SEOSHONE EANGE. .|g, 621 



of the peak. That these glaciers were exceedingly short is proved by the 

 character of the canons a mile from the base of the peak, where, instead 

 of the round ship-bottom curve, they are very sharp and V-shaped, and 

 evidently the result of stream erosion. 



The dacite from Shoshone Peak has been analyzed by Mr. R. W. 

 Woodward, who reports the following composition for the rock : 



Sihca 70.17 70.25 



Alumina ...... 14.53 14.90 



Ferrous oxide 4.03 4.08 



• Manganous oxide trace trace 



Lime... 2.29 2.39 



Magnesia 0.93 0.83 



Soda 3.25 3.24 



Potassa 3.35 3.32 



Lithia trace trace 



Loss by ignition 1.53 1.51 



lOO.OS 100.52 

 Specific gravity, 2.54, 2.65. 



In this rock, the percentage of silica comes within the limits of that 

 found in rhyolites, and but little lower than the amount usually obtained 

 in rhyolites of Central Nevada. It is of special interest to note that the 

 amount of potassa slightly exceeds the soda, as it does in other dacites from 

 Nevada, as well as in many from European localities.^ The jjercentage of 

 lime, which is also low, is, however, higher than in the dacites analyzed 

 from the Washoe region. 



A little northeast from Shoshone Peak, in the bottom of a deep canon, 

 is a small inconspicuous outcrop of diorite. This diorite bears some slight 

 resemblance to the later dacite, especially in the occurrence of the numerous 

 large grains of pellucid quartz. The groundmass, however, is distinctly 

 crystalline, with a compact texture, which acts under the hammer like the 

 older rocks. Triclinic forms of feldspar predominate, associated with some 

 especially brilliant orthoclase crystals. In the groundmass are some minute 



* Microscopical Petrography, vol. vi, 136. 



