Fauna of the Glen Rose formation




Whitney, Marion Isabelle, 1911-

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Very little is generally known about the Glen Rose formation and its fauna. There have been several publications which included a few forms found in the Glen Rose, but none to date that deal exclusively with it. Such geologists as Roemer, Conrad, Cragin, Schltiter, Credner, Giebel, Bflse, Hill, White, Clark, Shumard, Kniker and others described Glen Rose fossils, but their works were never extensive, sometimes including only one or two forms. In some of the earlier works, species were described but not figured. This often makes it impossible to identify the species described. Where it was necessary, older classifications were changed in this paper to agree with more advanced knowledge and some few forms were renamed entirely where the nomenclature was conflicting. The Glen Rose formation varies in thickness from a few feet up to 740 feet at its outcrop in central Texas and is composed of massive, hard limestone beds in alternation with softer limestone beds. Upon exposure to the atmosphere some of the softer beds break down into clays and shaley limestone, but as has been shown by the three-foot cores at Marshall Ford dam site on Colorado River, most of the formation consists of various types of limestones. The basal portion, however, contains some sandstone. The upper 60 feet or more of the formation is very sandy. Although fossils are abundant in the lower Glen Rose, some beds, particularly the upper ones, seem to be quite barren of fossil remains. The fossils described in this paper were collected chiefly by Dr. F. L. Whitney from central Texas. A few of the forms, however, came from Gypsum Bluff near Murfreesboro, Arkansas. The majority of the specimens were found in Comal and Bandera counties, Texas. Many were collected in Blanco and Hays counties, and a few came from Kendall, Burnet, and Travis counties. The Glen Rose yields an abundance of fossils, but very few are well preserved. Such forms as Ostrea, Neithea, Pecten, and a few others have well-preserved shells, but most of the fossils are preserved as casts and impressions, which are often badly distorted. In the case of Pelecypods and a few Gastropods such as Nerinea and Nerinella it is an advantage to have some casts, where determination depends upon such internal characters as can be shown by the casts. The disadvantage, however, in having only casts with which to work is that little or nothing is known of the ornamentation of the shell. Thus it is necessary to depend largely on the form of the cast for specific determination as was done in the case of many of the Pelecypods described in this paper. In the case of many of the Gastropods the measurements of the spiral angles as well as the general form of the shell were used for specific determinations