Geology of the Honey Creek area, Llano County, Texas

Precambrian metasedimentary rocks in the Honey Creek area are divided into two formations, the Valley Spring Gneiss and the Packsaddle Schist. The Valley Spring Gneiss, the older of the two, consists chiefly of pink quartz-feldspar gneiss. The Packsaddle Schist, of which about 12,000 feet is exposed in the area, is made up of amphibole schist, graphite schist, muscovite schist, leptite, and marble and calcsilicate rock. Two types of metagranite, several small plutons of metaigneous amphibolite, and part of a granite batholith are also present in the area. The metamorphic rocks in the area attained the rank of the almandine-amphibolite facies during regional metamorphism. Most of the minor structural elements are related to a major fold system which trends northwest through the area. With few exceptions, foliation is parallel to original bedding. Two foliations, generally a bedding foliation and a slip cleavage, are present locally. A b-lineation, formed by alignment of elongate minerals, is commonly present in the Packsaddle Schist. Rarely a second lineation, consisting of small crinkles, is also present. Three joint sets - two sets of shear joints and a set of release joints - can be distinguished. The bisectrix of the acute angle between the shear sets is normal to the fold axes, and the release joint set is parallel to the axes