming materials of the forested lands of the State are silts in the cases of alluvial lands, and sandy clays, or sands and clays in the upland sections. The grasslands of the State invariably occur in areas where the soil materials are fine textured and include a high content of clay. The grasslands of humid coastal portions of eastern Texas have persisted probably because of the poorly drained conditions which obtain in these flattish lands throughout a large part of the year. Outside of this area and away from the tongues of heavy­textured limy materials which extend into northeastern Texas, the grasslands of the State occur in areas whose climate is moderately humid, sub-humid or drier. But.in the regions with non-humid climates, the grasslands are the areas with fine-textured soil materials; wherever deep sands, gravelly areas or exposures of bare rock or areas with only a thin covering of soil materials occur, such lands do not usually possess the typical grasses of the region. Usually such lands possess some form of woody vegetation, such as the different types of chaparral, the "cedar­breaks," shin oak, or stunted forms of post oak or other dwarf-like deciduous hardwoods. DISTRIBUTION AND REGIONAL CHARACTERISTICS OF NATURAL VEGETATION IN TEXAS The general aspects of natural vegetation distribution and character.istics reflect adjustments of the different types and kinds of plant life to the various types of natural environmental features involved. This principle applies not only to the larger vegetation divisions of forests, wood­lands and grasslands, but also to areal sub-divisions of these larger groups of plant life, such, for instance, as the "cedar­breaks" along the eastern edge of the Edwards Plateau, The Natural Regions of Texas the longleaf pine lands in eastern Texas, the short grass on the valley plains and bolsons of the trans-Pecos country, or the tall grass areas in certain sandy sections of the west­ern High Plains. In general, outside of alluvial lands along rivers, the forests are found in the humid sections of the State, the tall grasses grow in the moderately humid regions, and the short-grasses have developed generally in the sub-humid regions. Local features in the natural environment, as has been noted, are reflected in local adjustments of the vege­tation to these features. It is true also that the natural vegetation reacts upon and profoundly modifies many other features of the natural en­vironment such as soils, run-off and erosion. Forests of Eastern Texas The longleaf pine fores ts of the southeastern portion of Texas are well known. These forests occupy rolling lands of slight relief which are characterized by the predominance of deep sandy soils-a top soil of fine sandy loam or very fine sandy loam which grades into a subsoil of fine sandy clay. Most of this area is cut-over land, but remnants of the original forest attest the luxuriance and natural beauty of the longleaf, the most important of the southern pines. The loblolly pine forest extends westward from the long­leaf area. The loblolly also has extended itself into the sandy margins of the interior portions of Coastal Prairies of eastern Texas. Mixed in with the loblolly pines are a number of important hardwoods such as sweet gum, red oak, and some white oak. The alluvial lands which occupy the wide valley lowlands of the larger streams in the area support a dense growth of hardwoods. Because of the long, warm growing season and the high degree of humidity, the trees of both the loblolly and long­Ieaf pine areas have a very rapid growth. In some upland localities of the loblolly region, the features of dense stand and fairly luxuriant growth are illustrated as in the case of the "Big Thicket" which centers in northern Hardin County. North of the loblolly and longleaf areas, the mixed short­ leaf and hardwood forests extend to the Red river. These forests occupy the rolling lands of northeastern Texas. The relief in the dissected "red lands" section is consider­ able but gradually assumes the nature of rolling plains to the north and northeast of the "red lands." In general, the top soils of this area originally were sandy or fine sandy loams ; the subsoil in some sections is a sandy clay-in others a heavy clay. Because of the long period during which agriculture has been practiced over a large share of this area, most of the lands have been cut over to make way for farms. How­ ever, scattered throughout the area are many sections and localities with splendid growths of forests, both pine and hardwoods. Westward from the pine areas and extending to the Prairies province is a strip of rolling plains country of con­siderable width which supports a fair growth of hard­woods. As a rule the soils of these plains have a thin surface layer of fine sands or fine sandy loams underlain generally with heavy clays. This development of hard­. woods is the southwestern extension of the oak-hickory forests of the interior portion of the Mississippi Valley. Grasslands of Texas By far the larger share of the State's area was originally covered by grass vegetation. In general, the grasslands occupy regions and areas less humid than the forested lands of eastern Texas. As a rule, grasslands the world over are characterized by a dry or less rainy period of varying length and intensity during the growing season, and almost always grass formations occupy areas whose soils are fine in texture. In cases where grasses occupy sandy lands, there is usually a clayey subsoil within reach of the grass roots. The Natural Regions of Texas The original extent of grasslands in the grazing sections of Texas was greater than at present. With the coming of ranching into the various portions of the State and the subsequent fencing of the range, fires which previously swept the plains and prairies annually were gradually reduced in extent and number. Consequently woody vege­tation was no longer killed regularly by these fires and was free to develop in areas where it could compete with the grasses. Over-grazing of the native grasses and subse­quent erosion no doubt have been of importance in many sections in allowing the further spread of the various ·woody plants. Examples of cases in which woody plants have spread within the historical period of Texas development include the thicker stands of the mesquite in the heavy soil areas of North-central Texas, the spread of various types of chaparral in the South Texas Plains, and the spread of live oak into the margins of the Coastal Prairies and on the .Edwards Plateau. The luxuriant growth in dense stands of the tall grasses of the Black Prairies was in early days a center of attention of the Texas pioneers. Across those rolling strips and undulating areas stretched a closed covering of grasses whose coarse stems attained a height of two to three feet or more and made up in large part by the well-marked Big Blue-stem and the tall, golden-headed Indian grass. The same grasses and a similar distribution occurred in the strip of Black Prairies between Austin and Uvalde via San Marcos, New Braunfels, and San Antonio. Similar in grasses and in general appearance were the black lands of the Interior Coastal Prairies and the black lands of the Coastal Prairies. A large share of the black soils originally covered by these prairie grasses long ago gave way to farm­ing, but remnants of the original grasslands of the Texas Prairies province indicate something of the original nature of these prairie lands. The tall grass formations occurred principally in moder­ately humid sections; in some cases, they extended into the sub-humid sections. Tall grasses of these species and others occurred also in other sections of the State. For instance, broom sedge and Dallis grass occurs in the light­colored sandy soils of the margins of the Coastal Prairies and in open localities in the forested portions of eastern Texas. Big Blue-stem occurs in many of the sandy sections of the High Plains country. Throughout the less humid sec­tions of the State, especially where there are heavier soils, there occurs a scattering distribution of Torrey's Beard grass. But, taken generally, the grasslands outside the Prairies were and are dominated by short grasses. Indeed, there occur at present in pasture lands throughout the Black Prairies splendid g.rowth of short grasses, particularly Buffalo grass. The principal range grasses of the short grass group include Buffalo grass, many species of the grama grasses and two or three species of mesquite grasses. Associated with representatives of these types in the vari­ous sections of the State are a number of others, of which no doubt the many species of the needle grasses are the most pernicious and least valuable. In a broad sense, the High Plains country outside the sandy areas was dominated by Buffalo grass and various grama grasses. Of the latter, Blue Grama was and still is perhaps the most striking in appearance and one of the most valuable. In the Edwards Plateau, the mesquite grasses dominate. Of these, the curly mesquite is the more valuable. The plateau districts and valley plains of the trans­Pecos are dominated by species of grama and mesquite grasses, while the rolling and dissected limestone and gypsum plains of the. Central Denuded Region are domi­nated chiefly by mesquite grasses, with scattered areas of Buffalo grass and occurrences here and there of some of the grama grasses. In the South Texas Plains, short grasses dominate the lands with heavier soils outside the Coastal Prairies zone. The sandy lands invariably support tall grasses but of The Natural Regions of Texas varying stands. However, the landscape of the South Texas Plains has been greatly modified by the development of types of woody vegetation during the past seventy-five years. Throughout the grassland provinces, certain sections