PEOPYLITES OF THE FORTIETH PARALLEL. 137 



rock is an augite-andesite, and one characteristic of the District, but is 

 partially decomposed. 



Exploration of the Fortieth Parallel. Slide No. 215, specimen No. 22,689. Crown 

 Point Ravine, Washoe. 



A very dark, somewhat basaltic-looking rock. The slide resembles 

 that last described, containing, however, only pseudomorphs of chlorite after 

 augite, and none of the fresh mineral. The chlorite and the mineral from 

 which it was derived were carefully identified in the manner indicated in 

 the last paragraph. There is no fresh hornblende, but a few very minute 

 oval rings of magnetite grains probably represent the black borders of 

 former hornblendes. The feldspars, which are not distinguishable from 

 ordinary andesitic plagioclases, contain spots which look like devitrified 

 glass-inclusions. IMiis, too, is augite-andesite. 



Esjiloration of the Fortieth Parallel. Slide No. 216, specimen No. 22,690, from Crown 

 Point Ravine, Washoe. 



This rock is much decomposed, and neither augite nor hornblende are 

 present in a fresh state, but the slide contains many black borders, which 

 retain the characteristic outlines of hornblende, though they now surround 

 only calcite, quartz, and a few residual grains of epidote. There is also 

 one good pseudomorph of chlorite after augite. From my acquaintance with 

 the rocks of the District I have no hesitation in pronouncing this a horn- 

 blende-andesite. 



Exploration of the Fortieth Parallel. Slide No. 217. Gold Hill Peak, Washoe. 



There is no specimen in the collection corresponding to this slide or 

 to the locality, which is represented on the map accompanying this paper 

 by the southern "Twin Peak". My own specimens are coarse greenish- 

 gray rocks of somewhat open texture. The feldspars are not tlioroughly 

 transparent in consequence of incipient decomposition. The fresher por- 

 tions of the mass show brilliant hornblendes. The slide contains some fresh 

 blown hornblendes with black borders, and some black borders from which 

 the bisilicate has disapjjeared. A portion of the hornblende exhibits the 

 intermediate color between green and brown, which is seen in so many 



