EAVENSWOOD PEAK. 639 



I'heir general resemblance, however, points rather to the Carboniferous 

 than the Triassic formation, and they have been considered to represent 

 the Upper Coal-Measure group, while the underlying quartzites are supposed 

 to belong to the Weber group so largely developed to the north. 



An obscure outcrop of the same black quartzite is found along the base 

 of the cliffs, about midway in Eeese Eiver Canon, here dipping to the west- 

 ward, and probably corresponding to that found near the summit of the 

 ridge to the west of Ravenswood Peak. These outcrops in the neighborhood 

 of Ravenswood Peak would therefore seem to be the remnants of a sharp 

 anticlinal fold, whose axis runs a little east of north. 



Under the .Quaternary accumulations of the valley are exposed in 

 various places Tertiary beds, which have been referred to the Truckee 

 Miocene, as wherever the exposures have been such that the bedding could 

 be recognized they are shown to underlie the volcanic rocks, and to have 

 suffered disturbance previous to the volcanic period. It is probable, how- 

 ever, that there has been a Pliocene deposit in some of these valleys, whose 

 material has been too soft and loosely agglomerated to withstand erosion, 

 so that it is difficult to distinguish it from the Quaternary accumulations, 

 or from the considerable beds of volcanic ash which border the hills, whose 

 material in the field it is not always easy to distinguish from that of the 

 Pliocene. 



The rhyolites which have covered these older sedimentary and eruptive 

 rocks, and built up the present outlines of the range, present an almost 

 infinite variety of color and texture. The flows exposed in the Reese 

 River Canon are mostly rhyolitic breccias. They are sometimes a com- 

 pact, hornstone-like material, of a dark bluish-gray color, striped and 

 banded, and carrying well-defined crystals of glassy feldspar, but generally 

 no free quartz. Another form of breccia is a rather earthy, porous 

 rock, in which the feldspar crystals are largely kaolinized, but which 

 contain a great quantity of black mica, which is entirely undecom- 

 posed, the included fragments being generally of the harder hornstone- 

 like variety of rhyolite. Another rhyolite from the canon resembles micro- 

 scopically the typical porphyritic red rhyolite, having a light purple color, 

 showing some tendency to decomposition in bands. This rock under the 