originally supported woody vegetation. But no matter how much modified by events consequent upon the settlement of the range, the present and initial distribution of these woody plants is and was associated with certain exceptional features in the complex of the physical environment. Only mention can be made here of some of these examples, such as the shin-oak areas of various deep sandy soils in the southern High Plains, and in smaller sandy areas in the Central Denuded Region; the "cedar-break" lands along the denuded and dissected eastern margins of the lime­stones of the Edwards Plateau; the Eastern and the West­ern Cross Timbers which cover north-south strips underlain by non-limy sandstones; the original chaparral lands on gravelly areas of the South Texas Plains; or the woodlands of the granitic area of the Llano country. SOIL RESOURCES OF TEXAS Although it is generally admitted that the soil resources of Texas constitute one of the State's major natural re­sources, it is less generally appreciated that the large scale utilization of these highly productive resources occurring over large areas has contributed greatly to the growing importance of Texas in American agricultural production. The fundamental characteristics and the range of potenti­alities of these resources have been considered too often in the past in only a general way. Regional relationships and the environmental setting of the major soil areas of the State as well as the regional aspects of their utilization have received very little attention. When it is recognized that the soils of the forested coun­try of eastern Texas possess certain common characteristics which set them off from the soils of the other sections of the State, one group of the characteristics of the regional setting of the soil resources of Texas is placed in clearer perspective. Further, when it is clearly recognized that these soils of the forested lands are naturally subdivided into a number of areas, each with its individual character­istics, the comparative features of each area are made available for interpretation. In addition, it should be pointed out that the fundamental soil features of each of these subdivisions are clearly reflected in the character­istics of the natural vegetation and the distribution of the vegetation types which are so distinctive of the whole section. In a similar way, the soil areas and their subdivisions in other parts of the State stand out in their relationships to the environmental complex of the section in which they occur. Thus, while the Black Prairies may be regarded as a unit from the standpoint of the soil resources included, this region is naturally subdivided into several parts on the basis of the soil groups involved. The soils of each one of these groups are closely related to the environment out of which they have grown, and each group possesses char­acteristics which give it a physical as well as an economic and commercial individuality. Natural subdivisions of the soil regions of other portions of the State will be discussed in more detail in later pages. BASIC CONSIDERATIONS Soil characteristics and their areal distribution may be regarded as a summation of natural forces and conditions which are and have been at work on any portion of the earth's surface. The broader aspects as well as many of the detailed features of soil resources afle determined directly or indirectly by the climatic conditions of the region involved. Another fundamental condition is that of drainage and the circulation of soil moisture as well as the associated condition of the height of the ground water. These conditions are closely related to climate and weather on the one hand and to the physiographic features and character of the geological materials on the other. The Natural Regions of Texas Combinations of moisture and temperature conditions determine the types of weathering to which the surface geological materials are subjected, and hence the types of weathering must vary directly with the types of climate involved. The weathered substances constitute the basic materials out of which the soils of the area develop. In areas in which these materials accumulate, the materials are rearranged in layers or "horizons" largely by the trans­locating forces of the circulating soil waters. The whole of the soil forming processes and their results are profoundly modified by the plant life of the area in­volved, and vegetation features are adjustments of forms of plant life to the environmental complex of the area. Thus, the fine-textured, deeply-weathered, limy materials of the Black Prairies supported originally a dense growth of lux­uriant grasses. The deep root systems of these tall grasses continually brought up from the less weathered soil ma­terials the mineral elements so important in plant nutrition. These plant food materials were left in the upper layers of the soils and thus the action of the vegetation was a natural means of maintaining the fertility of these soils. In addition, the decay of the dense fibrous root systems of these grasses continuously added to the supply of organic matter in the soil and the resulting black color of these prairie soils is a practical indicator of their high nitrogen content. In addition, the binding power of the fibrous root systems of these native grasses plus the work of the thick stand of the grass stems above ground constituted an important set of conditions which continually served to impede both sheet and gully erosion. The results of these stabilizing physiographic factors are demonstrated in part by the generally very deep accumulations of soils and soil materials as well as by the smooth features and the rounded aspects of the topography which help to give the Black Prairies some of their most distinctive characteristics. SOIL REGIONS OF TEXAS The soil provinces and soil regions of Texas, like the climatic and natural vegetation provinces and regions, are extensions into the State of soil provinces which have an extensive development in other states. This extension is to be expected in view of the close correlations between climatic conditions and vegetational features with the major aspects of soil resources. It should be emphasized that although soils and other elements in the natural environ­ment of Texas are extensions into the State of larger divisions of these elements from outside, yet the regional and local setting in each case gives to these various elements in the various sections of the State an individuality which reflects the influences of the particular regional and local setting involved. Soils of East Texas Timbered Lands The red and the yellow soil areas of Texas east of the northern Black Prairies and north of the Brazos river are western representatives of a soils group which extends eastward through the southeastern states to the AtlantiC. The whole of this vast province is humid, and it originally supported a fairly dense forest growth. Mostly these for­ests comprised pine often of pure stands of excellent growth such as the well-known longleaf regions. In fact, outside the alluvial strips along rivers, the tree vegetation of most of these lands was dominated by pines. In Texas, however, the western margins of this humid area were covered with hardwoods. These red and yellow soil areas are generally underlain by sandy materials which may or may not contain lime or by non-limy clays. Because of the action of a combination of conditions, heavy rainfall, generally moist conditions, dissected topography, and a shallow ground-water table in association with the generally sandy materials at the sur­face, weathering forces have proceeded to considerable depths; and, as a rule, soil leaching in such situations has The Natural Regions of Texas developed to a considerable degree. In the non-limy clay areas, there has often developed an extensive mechanical translocation of finer materials from the surface into the subsoils; the result is the formation of a highly sandy sur­face soil underlain by extremely heavy and tough clay subsoils. The climatic conditions in combination with the action of the forest vegetation has resulted in the formation of only slight amounts of organic matter in these soils. Some organic materials do accumulate on the surface; these, how­ever, soon decay when the forest is cleared, or they are eroded away when the lands are put into cultivation. Some distinctive areas in the sandy sections of northeast Texas are underlain by materials high or fairly high in glauconite (potash-bearing deposits) and in lime. Because of the coarser textures of the soil materials, these soils are con­tinually being leached and weathering extends rather deeply. But in spite of the leaching and of the dissected nature of the lands, these soils are productive if not covered by sands of too great a depth. The materials high in glau­conite weather to a very deep red color which is especially marked on lands with a moderate degree of slope; these areas constitute the well-known "red-lands" af eastern Texas. These red-lands have been a center of productive farming for a long period of time ; in general, they remain productive. In farming the sandy sections, particularly the deep grayish sandy areas characteristic of the rolling uplands of northeastern Texas, commercial fertilizers are being used to an increasing extent. Among the advantageous qualities of this group of soils are the excellent physical qualities of the sandy soils, espe­cially of northeastern Texas, their high degree of worka­bility, their location in a humid climate, and their very marked response to the application of proper commercial fertilizers. Because of these qualities terracing operations and methods of soil conservation promise positive results. Also, if expedient, many of the areas can be restored to their former position