12 SMITHSONIAN INSTITUTION 



interpretation of which requires most detailed mapping plus careful 

 collecting of fossils from accurately determined strata in precisely 

 placed localities. These collections are used to date the rocks contain- 

 ing them and serve to determine the superposition of the strata when 

 the sequence is obscure. In such a region as this the fossils have a 

 great practical value, besides their biological significance. " 



The geologic column at Eureka includes rocks from all parts of 

 the Paleozoic era. Our interests were chiefly in those of the lower 

 half of the Paleozoic — Cambrian to Devonian. We also collected 

 Lower Ordovician fossils in the adjacent Antelope and Toquima 

 Ranges. The Antelope Range lies about 40 miles south-southwest of 

 Eureka and, like most other Basin ranges, is a tilted block. From it 

 we took many fine fossils from the middle part of the Lower Ordovi- 

 cian. In the Toquima Range, located about 60 miles southwest of 

 Eureka, we collected sponges, brachiopods, and trilobites from the 

 upper part of the Lower Ordovician. 



Our last collecting ground in Nevada was in a small range just 

 west of the Spotted Range about 60 miles northwest of Las Vegas. 

 Here the sequence includes strata ranging from Lower Ordovician 

 to Mississippian in age, all tilted to the southeast. At the west base 

 of the range, opposite Frenchman Flat, silicified Lower Ordovician 

 fossils are abundant. Blocks of this rock showing an abundance of 

 well-preserved fossils were selected to be dissolved in the laboratory. 

 This treatment frees the silicified fossils from their matrix and 

 often yields specimens preserving man}- delicate features which are 

 ordinarily lost. 



Texas. — In traveling from Las Vegas, Nev., to El Paso, Tex., 

 we collected a lot of fine L'pper Devonian fossils from soft shales 

 exposed not far northeast of Silver City, N. Mex. The fossils weather 

 free and are well preserved, and many fine specimens were obtained. 



The Franklin Mountains, which terminate just north of El Paso, 

 contain one of the type sections of Lower Ordovician rocks in the 

 Southwest. In the arroyos and road cuts at, and just west of, the 

 lookout on the Scenic Drive, which skirts the southern end of the 

 range and overlooks the Rio Grande Valley and the cities of El Paso 

 and Juarez, we collected Lower Ordovician fossils, many of them 

 similar to some of those collected near Eureka and Blacksmith 

 Fork. Among them were fragments of a second starfish of approxi- 

 mately the same age, but much larger and totally different in most 

 respects from the one found in Utah. In the Hueco Mountains 

 about 30 miles east of El Paso we collected Permian fossils while 

 on our way to Van Horn. 



