ABSTRACTS 



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GEOLOGY. — Some mining districts in northeastern Nevada and north- 

 western California. James M. Hill. U. S. Geol. Survey Bull. 

 594. Pp. 200. 1915. 



This report embodies the results of a geologic reconnaissance which 

 had two main objects, (1) to satisfy a present public demand for 

 reliable information, and (2) to gather data which should be of use in 

 preparing at a later time a general report on the geology and ore de- 

 posits of Nevada, The report brings out many facts not only of practi- 

 cal but of scientific interest, such as the widespread occurrence of 

 adularia in the veins of northwestern Nevada, the presence of second- 

 ary tetrahedrite and wurtzite in the Reese River district, and the pres- 

 ence of selenium in the veins of Aurora. 



In the region covered, sedimentary rocks ranging in age from Paleo- 

 zoic to Mesozoic were noted. These sedimentary rocks, in practically 

 every camp in which they were noted, have been intruded by granit- 

 oid rocks ranging from diorites through monzonites, quartz mon- 

 zonites, and gi'anodiorites, to granites. Their age was not definitely 

 determined, though they cut Jurassic rocks; it is believed, however, 

 that they were all intruded during the late Cretaceous or early Tertiary- 

 period of intrusion common to the Sierra Nevada and Great Basin 

 province. Lava flows cover considerable parts of the region visited, 

 particularly along the western border of Nevada and in northeast 

 California. Farther east, in Lander County, volcanic rocks are less 

 conspicuous. 



The ore deposits are grouped as gold-silver deposits, silver-lead 

 deposits, copper deposits, and antimony deposits. Each of these broad 

 groups is further subdivided according to the mineral composition of 

 the ores and their mode of occurrence. 



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