594 DESCRIPTIVE GEOLOGY. 



smoky, and feldspar, with a small development of hornblende. The micro- 

 scope also detects the presence of biotite,. and shows that the gronndmass 

 is made up mostly of axially fibrous strings. The rock contains few angu- 

 lar fragments of quartzite. 



At the southern end of this ridge, in Osino Canon, is exposed a section 

 of steeply-dipping quartzites and conglomerates, the latter showing the char- 

 acteristic angular fragments of cherty material of the Weber Quartzite. 

 Their general structure is that of a short synclinal fold, having a north and 

 . south axis, the beds b^ng upturned at high angles. Within the quartzites 

 are also some black, apparently carbonaceous seams. The outcrops are 

 very irregular, and are masked on the south of the river by the rhyolite 

 flows of Upriver Peak. On the north of the river, at the eastern end of the 

 canon, is a body of light-gray, very crystalline rhyolite, having almost a 

 granitic structure, containing sanidin, quartz, and mica. 



In the broad valley of the Humboldt River, above Osino Cailon, are 

 foimd in the dry season a number of saline incrustations, resting upon the 

 fine impalpable Quaternary soil. From one of these deposits near Peko 

 Station, a sufficient amount was collected for chemical investigation, the 

 sample yielding 52 per cent, of soluble alkahne salts. 



An analysis by Mr. R. W. Woodward gave the following: 



Soda 46.81 



Sodium 2.97 ' 



Carbonic acid. . . , 30.78 



Carbonic acid (excess over monocarbonate) , 10.07 



Sulphuric acid 2.59 



Chlorine , . 4.58 



Boracic acid 2.41 



100.21 

 The theoretical combination would give: 



Carbonate of soda and excess of acid , 83.57 



Sulphate of soda 4.60 



Borate of soda 4.49 



Chloride of sodium 7.55 



100.21 



