360 University of California Publications in Geology [ VoL - 13 



grey, all in well-defined beds. Some of the bedding planes exhibit a 

 distinct sheen resembling schist. Fractures are common in all direc- 

 tions, some of which are filled with quartz containing cubes of limonite 

 pseudomorphic after pyrite. 



Between Baldwin Lake and Round Valley the quartzite, with its 

 interbedded strata of biotite and muscovite schist, has been intruded 

 by pegmatite, biotite and hornblende lamprophyres, and granites. As 

 is usually the case, the extremely acid and basic rocks occur as rather 

 limited dikes. Some of the granite has a marked gneissic structure, 

 and, as this is parallel to the sehistosity of the surrounding rocks 

 regardless of the shape of the intrusive mass, it is clearly due to defor- 

 mation since solidification, rather than to the flow of intrusion. There 

 are also large irregular masses of biotite granite which retain the 

 original structure. The quartzite itself presents many phases. Some 

 is very pure quartz without a trace of bedding. From this extreme 

 there is a gradation to well-bedded pure quartz varieties, then quartz 

 with muscovite or biotite or both, and finally to a muscovite-biotite 

 schist. 



There is a small area of quartzite south of Bear Valley. The 

 whole slope is forested and, as is usually the case in country of low 

 relief, no solid outcrops of quartzite could be found, but the hillsides 

 are covered with angular fragments. Many of the low ridges just 

 south of Pine Lake are almost free of soil, but even here no solid out- 

 crops were seen. 



Another small area is found southwest of Holcomb Valley. It 

 appears to dip beneath the limestone and it may be that both are over- 

 turned. They are intruded by granite to the west. 



One of the interesting features of the quartzite is the way in which 

 it has been affected by deformative forces and the intruding granite. 

 It has already been noted that some of the impure strata have been 

 rendered schistose, and even in some of the pure varieties a distinct 

 sheen can be seen on the quartz grains parallel to the" bedding. East 

 of Baldwin Lake the general dip is 40° southwest, and this is uniform 

 throughout a considerable portion of the mass. But locally, particu- 

 larly near granitic intrusions, these beds have quite a different char- 

 acter. They are crumpled and folded in a very complex manner and 

 the rock itself resembles more nearly a granitic gneiss than sediments 

 (fig. 2). This is a matter of considerable importance, for it shows 

 that extreme alteration and complexity may not necessarily indicate 

 greater age than more simple rocks even within a restricted area. 



