568 GEOLOGY 



or Wyoming, in those places where the succession of formations has 

 been studied in detail. The Helderberg is present in the Arbuckle 

 Mountains of Oklahoma, 1 and probably in southwestern Texas. 2 

 The Devonian system has little development in the Rocky Moun- 

 tains, but is somewhat wide-spread between the Rockies and the 

 Sierras, though its outcrops are not extensive. In some places, 

 as about Globe, Arizona, the system is much faulted and affected 

 by igneous rock; 3 in others it is bounded by unconformities, both 

 below and above, 4 while in still others its limits are not sharply 

 defined. The system in the west has not been generally subdivided, 

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

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

 types of fossils are found, and in overlying beds, fossils corresponding 

 to the Eurasian (rather than to the east American) faunas, have 

 been recognized. Hamilton types, with great vertical range, also 

 occur. The testimony of the fossils of the Basin region is to the 

 effect that it was not connected with the eastern interior sea in 

 such a way as to allow the free intermigration of marine life. 



The system is said to be 8,000 feet thick in parts of Nevada, 5 

 and 2,400 feet in the Wasatch Mountains; but in the Yellowstone 

 Park, 6 it is only 160 feet thick, and not divisible into distinct forma- 

 tions. In the western interior generally, limestone is the dom- 

 inant formation. 



Devonian formations are known in both northern and southern 

 California, and may be present in many places where the rocks are 

 metamorphosed past identification. In the Klamath Mountains, 

 the Devonian (chiefly Middle) is much disturbed, and contains 

 igneous rocks (tuffs and lava flows). The Devonian system is also 



1 Taff, Atoka (I. T.) folio, U. S. Geol. Surv. 



2 Hill, Physical Geography of the Texas Region, folio 3, topographic atlas, 

 U. S. Geol. Surv., p. 4. 



3 Ransome, Professional Paper, No. 12, and Bisbee folio, U. S. Geol. Surv., 

 pp. 39-46; also Reagan, Am. Geol., Vol. XXXII, p. 278. 



4 Walcott, Am. Jour. Sci., Vol. XXVI, p. 437, 1883. 



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

 X, pp. 423-432. 



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



