THE COMSTOCK LODE. 17 



a gateway to the Carson Desert. The whole configuration of the surface is 

 one massive pile of hills, steeply sloping into deep, narrow ravines. 



As the description proceeds, it will be seen that the topography owes its 

 characteristic forms and its rapid changes of slope to the great variety of 

 rocky material. Indeed, there is scarcely a more interesting example, within 

 the limits of the exploration, of the complete subordination of surface form 

 to geological structure. 



At the western edge of the map, and a little to the north of its center, is 

 a mass of syenite, bounded upon all sides by a more recent volcanic rock, to 

 wdiich Baron Richthofen has given the name of propylite. 



Propylite occupies the broad zone from north to south through the cen- 

 ter of the map, broken by chains of outci'ops of andesite, which have burst 

 through it on lines approximately parallel to the summit of the range. In 

 the southwest corner is a complicated association of metamorphic rocks, 

 overflowed first by quartz-propylite and, more recently, by outbursts of 

 basalt. At the deepest part of American Canon, and at the lowest exposure 

 of metamorphic rocks, is a small outcrop of granite, the only occurrence of 

 this rock nearer than the summit of the Pine Nut group. Along the east 

 side of the map, and covering nearly a quarter of its area, is an immense over- 

 flow of sanidin-trachyte. It is of this material that the high summits of 

 Mount Kate, Mount Rose, and Mount Emma, and the prominent cone of the 

 Sugar Loaf, are formed. Arranging these rocks according to their relative 

 ages, we have, first and earliest, the metamorphic rocks, uralitic and mica 

 schists and limestone, with an unimporlant accompaniment of granite; next 

 the syenite, which, with the first mentioned series, is all we have left of the 

 original Jurassic range. Superimposed upon this slope, outpoured, first, the 

 trachytic greenstone knovi^n as propylite, which, over all the upper portions, 

 was a sub-eerial ejection, but, as it approached the lowlands, was finally 

 poured out beneath the level of the great fresh-water lake which formerly 

 skirted the range. The evidence of this is to be found in the tufaceous form 

 of the propylite, which shows all the phenomena of aqueous arrangement 

 and stratification. Leaves of Tertiary plants are found in the tufa at the 

 height of about 700 feet above the present bed of the Carson River. The 

 propylite formation is of considerable orographical importance, for over a 