as first-class timber producing lands. The University of Texas Bulletin Already in fact, utilization of second growth timber over many portions of eastern Texas is the basis of promising industries. The Prairie Soils The prairie groups of soils in Texas and elsewhere in the United States have developed under the influence of a mod­erately humid climate. In practically all cases, the prairie sections are underlain by :fine-textured soil materials which usually are high or fairly high in lime. These conditions, plus the influence of the thick stand of tall grasses, have been major factors in producing the generally rounded outlines and the subdued relief features so characteristic of the undulating surfaces of the various prairie regions and areas. The major prairie region in Texas is that of the northern Black Prairies-an extensive region underlain by Creta­ceous limestones, limy clays, marls, and shales. It extends in a broad belt from the Colorado nearly to the Red river. Another important prairie region includes the Coastal Prairies, a fairly wide strip of territory adjacent to the Gulf Coast; it extends from the vicinity of Victoria on·the Guadalupe river northeastward. Similar lands, but more humid, extend eastward from Houston and then across the Sabine into coastal Louisiana; also similar lands but less humid extend southward from the Guadalupe river. On some of the lands of the Coastal Prairies strip, leaching has progressed considerably, and the leached soils are sandy at the surface and light in color. The :fine-textured clayey soils of these prairies are usually high in lime cotent and gen­erally black in color. The whole strip of the Coastal Prai­ries is developed from the materials of the Beaumont clays -a recent geological .deposit which in its initial condition is always high in lime. That the moderately humid climate of the Prairies zone is sufficiently moist for woodland growth when other con­ditions are suitable is shown by the presence of timbered strips which lie in between the various prairie regions. The The Natural Regions of Texas best known illustration of this condition is that of the Eastern Cross Timbers, a narrow strip of timbered country which extends from the Brazos directly northward nearly to the Red river. The underlying materials of the Eastern Cross Timbers are mainly moderately indurated sandstones. These materials are non-limy; they weather deeply and the generally coarse textured soil materials allow free circu­lation of underground waters. As a result these soils are rather thoroughly leached as contrasted with the slightly leached soils of the typical Black Prairies. The leached sandy soils support a woodland vegetation whereas the natural vegetation of the non-leached or slightly leached fine-textured soils of the prairies supported a luxuriant growth of tall grasses. It should be noted here that wher­ever areas of intensive leaching occurred, whether in the Prairies or in the sub-humid province, a woody vegetation of some sort constituted an important element of the native plant covering. The species of the woody plants typical of these leached soil areas are the same as or closely akin to the species of the hardwood fores ts of the central Missis­sippi Valley, whereas species of woodland vegetation such as the mesquite which are typical of the prairie soils are sub-tropical in origin. West of the Eastern Cross Timbers and extending to the sandy lands which now mark the transition to the sub-humid zone is a grassland reg\on known as the Grand Prairies. It has a moderately humid climate but is less humid than the northern Black Prairies. This region is underlain in part by "hard" limestones which resist erosion. Streams cutting through these resistant strata have created a dissected topography with more abrupt features and much greater relief than is characteristic of the rounded features and widely rolling topography of the northern Black Prairies. But, wherever conditions are suitable for fairly deep accumulation of soil materials as along the lower por­tions of long slopes, such areas have developed rich black soils typical of prairie soils in general. Soils of Sub-Hu1nid Grasslands The soils of the sub-humid climatic zones possess certain characteristics which set them off from the soils of other portions of the State. On the one hand, the soils in all humid regions are being leached-that is, circulating waters passing through the soils and soil materials carry away in solution substances which constitute food-materials to the growing plant. The rate and degree of this leaching effect varies with the features of the whole complex of the areal and regional environment, including the temperatures and length of the frost-free season, the amount, kind and time of occurrence of rainfall, the heighth of the ground-water table, the tex­ture of the soils or soil materials, especially the presence or absence of clays or sands in dominating amounts, and with the occurrence of certain chemical compounds in the soil and soil materials. In Texas, the humid regions have generally been sub­jected to much more severe leaching than have the moder­ately humid regions. In both the humid and moderately humid divisions of the State, areal and local differences have modified and, in the case of the typical prairie areas, have practically prevented leaching. On the other hand, in the sub-humid climates, leaching seldom occurs to any marked degree unless the soil ma­terials are non-limy sands without clay. Instead, associated with the lower rainfall, there is, instead of leaching or removal of constituents, a constant accumulation of the mineral nutrient materials in the soils and soil materials. This accumulation is usually reflected in the very noticeable accumulation of lime (calcium carbonate) in the soil sec­tion, and the greater the amount of active moisture present, the deeper is the lime accumulation as a rule. In the South­west, the indurated lime appears in the form of a rock layer and constitutes the typical caliche of southern and western Texas. For example, it is the thick layers of caliche The Natural Regions of Texas which constitute the "cap-rock" of the escarpment at the eastern edge of the High Plains. Grasses constitute the generally dominant natural vege­tation of sub-humid climates; the height of the grasses and thickness of stand vary directly with the amount of soil water available. However, most sub-humid grasslands possess some form of woody vegetation, and in the Texas sub-humid zone the original and present distribution of woody vegetation varies with the local distribution and dominance of what may be designated non-typical condi­tions. An example of such a situation is the well-known "cedar-breaks" which dominate the eroded and nearly bare lime-rock areas that occur along the eastern margin of the Edwards Plateau. Because of the grass vegetation in association with the factors of a sub-humid climate, the soils of such regions possess a high content of organic matter. Those, regions the world over which may be regarded as typical represen­tations of this environmental complex constitute the famous and highly productive "Black Earth" lands such as the Black Earth of the steppes of Russia, the black cotton soils in the northern portion of Peninsular India, the wheat lands of the southern Pampas of Argentina, and the hard wheat regions of the Great Plains province in the United States and Canada. In Texas, what may be correctly designated as the southern Black Earth soils occur in the High Plains, in the Abilene-Haskell Plains of the Central Denuded Re­gion, in the southern Black Prairies strip which lies in the South Texas Plains just below the Balcones Escarpment, in the sub-humid section of the Interior Coastal Prairies and in the Coastal Prairies of the Corpus Christi and Lower Rio Grande regions. Because of the climatic setting in which the soils of this sub-humid grasslands province occur and out of which many of their major characteristics have grown, the very forces which have made it possible for these soils to be so high in the chemical materials that give high fertility have also imposed limitations upon their productivity. These limitations are those of lower rainfall and occasional droughts. By recognizing these facts and the possibilities of proper management and use of methods of conservation of moisture, the farmer and rancher can do much to allevi­ate the negative effects of these conditions. In fact, farming and ranching or all other groups of economic enterprises by recognizing the power of the advantageous factors of the area or region involved and by making proper adjustments. to the region's environment have been able to carry out their operations highly successfully in every section of the State. Western Texas is no exception. Power machinery, which is so excellently adapted to the surface environment there and which allows the farmer to take a maximum advantage of the rainfall occurring during the summer, has made possible the agricultural conquest in an efficient manner of a very large share of the High Plains country during the past two decades. Because of the stages of dissection represented in the. various areas and regions of the sub-humid province and of the resulting physiographic features, a large share of the lands, especially in the Central Denuded Region, have· not developed typical "Black Earth" soils. The lands in which typical "Black Earth" soils have not been formed are generally used for grazing purposes; where well-managed,. such lands produce excellent forage. SUMMARY OF CHARACTERISTICS OF THE DARK-COLORED SOILS OF TEXAS The basic characteristics of the typical soils of the Prairie and sub-humid provinces are as striking as they are important. These characteristics may be briefly out­lined as follows: 1. The organic matter of the decayed grass vegetation is concentrated in the upper portions of the soil and may extend to considerable depths, as it does over large areas of the Black Prairies region. The high content of the· organic matter incorporated into the soil substance gives the characteristic black color to these soils, and the degree of blackness is a practical indicator of the nitrogen content. 