14 SMITHSONIAN INSTITUTION 



Another fine, relatively undisturbed sequence of Lower Ordovician 

 rocks similar to those at El Paso is exposed on the north end of 

 Beach Mountain, about 10 miles north of Van Horn and just east 

 of the escarpment of the Sierra Diablo Plateau. We collected at 

 many horizons in this section. 



One of the finest Permian sequences in the world is located in 

 the Glass Mountains north of Marathon, Tex. The thickness of the 

 column is rather variable, but on the average it contains between 6,000 

 and 7,000 feet of sediments, all dipping gently to the northwest. The 

 limestones, at least those in the lower formations, abound in fossils 

 many of which are well silicified and hence susceptible to etching in 

 hydrochloric acid. We worked for 4 days in these mountains collect- 

 ing from the Leonard and W r ord formations. We were fortunate in 

 obtaining many fine specimens of two peculiar brachiopods : Pro- 

 richthofenia, having the shape of a coral ; and Lcptodus, a very- 

 aberrant brachiopod having the general shape of an oyster when seen 

 from the ventral side. In Lcptodus the dorsal valve consists of a 

 series of narrow parallel-sided lobes extending laterally from a cen- 

 tral axis. These lobate extensions fit over transverse parallel grooves 

 extending laterally along each side of the central line inside the 

 opposite valve. 



After leaving Marathon we went to the Central Hill country of 

 Texas to Mason and Llano. In the vicinity of these places we col- 

 lected Cambrian fossils needed in the collections and also studied and 

 collected from the Lower Ordovician Ellenburger limestone which 

 is the partial equivalent of the El Paso limestone and of formations 

 studied farther north and west. 



In Jacks and Palo Pinto Counties west of Fort Worth we col- 

 lected Pennsylvanian fossils weathered from shales and limestones 

 well exposed in these counties. Mrs. J. H. Ren fro and her daughter, 

 collectors of Pennsylvanian fossils, took Cooper to two fine localities 

 where many good specimens were obtained. 



Oklahoma. — -The Arbuckle Mountains and Criner Hills in south- 

 central Oklahoma are low hills exposing a fine Paleozoic sequence. 

 Here the Simpson group of the Middle Ordovician contains many 

 fine fossils. We collected brachiopods and a few crinoids at several 

 localities. 



White Mound, a famous locality for Lower Devonian fossils, is a 

 small bare hillock of disintegrating argillaceous limestone. It lies 3 

 miles west of Nebo, Okla., and about half a mile north of the county 

 road. The fossils, which are extremely abundant, weather free from 

 the enclosing limestone and can be picked up from the surface of the 



