EAST HUMBOLDT EANGB. 533 



plentifully, extending lengthwise with the direction of the mica; they are 

 sometimes flattened, and are occasionally bt'oken, appearing in disconnected 

 sections. Hornblende is entirely wanting. The most interesting charac- 

 teristic is the microscopical crystals of zircon. 



A little way down from the summit on the west side of White Cloud 

 Peak, a change takes place in the rock, and the granite becomes overlaid 

 apparently unconformably by a series of quartzites and hornblendic schists, 

 which occupy the range to the western foot-hills, sinking under the over- 

 lying Pliocene beds. North of the granite body, these overlying schists 

 curve around and occupy the entire width of the range, which they con- 

 tinue to do to its northern extremity, where it passes under the valley of the 

 Humboldt River. They have a westerly dip, varying from 20° to 45°, and 

 toward the base of their series present a somewhat granitoid appearance. 

 This immense thickness of gneisses and crystalline schists contains a few 

 beds of white dolomitic limestone occurring in beds from 1 to 6 feet in 

 thickness, separated from each other by micaceous quartzites and mica- 

 schists. The whole limestone series has only been observed in one or two 

 localities on the summit of the ridge, at Mount Bonpland and Clover Peak, 

 and is altogether embraced within a band of less than 60 feet thick. Over 

 the hmestones are further micaceous schists, and above these, forming the 

 summit of the series, is a heavy development of quartzite. These quartzites 

 form the summit of the ridges, which slope from Clover Peak westward. 



The erosion of glaciers has excavated deep U-shaped canons, which 

 have cut through the quartzite, leaving it standing upon the lateral ridges, 

 and exposing the lower schist series in the bottoms of the canons. These 

 quartzites are very well developed along the upper waters of Boulder Creek, 

 and also in Clover Canon. On Plate XIX, this erosion of pure quartzite by 

 glacial action is well shown, exhibiting the steep escarpments of the summit, 

 the narrow lateral ridges, and the manner in which the brittle rock splits up 

 with a sharp angular fracture. 



The quartzites of Clover Cation are either white or stained a light yel- 

 lowish-brown by infiltrated oxide of iron. They consist mainly of white 

 quartz, which is at times milky and at times translucent in the same speci- 

 men. They also carry garnets up to the size of a large pea, numerous 



