CAMBRIAN AND LOWER ORDOVICIAN. 77 



Mr. Ulrich reports that the fossils obtained from the El Paso limestone in both the EI Paso 

 and Van Horn quadrangles represent essentially the same Beekmantown fuana. Most of the 

 species are undescribed, but all are of unmistakable types. The more characteristic forms are 

 the following: 



Calathium sp. nov. (coral-like sponge), Maclurea? sp. noT. The small hornlike opercula 

 are very common. The shell itself is of the type of M. oceana Billings. SoHd siphuncles of 

 endoceratoid cephalopod, evidently a close ally of Cameroceras irainardi. Besides these there 

 are a number of less easily recognized small gastropods. 



H 14. LLANO DISTRICT, TEXAS. 



In Mason, Llano, and Burnet counties, Tex., the pre-Cambrian rocks are 

 unconformably overlain by Upper Cambrian sediments. Shumard ^^^ originally 

 described the section. During 1908 and 1909 detailed surveys have been carried 

 out by A. C. Spencer and Sidney Paige, and the following description is abstracted 

 from notes furnished by them. 



UPPER CAMBRIAN. 



The Upper Cambrian of this area is essentially the equivalent of the Reagan sandstone 

 in Oklahoma, agreeing with that formation not only in age but in lithologic succession. 



The Cambrian sediments rest upon a complex of metamorphic rocks which include schists, 

 gneisses, and enormous masses of granitic intrusives. 



The Cambrian beds have been divided into three formations, namely, from the base upward, 

 the Hickory sandstone, the Cap Mountain formation, and the Wilberns formation. 



Conglomerate and sandstone reaching a maximum thickness of about 250 feet constitute 

 the lower formation. Following, but with a gradual transition from sandstone to limestone, 

 are beds consisting predominantly of limestone, capped by 15 to about 75 feet of cross- 

 bedded glauconitic sandstone. These strata, about 90 feet thick, constitute the second for- 

 mation. The third formation includes limestones and shales from 170 to 220 feet thick, the 

 shales occupying approximately the upper third of the formation. 



The following section is characteristic of the lithology of the formations, though the thick- 

 ness of the basal beds varies considerably, owing largely to the unevenness of the pre-Cambrian 

 floor. 



Section of Hickory, Cap Mountain, and Wilberns formations on Packsaddle Mountain. 



Feet. 

 Grayish slabby, slaty crystalline limestone; very little glauconite; more massive beds toward top 



of peak 40 



Thinner-bedded crystalline limestone; some glauconite 20 



Heavy-bedded pink limestone, somewhat oolitic; contains some glauconite 10 



Yellow and white sandstone with small percentage of glauconite, grading up into pink sandy 



limestone 14 



Glauconite sand and coarse quartz sands; iron concretions on surface 6 



Massive-bedded grayish-brown crystalline limestone, somewhat oolitic; glauconite increasing 



toward top 35 



Flaggy subcrystalline limestone with small amount of glauconite ; yellowish discolorations 30 



Grading into purer limestone. Several red bands of sandstone alternating with beds of hard 

 subcrystalline limestone and fine-grained whitish sandy limestone; crystalline limestone con- 

 tains some glauconite grains 35 



Thin-bedded calcareous dirty-white sandstone, grading upward into very fine-grained hard 

 reddish-brown sandstone. Weathers rough but generally shows a brown sand on surface. 

 Broken surface shows reddish-brown sandstone with crystalline faces of calcite. Makes cliffs 

 which weather irregularly and show bands of red, yellow, and dirty-brown cross-bedded sand- 

 stone alternating with very calcareous beds _. 200 



Ledge of calcareous sandstone, conglomeratic and containing a few shell fragments, also few glau- 

 conite grains 2 



Massive and thin-bedded red and yellow sandstone, with some shale, probably covered 35 