2. These soils all have been and the typical ones are at present high in lime content. Along the eastern margins of the Prairies province, the lime content is often lower and in some cases has been entirely removed from the surface soil. The presence of the lime content constitutes a very significant factor in effecting the incorporation of the high amounts of organic matter in the soil. This fact is a very important one to consider in any program of in­creasing soil productivity, especially in the Black Prairies region. 3. The presence of the generally high lime content in all these soils indicates in a significant manner the fact that very slight leaching has taken place because it is well known that, in soil leaching, lime, if present, is one of the first materials to be carried away. And it is also generally recognized that under conditions such as prevail in Texas a high per cent of lime is indicative of a high or fairly high content of the other mineral constituents which are so important in giving to a soil its properties of fertility. Hence the necessity of recognizing these basic conditions in the laying out of programs involving either local farm management problems or agricultural policies of broad scope. 4. A fourth important factor is that of texture and the characteristics of the geological materials from which the soils have been formed. As a rule, the typical "Black Earth" and Prairie soils are fine in texture, being domi­nated by silts, silty clays, and clays-that is, by materials generally high in content of colloidal substances. These fine­textured materials under normal conditions are highly suc­cessful in resisting the forces of leaching even in a humid climate. The colloidal complex is also significant because of its power to absorb and thus retain in the soil the chemical compounds which constitute the bases of plant food ma­terials. 5. The structure of the typical black land soils in Texas and elsewhere is of great importance in determining its qualities of productivity. Typical black land soils have a surface layer which is highly grandular and thus friable and mellow. This structure condition is the result of soil substance adjustments to the environmental conditions in­volved. For instance, the factors which make for the development of granular conditions in soils are associated with the reactions of fine-textured materials high in lime and high in organic matter to recurring wetting and drying out. These granular conditions of the surface soil not only allow good aeration, free circulation of moisture, and allow ready penetration by the expanding root system of plants but they also are very important in maintaining a high degree of workability of the soils in farming operations. 6. Associated with the direct effects or the inter-rela­tions of all the foregoing factors and conditions are the crucial features of moisture capacity and availability. A soil highly granular at the surface is porous and thus will allow free penetration of water until saturated. The fine­textured materials plus the organic matter gives to such a soil a high capacity to absorb and retain moisture-that is, these things serve to intensify the sponge-like effect of soils. The retention of moisture in the soil in close asso• ciation with soluble plant food materials should serve to increase the content of these substances in solution in the soil moisture. When these soils are saturated, the granular condition disappears and the result is a sticky mass unless considerable sand is present. But as soon as drying begins, a normally developed black-land soil immediately starts to granulate and crumble. This condition may serve to give a higher degree of availability to the soil moisture, and it is practically certain that the mulch-like effect of this granular surface layer does serve to reduce loss of water by evaporation. 7. The effective working together of all the factors of the black-land soils in the regional setting in which the The Natural Regions of Texas individual soil areas occur gives to these soils not only high production capacities but also the power of maintaining these capacities with proper management for a long period of time. The high productivity is attested by data on crop yields; and in localities where these soils have been farmed for long periods of time they have shown under good man­agement a remarkable power to retain this productivity. SOILS IN RELATION TO TOPOGRAPHIC FEATURES AND GEOLOG­ ICAL MATERIALS, ESPECIALLY IN WESTERN TEXAS Considered from a broad standpoint, soil conditions and characteristics are determined largely by the climatic forces under which the soils have developed; however, physiog­raphy and geological materials constitute important fac­tors in the local and regional environment in which these climatic factors operate. Physiography and geological ma­terials determine to a very important degree the reaction of the soil materials to the climatic forces involved in the area or locality. The influence of the reactions of climatic factors to physiographic conditions and to geological ma­terials while well illustrated throughout the whole of Texas is of especial importance in all portions of the State west and south of the Prairies province. West and south of the Prairies province, all of the better soil areas and regions are on lands which have a constructional topography-as, for instance, the table-lands of the High Plains, the Coastal Prairies, the southern Black Prairies, the Abilene-Haskell Plains, and all of the valley plains or bolsons of the trans­Pecos country. The lands with a constructional topography possess deep accumulations of soil materials as well as the smooth surface features, whereas lands with an ero­sional topography usually have at the best, only shallow soil materials and are characterized by rough surface con­ditions. Hence, it is obvious that erosional areas with steeper slopes and less depth of soil materials not only absorb much less moisture during rains but retain only small quantities for periods between rains as compared with the smooth areas having deep soils of the construc­tional lands. In addition to the topography and the depths of the soil materials, the porosity and water-holding capacity of soils and of geological materials are of very great significance. The effects of variations in the texture of the soil materials are very strikingly shown in sections of the High Plains. Areas with deep sand underlain with a clayey subsoil even on the western portions of the Texas High Plains are suitable for the production of corn crops because of the capacity of such soils to absorb and retain practically all of the rainfall. Lands on the High Plains with a moderate content of sand are considerably more drought-resistant than are the fine-textured soils that are characteristic of many areas of the eastern High Plains. OIL, NATURAL GAS, AND OTHER MINERAL RESOURCES Without question, mineral resources in Texas have at­tained a commanding position in the present stage of economic development in the State. Problems of economic importance and of the commercial aspects of the diversified minerals of the State can only be briefly outlined here. It is essential to note that the large-scale development of oil and more recently commercial utilization of natural gas for a wider market have introduced a new and very sig­nificant element into the economic life of Texas and of the Southwest. Oil and Natural Gas REGIONAL FEATURES The broader features of the physical setting of these various resources with reference to the major sub-surface regions and divisions of the State has not received the general attention merited by the importance which these resources have already attained to date in Texas. That the utilization of mineral resources in general and of oil a·na The Natural Regions of Texas natural gas in particular will have an even greater im­portance as major elements in the economic expansion in the State in the near future is unquestionable. The eco­nomic aspects associated with the utilization of thes~ resources have already taken on an areal expression and without doubt developments in the immediate future will further accentuate the importance of areal and regional growth and distribution, whether the developments involved include large production, the concentration of refining operations, the extensions of oil, natural gas or gasoline pipe-lines, or less direct reactions that may come from increased utilization of these resources such as future city expansion, or the growth of individual enterprises depend­ent upon further expansion of the mineral industries of the State. Moreover, it is becoming obvious that the re­gional setting of the sub-surface f ea tures involved is sig­nificant not only from the point of view of the location of the producing areas of petroleum, for example, but is important also in getting a better line on the total avail­able reserves, as well as a better understanding of inter­relationships of the different producing horizons, the quality of the oil, and the types of production equipment, storage, and refining requirements. SUB-SURFACE RELATIONS Looked at from a broad standpoint, it is possible to sep­arate the State into two major divisions of petroleum pro­duction on the basis of the sub-surface features involved. These divisions correspond roughly to that of the Coastal Plain and the remainder of the plains-landscape of Texas. The petroliferous province