THE OVERLAND EOUTE OGDEN TO SAN FRANCISCO, 157 



and the development 

 railroad. More comi 



m 



logical Survey 



.ypical ol the Great Uasm; in 



elements 



intervening vaUey plains. In the mountains probably the most 

 conspicuous rocks are the Tertiary lavas^ although a full series of 



sedimentary beds is also present, as well as great masses of intrusive 

 igneous rocks of various types. The rocks may be briefly mentioned 

 in the order of age. (See table on p. 2.) The pre-Cambrian basal 



rocks 



ocks in 



lavas rest, are visible in a few places. East of a line passi 



east of Winnemucca through Austin to a point a little wes 



Paleozoic strata are the predominating sedimentary 



mountain ranges, which include few or no Mesozoic beds. The 



enormous thickness of the Paleozoic section at Eureka (almost 30,000 



feet) sugtrests that the shore line of the Paleozoic sea was somewhere 



near this place. Tliis is further indicated by the fact that west of 



rocks disaDDear and 



Triassic 



During the 

 from Avhich 



sediments were washed into a sea on the east. In Mesozoic time the 



to have been reversed. The Jurassic and Triassic 



eems 



sediments were apparently derived from a land area of uplifted 

 Paleozoic strata in the eastern part of the State. The Triassic lime- 

 stone, slate, and sandstone and the associated lavas of the Humboldt 

 Ean^e have an estimated thickness of 10,000 feet. Somewhat similar 



more 



in this region during 



ediments 



have been found in Nevada, and it is therefore supposed that the 



asm 



small bodies of granular 



such as may be called gi'anite (including quartz monzomte, grano- 

 dioritc, and similar rocks), extend from the great masses in the Sierra 

 Novad a to the eastern part of the State or beyond. All these bodies may 

 be more or less related; they appear to be younger than most of the 



sediments but older than the Tertiary rocks 



Cretaceous 



as 



m 



?over large areas, some ranges being e 

 areas in the vallevs are covered wi 



gravelly deposits of streams, with materiixl laid down in lakes, or wi 



durinir volcanic eruptions 



The movements by which the mountains and vaU^ 

 formed probably occurred in different periods, but it i 

 most of them broke and shifted the sheets of Tertiary 



