436 GEOLOGY. 



rock; 1 in others it is bounded by unconformities, both below and 

 above, 2 while in still others its limits are not sharply defined. In 

 this western interior the system has not been generally subdivided, 

 and where subdivisions have been made, they have not been cor- 

 related with those of the east. In the Great Basin region, Onondagan 

 (Corniferous) types of fossils, and in overlying beds types correspond- 

 ing to the Eurasian (rather than to the east American) faunas of the 

 northwest, have been recognized. Hamilton types, with great ver- 

 tical range also occur. The testimony of the fossils of the Basin region 

 is to the effect that it was not connected either with the eastern interior 

 sea or with South America in such a way as to allow of the free inter- 

 migration of marine life. 



The system is 8000 feet (6000 feet of limestone and 2000 feet of 

 shale) thick in the Eureka district of Nevada, 3 and 2400 feet (quartzite 

 and limestone) in the Wasatch Mountains. In some parts of the 

 west, as in the Yellowstone Park, the system is thin (160 feet 4 ), and 

 not divisible on physical grounds into distinct formations. In the 

 western interior generally, limestone is the dominating formation. 



Still farther west, on the Pacific side of the Paleozoic land area, 

 Devonian is known in both northern 5 and southern 6 California, and 

 may be represented in many places where the rocks are metamor- 

 phosed past identification. In the Klamath mountains, the Devonian 

 (chiefly Middle) is much disturbed, and contains igneous rocks (tuffs 

 and flows). The Devonian faunas of the coastal region, like those 

 of the Great basin, are Eurasian in their affinities. 



The Devonian system is also abundantly represented in widely 

 separated parts of Alaska. 7 



1 Ransome, Professional Paper, No. 12, and Bisbee folio, U. S. Geol. Surv., pp. 39-46; 

 also Reagan, Am. Geol., Vol. 32, p. 278. 

 »*' 2 Am. Jour. Sci., Vol. XXVI, pp. 437-438, 1883. 



3 Geol. Expl. of the 40th Parallel, Vol. I; see also Weller, Jour. Geol., Vol. X, 

 pp. 423-32. 



4 Weed, Yellowstone Nat Park folio, U. S. Geol. Surv. 

 6 Diller, Am. Jour. Sci., Vol. 15, 1902, p. 344. 



6 Spurr, Bull. 208, U. S. Geol. Surv. 



'Brooks, Bull. Geol Soc. Am., Vol. XIII, pp. 256-61, and Professional Paper, 

 No. 1, U. S. Geol. Surv., p. 211; Schrader, Bull. Geol. Soc. Am., Vol. XIII, p. 241: 

 and Professional Paper, No. 20, U. S. Geol. Surv., pp. 62-67. 



