792 DESCRIPTIVE GEOLOGY. 



Hardin City Salts. 



Chloride of sodium 18.47 



Carbonate of soda 52.10 



Sulphate.of soda 27.55 



98.12 



Of the latter, Professor Allen says : "It is reasonable to suppose that 

 it contains an appreciable amount of borate of soda." 



The general level of the Mud Lakes is about that of the lowest part 

 of the Humboldt and Carson Deserts, from 3,850 to 3,900 feet above sea- 

 level, while similar terrace-lines attest the former presence of the waters of 

 the La Hontan Lake. The terrace-lines are in general more distinct on 

 the western side, where a steeper wall was presented to the former lake, and 

 later erosion has not so readily concealed them. Deposits of lacustrine 

 tufa are abundant in the Black Rock Mountains, covering some of the lower 

 outlying hills and extending through the lower passes. They are also 

 found along the slopes of the Granite Range, and in greatest development 

 along the basalt wall of the Madelin Mesa on the western side of the smaller 

 Mud Lake. 



The Black Rock Mountains form topographically a southern spur of 

 the mountain mass north of the limits of the map, whose culminating point 

 is known a-s Mount Lander, a peak of apparently 9,000- or 10,000 feet in 

 height, which is probably connected with the northern continuation of the 

 Granite Range uplift. The portion represented on the map consists of low 

 broken ridges of rhyolite and basalt, in which these rocks are found quite 

 regularly bedded, and presenting almost uniformly a bluff face to the west, 

 with a gentle slope to the" eastward, their bedding planes having as high an 

 angle as 20°. As a rule, the basalt flows form the summit of these ridges, 

 while on the Avestern bluff faces are found, at the base, the outcrops of 

 underlying rhyolites. In a few instances, however, rhyolites were found 

 again, forming the capping beds, generally separated, it is true, by intervals 

 of debris slopes from what appeared to be the underlying basalt flows. It 

 seems probable that the present structure, and perhaps, also, the apparent 



