TRUCKEE CANON. 827 



Teuckee Canon. — The Truckee Canon cutting deeply into the very- 

 core of the range, affords an opportunity for the study of volcanic outburst 

 scarcely excelled anywhere in Nevada. The entrance to the canon near 

 Glendale is an east and west gap of erosion, flanked on the north by a high 

 mass of trachytic rock rising abruptly to an elevation of 1,800 feet above 

 the river-bed, while the hills on the south are formed of an accumulation of 

 successive outpourings of andesite and andesitic breccia reaching a height of 

 1,200 to 1,500 feet, presenting a distinctly bedded appearance, and a preva- 

 lent dip toward the canon. In this group of aiidesites, there is the most 

 remarkable range of texture as well as of mineralogical composition. Solid 

 olive-gray masses occur, in which the triclinic feldspar and hornblende 

 appear distinctly in a gray micro-crystalline groundmass, and which in every 

 case appear to underlie a second series of reddish-brown and yellowish- 

 brown cellular andesites having almost the scoriaceous habit of trachj^te. 

 A remarkable feature of the rock is the presence of both hornblende and 

 augite, the latter frequently in crystals one-eighth of an inch in length. 

 According to the microscopical observations of Zirkel, the tWo minerals are 

 never present in equal proportions, but one always predominates, and the 

 other occurs as a very subordinate accompaniment. Following this mixed 

 group of hornblende and augite-andesites, and closing the series, is a mass 

 of breccia containing together angular fragments of the two preceding 

 groups, but for the most part made up of the augitic variety, with whose 

 ejection there must have been an immense accompaniment of water. In 

 some of these later breccias, the angular fragments of the earlier series 

 have been much decomposed, leaving irregular earthy masses, but carrying 

 well-defined crystals of augite. Nowhere among the andesites of the 

 Fortieth Parallel Survey is there any such approximation to the trachytic 

 texture; nowhere such a well-marked occurrence of large individualized 

 augite crystals. 



On the hills south of this andesite .group, in the continuation of the 

 range toward Mount Davidson, but lying beyond the boundary of Map V, 

 there occurs a great development of propylite, which is intersected by 

 numerous dikes of compact, gray hornblende-andesite, which here and 

 there overflows it in sheets, as at Washoe. The parallel is still further 



