THE COMSTOCK LODE. 21 



and not unfrequently tinted with the chrome-green of decomposed hornblende. 

 Occasional augitic forms, transmuted into hornblende, give it a uralitic char- 

 acter. 



From a great accumulation of evidence, gotten in other parts of the Great 

 Basin, it is believed that these metamorphic series are above the Carbonifer- 

 ous, and that the limestone is -one of the upper members of the great Triassic 

 series, which is developed on such a grand scale to the eastward. The green 

 felsite of Crown Point Ravine probably underlies the limestone, and is the 

 continuation of the same bed which overlies the granite in American Canon. 

 All the metamorphic rocks are traversed by a net-work of minute veins hardly 

 thicker than a sheet of paper. 



Syenites. — The syenites occupy the summit for the space of about two 

 miles square, just above the city of Virginia. Here is a large, bold outburst 

 of the formation, rising from the level of the town and extending back to the 

 west slope of the range. The summit of Mount Davidson is about the center 

 of the body. It is bounded upon the north by propylite, which forms the 

 northern slope of Ophir Ravine. The Crown Point Ravine marks its south- 

 western limit. Thin, dike-like ridges project still further to the south, finally 

 losing themselves under the propylite. It is really an insular mass, one of 

 the ancient original summits, which is completely surrounded by the subse- 

 quent propylite. In one of the ravines which cut the basalt divide, separating 

 American Flat from Spring Valley, is a small, obscure outcrop of syenite. 

 This, from its remoteness and extremely limited size, merits no attention. 

 The Davidson mass is in plan a rough parallelogram, rising in the center to 

 an elevation of 7,827 feet. It is cut from west to east by two sharply eroded 

 ravines, transversely to its summit line. The overflow of propylite has failed 

 to cover two narrow dikes which still outcrop on the slope of Cedar Hill. 

 These spiny ridges, together with the Spring Valley outcrop, indicate a very 

 wide extent of syenite buried beneath the later eruptive rocks. In general the 

 slopes of the syenite are smooth, although they occasionally weather in sharp, 

 fantastic pinnacles. A prominent example of this castellated structure may 

 be seen at the head of Gold Ravine, where, rising from the general slope of 

 Mount Davidson, are several groups of needles ranging from 30 to 150 feet 

 in height. 



