PAPPOOSE PEAK REGION. 581 



crystalline groundmass of purplish-brown tri clinic feldspar and green horn- 

 blende, in which are porphyritically enclosed earthy kaolinized feldspars, 

 less decomposed than those of Cortez Peak, aggregations of crystals of 

 green hornblende, and a few dark-brown biotites. ■ Under the microscope, 

 these latter contain between their laminae interposed layers of calcite crys- 

 tals, and apatite occurs in the groundmass and in the biotite. 



This long ridge seems to be made up of repeated outflows, which 

 have piled upon one another in thick masses, never showing the slightest 

 tendency to overflow or spread out in thin sheets. The rock has the appear- 

 ance of having been erupted in an almost solid condition, and possesses no 

 evidence of flow whatever, which is not the case in the Washoe propylites. 

 The lower exposures contain no biotites, and the feldspars and hornblendes 

 both more closely resemble the rock of Cortez Peak. The biotite-bearing 

 member is probably the last outburst, and is not represented at Cortez Peak. 

 As in the Cortez quartz-propylites, the quartz is never or rarely visible to 

 the naked eye, but under the microscope is seen to form a prominent ele- 

 ment in the groundmass. In the rocks of Pappoose Peak, it is the horn- 

 blende that has suffered more decomposition than the feldspar, while at 

 Cortez Peak the reverse is true. The actual proportion of biotite in the 

 former rock is small, but its presence is conspicuous, because the flakes are 

 very large, sometimes a quarter of an inch in diameter. The groundmass 

 is also decidedly finer than at Cortez Peak. With these minor differences, 

 the rocks are otherwise closel}^ similar. 



Lying to the east of the quartz-propylite body is a large development 

 of dacite, which extends south from Wagon Canon 8 or 10 miles, and 

 descends to Pine Valley on the east. The prominent colors are dark-purple 

 and dark-chocolate in the groundmass, in which are enclosed remarkably 

 white, decomposed triclinic feldspars and numerous black, glittering quartz. 

 Contained in the groundmass, and closely approximating to it in color and 

 general appearance, are small angular fragments thickly scattered through 

 the whole rock. These fragments contain secreted crystals of hornblende, 

 plagioclase, and quartz, which are generally smaller than those secreted from 

 the groundmass, but in other respects identical. The rock is, therefore, a 



