MINERAL VARIETIES OF PROPYLITE. 257 



burst formed narrow dykes, which often stand up in bold remnants 

 thirty or forty feet above the surface. The texture sometimes becomes 

 fine, compact, and fissile, like hornblendic slate, where it is in con- 

 tact with diorite. Propylite is more easily decomposed than any other 

 volcanic rock, forming white, yellow, and red clays. North of 

 Tuscarora it is overlain by rhyolite. In the Toyabe range, near 

 Boone Creek, hornblende propylite is overlaid by rhyolite and basalt. 

 At Kaspar's Pass, north of Hot Spring station, at the S.W. of 

 Montezuma range, the propylite is also covered by rhyolite and 

 basalt. At Berkshire Canon, propylite lies to the east of a lofty 

 mass of melaphyre, and is invaded by quartz-propylite and andesite, 

 and overflowed by trachyte, which in turn is covered by rhyolite, 

 succeeded by basalt. 



Minerals in Propylite. The green hornblende of propylite is 

 frequently changed into epidote, a change which is never seen in 

 the brown hornblende of andesites. Frequently the felspar crystals 

 are filled with hornblende material, which is changed into bright 

 yellow epidote in the Washoe country. Apatite occurs in short 

 thick rounded prisms, having a hexagonal section. In Sheep Corral 

 Canon the propylite is grey, and in the Truckee and Montezuma 

 ranges the low hills of propylite have a yellowish green-grey colour. 

 In the Fish Creek mountains of Nevada, the hornblende is composed 

 of aggregates of green microliths ; and augite occurs which is re- 

 markable for its pale-yellow colour; brown mica and apatite are 

 found. In Storm Canon the rock is pale yellow and reddish grey. 

 The hornblende in andesite never exhibits the parallel staff structure 

 seen in propylite. At Tuscarora, in the Cortez range, green and dark- 

 brown hornblende occur together. 



Quartz Propylite. In that part of the Cortez range which lies 

 south of the Humboldt river is a mass of propylite, with quartz 

 propylite resting upon it and forming the summit of Cortez peak. 

 At Papoose Peak the quartz propylites again come to the surface, 

 extend for about eight miles, and then pass beneath overlying dacite. 

 The general colour of the surface is soft grey, pinkish and salmon 

 colour, varied with green and olive hornblende. The ground mass 

 consists of clear dark plagioclase, more or less fibrous hornblende, 

 microscopic quartz, with fluid cavities sometimes including cubes of 

 salt. The hornblende has the prismatic staff-like form characteristic of 

 the propylitic rocks. There are the usual titanites. The larger 

 felspars are all dull and slightly kaolinised. At Waggon Canon the 

 rock contains a few laminae of brown mica. Biotite seems to be 

 characteristic of the latest injections. Quartz propylite has the aspect 

 of having been erupted in an almost solid condition, showing no 

 tendency to spread out into thin sheets. According to Zirkel, one of 

 the finest exhibitions of this rock is in Berkshire Gallon, Virginia 

 range ; the ground mass is grey, rich in macroscopical crystals of 

 dark-green hornblende, and dust of hornblende in laminae, crowds all 

 the larger felspars. In some localities apatite is present, and occa- 

 sionally there is a little sanidine. The rock at Cortez peak, seen 

 VOL. I. B 