which corresponds with the Coastal Plain is a vast section whose strata dip gently Gulf­ward. In a territory as large as this division, it is to be expected that major variations occur which bring about deviations from this general dip of the various strata; these variations may be directly structural or they may be asso­ciated with variable conditions under which the sediments involved were deposited. It is with certain of these major variations that oil and gas accumulations are associated. Westward from the Coastal Plain and lying eastward from the Rocky Mountain and Basin-and-range physiographic provinces is an extensive geo-syncline, or great structural basin, which extends with breaks or modifications from the northern Plateau of Mexico northward under the Great Plains province and under portions of the Interior Low­lands province. Some of the many deviations from the basin characteristics in the geological make-up of this vast territory are composed of mountainous elements which appear above the surface of the lands; such elements include the Wichita and Arbuckle mountains of Oklahoma and the Glass Mountains of Texas. Other deviations include buried ridges, buried hills, and even buried mountains. Examples of these elements in Texas include the buried Amarillo Mountains, the Red River ridge, the Bend Arch; in Okla­homa, the buried structures of Cushing, of Seminole, and of the Oklahoma City fields ; and in Kansas, the buried Nemaha Mountains. Other elements of deviation in this extensive structural basin occur at the surface-that is, erosion has stripped away the overlying strata and thus exposed the structure of what is called the Llano Uplift in central Texas and the Marathon Uplift west of the Pecos in Brewster County. Gulf Coast Fields The Gulf Coast fields in Texas occupy a zone of country some 150 miles wide which extends along the coast of the Gulf of Mexico from the Sabine river to the Rio Grande. The discovery well of the famous Spindletop which was brought in in 1901 started the development of oil production -in this well-known section of the Gulf Coast. Many other large and long-lived producing areas have been developed in this section since the spectacular Lucas gusher at Spin­dletop turned attention to this portion of Texas as a possible great oil-producing district. Among the fields which were brought in shortly thereafter are such well-known ones as Humble, Sour Lake, and later, West Columbia, Goose Creek, The Natural Regions of Texas and Sugar Land. Although the earlier of these fields defi­nitely initiated large production in Texas, the Gulf Coast fields have been able to expand production continuously and to maintain the lead in total production to date over that of any other petroliferous district of the State. The early production in these fields was from shallow horizons; the Lucas gusher came in at a depth of 1,139 feet with a flow of 75,000 barrels a day. In 1926 oil was found in deep lateral sands at Spindletop which initiated deep production in the Gulf Coast fields; in 1929 high production was at­tained in both Barbers Hill and Humble at depths of from 5,200 to 5,500 feet. From the center of this older producing area fields both shallow and deep have been developed east­ward into Louisiana and southwestward to Corpus Christi. Oil was discovered in the Refugio gas field in 1928 and large production has been maintained to the present. Other fields in this district, such as Pettus and those of the Corpus Christi area suggest potentialities in this section of the State. Because in this section oil is usually associated with salt domes, the term Salt Dome district has usually been applied to it. Interior Coastal Plain Fields The Interior Coastal Plain fields embrace a variety of geological conditions which have permitted the accumula­tion of oil in commercial quantities. Oil was discovered at Corsicana in 1896. Discovery of large production late in 1920 at Mexia opened a period of exploration and dis­covery which was extended in that area into the large fields of Powell and Wortham. The accumulation of oil in this area is associated with faulted structures as is the produc­tion in the Luling, Salt Flat, and Darst Creek fields farther south. Because of the importance of the faulted conditions of the sub-surface strata, these areas are usually referred to as the fault-zone fields. Smaller fields lie between the two areas mentioned ; and farther southward near Laredo are the Mirando and associated producing fields. In the latter part of 1929, oil was discovered at Van, a new field in Van Zandt County. The Interior Coastal Plain fields include a section in northeast Texas which has been termed the Interior Salt. Dome area ; only one of these interior salt domes, Boggy Creek, produces oil. This area, however, belongs to a deep structural trough which lies between the Cretaceous out­crops to the west and to the north, and a large sub-surface domal structure which extends into northeast Texas from. northwestern Louisiana; this domal structure is designated as the Sabine Uplift. Oil has been produced in northwest­ern Louisiana since 1902, and in recent months the explora­tion activities on the western margin of the Uplift both in Gregg and in Rusk counties have resulted in the discovery of what now appears to be a major field of production. The Waskom and Bethany gas fields in Harrison and Panola counties, respectively, are also on the western margin of the Sabine Uplift. North-central Texas The producing fields west of the Coastal Plain are usu-­ally classed under two main divisions : North-central and_ Western Texas. Each of these is further subdivided. The· North-central fields include those that lie along the Red river, including such fields as Electra, Burkburnett and Petrolia-fields associated with the buried structures of the Red River ridge-and the fields of the Bend Arch. The· Bend Arch district lies between the Red River ridge district to the north and the Llano-Burnett Uplift to the south.. The Ranger field was the first of the Bend Arch fields to. be developed; following its discovery in 1917, such fields. as Breckenridge, Desdemonia, and many others were· brought in. Western Texas In 1918, gas was discovered in the Amarillo area and in 1921 oil was discovered in the same district. This was the first producing area from the region underlain by the The Natural Regions of Texas Permian Salt Basin-a vast structural basin which under­lies much of western Texas and which extends across west­ern Oklahoma into western Kansas. Large production, however, was not attained in the Amarillo area until 1925. The productive area has been extended considerably since that date. In addition to oil and gas, the area is noted for its production of helium. Subsequent drilling has revealed the vast size of the Amarillo gas reserves. In 1923, the Big Lake field was discovered in the southern margin of the Permian Salt Basin; others which have followed in rapid succession in the development of large production in this district in Texas were such fields as McCamey, Yates, McElroy, and Hendricks which are located along the south­western margin of the Permian Salt Basin. These fields are located in zones associated with buried ridge-like struc­tures ; on the eastern margin of the Salt Basin occur ridge­like structures with which are also associated oil pools. Late in 1928, deep production was brought in at Big Lake at a depth of 8,520 feet. Other Mineral Resources In addition to oil and natural gas, Texas possesses a number of other important mineral resources. In this bulletin only a brief summary of these can be presented. Helium, as already noted, occurs in considerable quantities in the Amarillo area. In the salt dome fields of the Coastal Plain, common salt, gypsum and often sulphur occur in commercial quantities as components of the dome structure; in many of these cases, at least, large quantities of these minerals occur. In West Texas large deposits of salt and gypsum (or anhydrite) occur; commercial development of gypsum resources of the Double Mountain formation of the Permian has given rise to a considerable industry. In the southern portions of the Permian Salt Basin occur con­siderable quantities of potash minerals; along the south­western margin of this basin these deposits exist at a relatively shallow depth in zones overlying the buried structural ridges with which the oil accumulations are associated. Other mineral resources include the various quarrying, cement, brick, and tile raw materials which constitute the bases of important industries. Minerals of lesser general significance, though of local importance, such as Fuller's Earth, glass sands, and asphalt rock are found. Road ma­terials of various sorts are found well distributed over the State. Extensive deposits of lignites occur in belts along· the interior portions of the Coastal Plain in the State. Water, though commonly not thought of as a mineral resource, is one of the most important of the natural re-­sources of the State; it is important, not only as precipita-. tion, but in the form of river waters for irrigation, under­ground waters for irrigation, and for municipal supplies. A variety of metal resources are found in the trans-Pecos country-including silver and mercury. Iron ores, includ­ing magnetite in the Llano area, and the "blanket" deposits of limonite which cap certain hills and ridges in north­eastern Texas add to the State's supply of mineral resources. PART III NATURAL REGIONS OF TEXAS Because of the size of Texas and the great variety of natural conditions displayed in its various sections, it is obviously desirable to divide the State into regions and sub-regions on a scientific basis. Such regions and sub­regions, properly delineated and adequately described, will serve as necessary units in analyzing economic