816 DESCEIPTIVE GEOLOGY. 



lying east of Pyramid Lake considerable bodies of older rocks may occur 

 which have not been covered hj the last of the volcanic products. 



Basalts usually dipping slightly to the eastward form the extreme 

 southern end of the range. In general, they resemble those described from 

 the Truckee and Virginia Ranges, including both the fine-grained compact 

 rock and the highly cellular porous variety. One specimen from this 

 locality resembles the grayish-black rock found in the hills south of the 

 Kawsoh Mountains, having the same horizontal lenticular cavities lined 

 with the lilac-colored siliceous coatings. Brilliant acicular crystals of 

 plagioclase characterize the rock, and are the only well-developed minerals 

 observed. One other variety of basalt from here deserves mention, being 

 quite unlike the surrounding rocks, and, under the microscope, is shown to 

 be wanting in glassy base, although in other mineralogical and structural 

 features resembling the normal basalts. 



