1922] Vaughan: Geology of San Bernardino Mountains 345 



Undifferentiated Schists 



Extending south and east from San Bernardino Mountain to the 

 San Gorgonio Pass and the lower portion of Whitewater River, and 

 thence northward to Big Meadows and Big Morongo Creek, there is 

 a great mass of contorted schists of variable character. Granite has 

 invaded this area in many places and has been so subjected to deform- 

 ing stresses that it also possesses a foliated structure and in many cases 

 cannot be readily distinguished from the schists of sedimentary origin. 



Because of their highly metamorphosed character and complex 

 folding, as compared to the quartzites and limestones north of the 

 Santa Ana River, these rocks were at first thought to be much older, 

 probably pre-Cambrian. However, certain portions of the clearly 

 recognizable sediments were found to be so altered as to be indistin- 

 guishable from the rocks, thus raising a doubt as to their relations. 

 Before discussing this phase of the problem the rocks themselves will 

 be more fully described. 



Schists are exposed in the lower portions of Smith Creek north- 

 east of Beaumont. The schistose laminae are folded and twisted in a 

 very complex manner. The principal constituents are quartz, biotite, 

 and a feldspar, but the rock is so decomposed that the feldspar was 

 not determined. The schists are intruded by a granite mass on the 

 north and are cut by apophyses of this mass. Both granite and schist 

 are cut by pegmatite dikes containing crystals of muscovite more than 

 two centimeters across. 



On the west side of San Gorgonio River, two miles from its mouth, 

 there is a peculiar rock exposed in a small gully which has cut down 

 through the overlying fanglomerate. At first sight it has the appear- 

 ance of a granite, but closer examination shows that it consists of 

 slightly rounded pieces, one to fine centimeters in diameter, of greyish 

 quartz with interstitial biotite ; and it may be an altered pebble con- 

 glomerate. This overlies a dark, medium-grained plastic rock contain- 

 ing quartz, biotite, and muscovite. Both are cut by pegmatite dikes 

 containing large crystals of pink orthoclase and varying in thickness 

 from a few inches to nearly two feet. 



On the opposite side of the canon there is a rock containing much 

 biotite presenting several variations. Near the bottom it is composed 

 almost wholly of biotite as small flakes and is without schistosity. 

 Higher up it is schistose and contains some muscovite in addition to the 



