LOWER TRUCKEE VALLEY. 821 



quartzite, the change in half an inch being almost complete from a porous 

 earthy infusorial to a compact cherty stone. 



A specimen of the brown fissile variety was submitted to chemical 

 examination by Mr. E. W. Woodward, and found to have even a higher 

 percentage of silica and less alumina than the pure white earth analyzed 

 from the Miocene Tertiary of Fossil Hill. 



The analysis yielded the following: 



Silica 91.43 91.51 



Alumina 2.89 2.95 



Ferrous oxide 0.66 0.63 



Lime 0.36 0.39 



Magnesia 0.25 0.20 



Soda 0.63 0.59 



Potassa 0.32 0.33 



Water. 3.80 3.79 



100.34 100.39 



In the delta between the two lakes arises a ridge of limestone provision- 

 ally referred to the Triassic, which extends in a northeast and southwest 

 direction nearly 3 miles, with a width from east to west of about a mile. 

 It is separated from the Triassic formations of the Lake Range by a broad 

 gap, which is filled with sand-dunes, and its assignment to the Triassic is 

 based mainly upon theoretical grounds. The limestone is highly metamor- 

 phosed, in places having been altered to a fine crystalline white marble, 

 which upon analysis yielded Mr. B, E. Brewster the following: 



Alumina 0.05 



Lime 55.16 



Magnesia 0.76 



Soda 0.39 



Potassa 0.22 



Carbonic acid 43.54 



Insoluble residue - 0.04 



100.16 