development and business conditions of the various sections of the State. The various natural regions and their subdivisions are shown in the Natural Regions Map of Texas (Figure 20). The detailed key-map (Figure 19) accompanies the Natural Regions Map and the Legend, all of which are in the pocket at the end of the bulletin. BASIC CONSIDERATIONS The factors which determine the delineation of the State into its natural regions are those of the physical geography of its various sections. It is obvious to even a hurried observer that the State is divided naturally into a number of sections, and that each of these divisions possesses a combination of characteristics that effectually stamps an individuality of its own upon each of these regions and areas. Analyses of the factors constituting the physical geography of each of these regions reveal fundamental inter-relationships not only between the various factors of the physical environment but also between the combination of the factors of the physical environment and the extent, quality, and availability of the natural resources of each region. In fact, it is the distribution and inter-relation­ships of the physical conditions of the regional environment which determine largely the economic aspects of the natural resources involved. It should be obvious that an analysis by regions of the Texas natural environment and its natural resources is necessary in order to get a comprehensive and well-balanced view of the potentialities of the State as a whole. Briefly, the bases upon which the surface divisions and subdivisions of Texas are made are those of moisture con­ditions. Moisture relations and moisture conditions are determined not only by the total amount and the distribu­tion through the year of the rainfall of the area involved but also by the disposition of this rainfall after reaching the earth's surface. The amount evaporated is related directly to the temperatures involved. The run-off portion varies with the type of rainfall, the porosity of the soil, the degree of moisture saturation of the soil, and the type of topogra­phy together with its vegetative covering. The disposition of the moisture which gets into the surface materials is affected by such factors as the porosity and retentiveness of the soils, of the soil materials, and of the surface geo­logical materials as well as by the height of the water-table and the type ·of topography involved. Thus, rainfall and physiography (the land-forms, geo­logical materials, and ground-water factors) are the funda­mental conditions involved in the delineation of the natural regions and of their subdivisions in Texas. These same factors give to these regions and areas their principal surface characteristics. Sub-surface characteristics, with which the oil and gas and most of the other mineral resources of the State are so closely associated, are also very closely related to the physio­ graphic divisions of the State and thus are directly and indirectly connected with the distribution of the natural regions of Texas. The territory embraced in the State of Texas has been divided by natural factors into four large divisions or provinces, each of which is further divided into a great number of regions and sub-regions or areas. The Prairies province may be taken as a starting point in making an introductory summary of Texas regions. The term Prairies province is applied to this division because of the dominance of prairie vegetation throughout the The Natural Regions of Texas greater portion of its territory. It includes the well-marked and important northern Black Prairies, the Grand Prairies, the Coastal Prairies, and the Interior Coastal Prairies. These prairie regions originally were characterized by tall grass vegetation and at present are characterized by their black soils and rolling landscape underlain by fine-textured limy materials. Lying between the prairie regions are timbered strips whose light colored soils are underlain by non-limy, sandy materials. The best known of these sandy, timbered strips is the Eastern Cross Timbers. Lying east of the Prairies and extending into Louisiana and southwestern Arkansas is a large province character­ized by a greater humidity than the Prairies province. Most of this province is timbered and is often designated as the East Texas timbered country. The coastal strip, low and flattish, wet and poorly drained, is a grassland country -a section of the Coastal Prairies which extends eastward through coastal Louisiana to the Mississippi Lowlands. Timber is the characteristic vegetation of the wide alluvial lands bordering the streams which extend across these grasslands. The interior dissected regions are practically all timbered lands. The whole province east of the Prairies including the dissected East Texas timbered country and the flattish humid Coastal Prairies may be designated as the East Texas Plains. West of the Prairies is a vast province whose sub-humid climate gives to its extensive subdivisions certain important homogeneous conditions. This province includes four major subdivisions, each of which is marked by a considerable diversity in natural conditions. The four major sub­divisions are: the eastern High Plains, the North-central Plains, the Edwards Plateau, and the South Texas Plains. Still farther westward are a number of well-defined regions which include the western High Plains, the Pecos Lowlands, the Stockton Plateau, together with the moun­tain ranges, plateau uplands, and tke intervening basins (or bolsons) of trans-Pecos Texas. EAST TEXAS PLAINS The East Texas Plains are unlike the rest of the State in that they possess a humid climate; and because of the high humidity in association with the physiographic con­ditions, the natural vegetation is forest except in the flat and low zone of the Coastal Prairies where soil and drain­age conditions generally have rendered the conditions un­favorable to forest growth. Even in the Coastal Prairies forest vegetation is coming in on the sandy lands along the margins of the dark-colored soils. The total rainfall in the East Texas Plains ranges from forty to fifty inches a year; the moisture conditions, however, vary not only with the total amount of rainfall during the year but also with the amount of evaporation, the porosity of the soil and sub­soil, and the height of the ground-water table. Considered from a broad point of view, the different areal aspects of the distribution of moisture relationships form the basic features upon which the East Texas Plains are divided; in turn, these same factors form the bases for the further subdivisions not only of that portion of the State but of all the other provinces of Texas. The primary divisions of the East Texas Plains are: (1) the low, flattish, poorly-drained Coastal Prairies and (2) the higher, dissected sandy and clayey lands which extend from the northern Black Prairies eastward and which lie north of the Coastal Prairies. With the Coastal Prairies may be included the very low, wet, marshy lands adjacent to the coast. The Coastal Prairies proper may be subdivided into (a) the black lands with the unleached or slightly-leached limy clays and (b) the light-colored areas along the margins of the black lands. The light-colored soils usually have a sandy surface under­lain with a heavy, tough clay subsoil. Usually the sandy top soils are thoroughly leached and the impervious clayey subsoils (the result of trans-location processes whereby the clayey substances of the surface materials have been carried downward by the action of circulating soil waters and deposited in the subsoil) obviously render under-drainage very slow and difficult. The rice growing districts of Texas and Louisiana occur on lands of this nature. The East Texas timbered country includes a considerable share of the East Texas Plains. These lands lie entirely in a humid climate; but the eastern half is more humid than the western, and the heaviest rainfall occurs in the southeastern corner of the East Texas Plains. The tim­bered country of the interior is sufficiently elevated to have been rather thoroughly dissected throughout, but nowhere do areas exist which possess great relief. The degree of relief varies from area to area; the lands adjacent to the Coastal Prairie strip are rolling and possess but slight re­lief; this condition holds also for the marginal plains (A-2) 1 lying just east of the Black Prairies; the greatest relief occurs in the central portions of the province in the "red lands" sections in Rusk, Cherokee, Smith, Anderson, and Nacogdoches counties whereas eastern, northern, and south­ern areas have only a moderate degree of relief and possess a generally rounded and rolling topography. Hence the East Texas Plains can be subdivided on the basis of moisture conditions or on the basis of topographic features and variations in relief of the different districts. A glance at the different types of vegetation which naturally developed in and became adjusted to the differing environ­mental factors of the various areas in this portion of the State suggest an obvious basis for still another group of divisions. However, topographic conditions in the various areas show close relationships to the geological materials as well as to the elevation and the geologic age of these materials. Even a hurried trip through this portion of Texas with casual observations of the soils reveals out­standing contrasts among the soils of the various areas. Casual observation will reveal also the obvious relationships between the different soil areas and the types of natural 1The various subdivisions of the key map of Texas are designated as (A-1), (A-2), (B-1), etc. vegetation characteristic of that area. Detailed examina­tion, however, reveals the close relationships of the soils of the East Texas Plains to the whole