814 DESCEIPTIVE GEOLOGY. 



Lake Range. — This range, M'hicli measures about 50 miles in length, 

 rises out of the arid plains of the Mud Lakes, and, continuing southward, 

 divides the waters of Pyramid and Winnemucca Lakes. Its peaks attain an 

 altitude of between 3,000 and 3,500 feet, with a base not more than 6 miles 

 in width, the steep slopes on both sides reaching down to the water's edge, 

 where they are fringed by a narrow border of Quaternary gravels and cal- 

 careous tufas. 



Granites and Archaean rocks occupy a large area at the northern end 

 of the Lake Range, and, but for the occurrence of small outbreaks of basalt 

 that protrude through the granite and skirt the flanks on both sides, the 

 entire upper portion of the mountains might be so referred. They extend 

 in a north and south direction, with unbroken continuity, for over 30 

 miles, rising above the adjoining valle3^s in a very irregular ridge, culminat- 

 ing in Pah-rum Peak. South and east of Pah-rum Peak, the granite falls 

 away rapidly, and is soon concealed beneath heavy beds of dark shale, 

 which have been provisionally referred to the Jurassic age, while to the 

 southwest basalts cover the older rock, extending to the shores of Pyramid 

 Lake. Wherever this granite body was observed, it possessed, in texture, 

 color, and physical habit, the general features of those of the Granite and 

 Truckee Ranges. 



At the extreme northern end of the range, extending out in a long 

 tongue toward the northwest, occur a number of low, rounded hills, of a 

 characteristic gneissic formation, which possess some interest, as it is quite 

 unlike any other observed rocks in Western Nevada. It is to be regretted 

 that time did not permit of their being more fully studied and their con- 

 nection with the granite more satisfactorily made out. In their superficial 

 habit, as shown in their mode of bedding, their action under atmospheric agen- 

 cies, and arrangement of mineral constituents, these gneissic beds resemble 

 closely the so-called primitive gneisses, but in mineralogical composition, even 

 to the detailed microscopical structure, show a striking analogy to the pre- 

 dominant granite bodies of Western Nevada. They possess a very distinct 

 gneissic structure, witli the brown mica arranged in parallel planes through a 

 fine admixture of feldspar and quartz. In color, they are brownish-gray. 

 The feldspars are exceedingly fine, but, under the microscope, are shown to 