environment complex of the various areas-to climatic factors, geologic mate­rials, ground-water conditions, topographic forms and to the natural vegetation. For the purposes of this study the following natural regions of the East Texas Plains are delineated and their major environmental features ana­lyzed. N1ortheastern Texas comprises regions designated as A-1, A-2, A-3, and A-4. South of this group lie regions A-5 and A-6, while the subdivisions of the Coastal Prairies are designated as A-7 and A-8. Gulfward from the Coastal Prairies lie the low swampy lands which extend to the water's edge. The territory comprising regions A-1, A-2, A-3, and A-4 is underlain by the older formations of the Coastal Plain. It has the highest elevations in the East Texas Plains, and its geological structure is considerably different from that of the other portions of the province. At the north lie out­crops of strata of the Cretaceous age; these strata dip southward under the younger formations. The geological formations which outcrop eastward of the margin of the Black Prairies dip eastward and southeastward under younger formation, but outcrops of these formations appear at the surface in the region A-4. That is, these strata dip under what is structurally a basin and are exposed eastward where brought to the surface by the positive structure which is called the Sabine Uplift. This structural basin is sometimes called the East Texas syn­cline, but is perhaps better known as the Interior Salt Dome region of Texas. With reference to the location of oil and gas structures, the Interior Salt Dome region lies between the northern fault zone fields and those associated with the Sabine Uplift, which lies in extreme northeastern Texas, northwestern Louisiana, and southwestern Arkansas. Region A-3 may well be designated as the Interior Dis­sected Plain of eastern Texas. The materials at its surface The Natural Regions of Texas are the dissected outcrops of strata of formations deposited in the structural basin (Interior Salt Dome Region) ; A-2 and A-4 are plains formed by the erosion and bevelling across of strata which outcrop on either side and to the north of the Interior Dissected Plain. The materials underlying the rolling plains of regions A-5 and A-6 are outcrops of strata which dip Gulfward and those underlying A-7 and A-8 are the youngest of the Coastal Plain province. To sum up: the surface features and structural conditions of the East Texas Plains are complex; furthermore, their complexities have been increased by geological and other events since their deposition. Some of these subsequent factors include the formation of salt domes, the erosional features consequent to dissection and subsequent develop­ments such as soil formation, and the secondary concen­tration of iron ores on some of the "plateau" margins as in A-3. INTERIOR DISSECTED PLAINS, AND THE MARGINAL PLAINS OF NORTHEAST TEXAS The region comprising the Interior Dissected Plains (A-3) is underlain by sandy materials and by sandstone strata possessing various degrees of consolidation. Some of the sandy materials possess a fair to high content of glauconite (greensands, high in potash compounds) and may have a high content of limy materials. Because of the heavy rainfall and of the porous nature of the sandy soil materials, as well as of the underlying geological ma­terials, leaching is severe; and, except on those slopes where constant erosion progressively removes the soil ma­terials, the soils are generally leached. In addition to the initial high sandy content of the geolog­ical materials, the subsequent trans-location of the finer textured materials from the surface to the subsoils has resulted in the formation of soils characterized by deep gray sands at the surface underlain with subsoils of sandy clays on those rolling or flattish areas where physiographic conditions are stable enough to permit these processes to work unimpeded. The general result of the activities of erosional forces acting on the outcrops of the geological formations has been to produce a gently sloping, widely rolling topography through which streams have cut in some cases deep chan­nels; and in those cases where a resistant surface stratum exists, a deeply dissected surface with steep slopes and flattish-topped plateau-like hills is the characteristic topo­graphic feature. These more deeply dissected lands are the areas underlain by glauconitic materials, and they con­stitute the "red-lands" of the East Texas Plains. The Interior Dissected Plains region was originally for­ested and has at present a considerable amount of timbered areas. The characteristic forest trees are shortleaf pine, red oak, sweet gum, with post oak also on the eastern and western borders. The soils of the region bear a distinct relation to the topography. On slopes where erosion is active, the weath­ered geological materials occur at the surface. Areas whose surfaces are stabilized physiographically are characterized by deep, light-colored sands underlain by yellowish sandy clays. Transitional types of varying degrees of develop­ment occur between the erosional and the stabilized areas. The mineral resources of this region comprise such min­erals as iron ore, oil and gas, and salt. The iron ores, which are secondary deposits, cap the margins of the plateau-like remnants which characterize the eastern and southern por­tions of the region. The deposits are known to be shallow but not enough detailed exploration work has been done upon them to permit more than a guess at the total re­serves. Because of the location of this region overlying the Interior Salt Dome basin, oil and gas reserves there deserve much more in the way of detailed studies. Bordering the northward extending tongue of the Dissected Plateau Re­gion are the Rolling Plains strips of regions A-2 and A-4. Region A-2 lying between the Black Prairies and the Interior Dissected Plains ( A-3) is a slightly rolling country of subdued relief. The major share of this region is dom­inated by a sub-stratum of non-limy clays whose outcrops cover this zone. The non-limy nature of these clays ren­ders them very different from the limy clays so character­istic of the Black Prairies, and their fine texture sets them off in sharp contrast from the coarse sandy materials of the Interior Dissected Plains. As in the case of the In­terior Dissected Plains, a large share of the land has been cleared of its timber, but this region originally supported a hardwood forest of moderate-sized post oak timber together with some gum and hickory. The soils are light in color; the top soils are sandy with varying amounts of clays, but the subsoils are generally heavy clays. The presence of these dominating features of sandy surface and clayey subsoil is due largely to the results of translocating the finer materials from the sur­f ace and depositing them in the subsoil, this translocation having been accomplished by the work of percolating water in the soil and apparently aided by the chemical reactions of substances present in the soil materials. The sharp break between the surface soil and the subsoil is charac­istic of the whole region. A smooth surface and gentle slopes are characteristic of homogeneous layers of finely textured surface materials. These f eatures of slight relief and gentle slope combined with the heavy subsoils often render drainage slow and difficult. Region A-4 is the Texas section of the lands overlying the Sabine Uplift, and in some ways it is similar to A-2. It has, however, important differences. The geological sub­stratum generally has a high content of sandy materials, but much lower than the substratum of the Interior Dis­sected Plains. Not only are the clay members more sandy, but the members high in glauconitic materials are more extensive in area in A-4 than in A-2. Associated with the conditions of less clay and greater sand content, the surface of the lands of A-4 is more deeply dissected and thus has a greater degree of relief with steeper slopes than is char­acteristic of the topography of A-2. The relief factors possibly constitute reasons for the smaller proportion of farm land in this region as compared with that of A-2. A large share of the region is covered with hardwood timber together with some shortleaf pine. The soils possess factors in common with regions A-2 and A-3 although they have also important differences. Because of the greater preva­lence of erosional topography, deep sands are less char­acteristic of the surface soils of A-4. Because of the smaller clay content, translocation forces of percolating waters have not produced the heavy, tough, impervious subsoils so characteristic of A-2. Instead, the upper portions of the subsoils of A-4 are crumbly and hence better drained. Be­cause of the better drainage, this portion of the subsoil is better oxidized; hence the prevalence of reddish subsoils in contrast to the yellowish subsoils of A-2. The timber growth of this region is marked by the thick­ness of stand, and the vigor of the vegetative growth of the individual trees. This vigorous growth is associated with the heavy rainfall and the relatively high qualities of the soils of the region. THE ROLLING PLAINS The Rolling Plains lands of the southern section of the East Texas Plains lie between the dissected zone of "red lands" at the north and the flattish Coastal Prairies at the south. These plains are designated as A-5 and A-6. Region A-6 is a slightly rolling country generally, and formerly was dominated by luxuriant longleaf pine forests; this dis­trict may be appropriately referred to as the Longleaf region. A-5 is a region with more variable characteristics, and lies to the west of the Longleaf region; it supports a good growth of loblolly pine, gum, and other hardwoods. On account of the moist conditions in combination with the long and warm growing season, timber growth is rapid in these two regions. Moreover, a large proportion of each The Natural Regions of Texas region is in timber or is cut-over land. The cut-over land is especially noticeable in the longleaf region; in the loblolly region ( A-5) , even though the rainfall is less, the stands replace themselves naturally and readily. The differences in natural replacement between the two regions are asso­·ciated with fundamental differences in the respective re­ gional environments. This Rolling Plains country which comprises A-5 and A-6 is underlain by strata of clays and sandy clays whose out­crops in general parallel the Gulf Coast. Their general topography is that of gently sloping lands of slight relief whose elevation gradually rises interiorward from the flattish Coastal Prairies to the fairly rugged and dissected escarpment which marks the transition between these rolling plains and the Interior Dissected Plain Longleaf Pine Region The Longleaf pine region (A-6) is a gently rolling coun­try which extends from Louisiana across the Sabine river "into the southern portion of eastern Texas. The underlying geological materials have a high sand content. The sand content of the surface soil has been greatly increased by ·soil-forming forces in which the action of translocation ·forces which have removed the clayey materials to a great depth in this surface soil. The result is the formation of these very deep sandy soils which even in this climate com­monly dry out to considerable depth during the summer season. At a depth of several feet these sands grade into sandy clays which are moist or wet during the greater part of the year. The longleaf pine seedling with its very long tap-root enables the tree to get started under these condi­tions, whereas the seedlings of other trees do not possess such root adjustments and therefore such seedlings com­monly die when the sands dry out during the summer sea­son. Hence, in the typical longleaf pine areas no other trees were found in association with these pines. When the Iongleaf lands have been cut over, it is obvious that other trees come into these typical longleaf areas only with difficulty. Under present conditions even the longleaf replaces itself in these typical areas only very slowly; this slowness of replacement is due chiefly to the ravages of fires and to hogs. However, if immediately after being cut over, the lands are protected from both fires and hogs, the longleaf naturally and readily replaces itself. In areas thus protected the second-growth trees grow rapidly, and, if the stand is close, tall trees with straight and clean trunks are as char­acteristic of the second growth as of the original forests. Loblolly Pine Region As a consequence of its more westward location, the Loblolly pine region (A-5) has a somewhat lower rain­fall than has the Longleaf region. It is also subjected to stronger winds during a greater part of the year. The less rainfall and the greater evaporation have important consequences. In reality, the western margin of A-5 mainly supports an oak vegetation. The lessened supply of mois­ture at the western margin no doubt makes the conditions there less desirable for the growth of pine forests. In addition, the underlying geological materials apparently are less sandy. This condition is very apparent in the geolog­ical formations outcropping in the interior sections of A-5. For example, the Jackson and Yegua formations in addi­tion to their high content of clay also possess certain chem­ical compounds which react to increase the rate and degree of translocation of the finer materials from the surface soil to the subsoil. The result is the formation of a very tough and intractable subsoil which is overlain by a layer of fine sandy material of varying depth, but usually not of more than a foot in thickness. HUMID COASTAL PRAIRIES The Coastal Prairies regions as a whole stand out in sharp contrast to the dissected lands interiorward. Geo­logically they are young and their surface is dominated by constructional f eatures. Because of their geological youth and slight elevation, very little erosion has occurred on the The Natural Regions of Texas Coastal Prairies. What erosion has taken place is found mainly in the interior zones of the prairies, whereas the coastward zones are flattish and appear generally to be without any surface irregularities. Because of the humid climate to which the eastern por­tions of the Coastal Prairies are subjected together with their low elevation, the lands of regions A-7 and A-8 are wet, and an important problem of their future utilization is that of adequate drainage. Coastward, the prairie lands grade into the low and wet coastal marshes which are char­acteristic of this portion of the coastal country. The poorly drained conditions of these lands apparently have been an important factor in keeping out forest vegetation and in allowing certain grasses to come in. Forests do occur on the wide alluvial flats along the streams which cross the prairies; and forest trees, especially loblolly pines, are advancing into the interior margins of the prairies. The natural conditions of the forested lands, however, cannot be regarded as typical of those of the prairies proper. The soil characteristics of the humid Coastal Prairies reflect the conditions of the environment out of which these soils have developed. In general, outside of the marshes and the river alluvial lands, three soil groups are distin­guishable. These groups include: (1) the black soils of the interstream flat sections of the prairies; (2) the light­colored soils which lie along the interior margins of the prairies and adjacent to some of the drainage ways; and (3) transitional soil areas which occupy positions somewhat intermediate to those of the black soils and of the light­colored soils. The geological materials underlying the Coastal Prairies are clays which usually possess a slight content of sand but whose lime content is high. Two factors acting upon these clay materials have brought about the development of the major characteristics of the soil resources. The black soil areas which are dominant in A-8 represent con­ditions in which a high content of organic matter has been incorporated into the soil materials because of the decay of large quantities of grass roots in these soils. Invariably these black soils are high in lime up to the surface, and in the typical black soil areas the effects of leaching appear to be slight or negligible. The light-colored soils of the Coastal Prairies on the other hand are as a rule highly leached at the surface, although the subsoil materials usually are high in lime. These soils are characteristic of A-7. Most of these light-colored soils are covered with grasses, but the general features of the natural vegetation are considerably different from those of the typical black soil areas. It is upon these light-colored soils that the forest vegetation is steadily encroaching. The surface of these light-colored soils is highly leached as a rule. While the thorough surface leaching is associated with the heavy rainfall, another condition apparently has been the determining factor in accentuating this form of development. Apparently certain chemical compounds in soil materials of these leached areas have resulted in the deflocculation of the clay particles. When these clay ma­trials are in a deflocculated condition, they are free to be translocated by the action of percolating waters. As a result, the clay particles are removed from the surface soils, which brings about characteristic sandy conditions of the surface soil. The deftocculated clay particles are car­ried down to and left in the subsoil. The result is to in­crease greatly the clay content of the subsoil. This condition is responsible for the formation of the tough, intractable subsoil conditions so characteristic of the light-colored soil areas of the Coastal Prairies. By way of contrast it should be noted that the presence of lime in the typical black soils of the Coastal Prairies results in a flocculated condition which resists the trans­locating action of the percolating waters. The soil groups transitional between the light-colored highly leached soils and the unleached, black soils, are on areas which have begun to leach; hence, these soils do not possess the intense dark color of the typical black soils, but The Natural Regions of Texas they retain a content of organic matter sufficient to give them a dark color. Likewise, translocating influences have been at work in these soils sufficiently to develop a well­marked subsoil, but not a heavy, intractable subsoil that is characteristic of the thoroughly leached soils. The rice districts of Texas and Louisiana have developed on Coastal Prairies lands which have a well-developed sub­soil. Rice is grown in some of the thoroughly leached soils where certain conditions are favorable; however, the leached soils of the Coastal Prairies are mainly in pasture. The black soil areas provide excellent pasturage, and are characterized by a considerable agricultural development. The transitional soil areas are the most suitable to rice pro­duction as a rule; they possess sufficient fertility for excel­lent vegetative growth; the presence of the heavy subsoil prevents the rapid percolation of the irrigation waters; their generally flattish surface is well adapted to irrigation and to large-scale mechanized agriculture. THE PRAIRIES PROVINCE The Prairies province of Texas is characterized par­ticularly by tall grass prairies in contrast to the predomi­nantly timbered country eastward and the predominantly short grass and stunted timber or chaparral country south­ward and westward. Widely rolling and undulating black land prairies of slight relief with smooth or rounded surface features