1922] Vaughan: Geology of San Bernardino Mountains 347 



ing in size from two to a hundred feet across. These rocks are usually 

 ellipsoidal in form, but sometimes have one or more flat boundaries. 

 Both granite and inclusions are crossed in all directions by pegmatite 

 dikes from an inch to two feet thick. The whole rock mass has been 

 repeatedly faulted. 



On the south side of San Bernardino Mountain the schists strike 

 west of north and dip 30° to the northeast. They are very hetero- 

 geneous, some being biotite schist with a few grains of magnetite and 

 a decomposed feldspar, while other parts are rather high in quartz 

 and are granitic, although this is somewhat masked by schistosity. 

 At the peak there is a great deal of biotite schist having a silky, 

 crinkled-ribbon appearance. On the east side of the peak there is a 

 peculiar occurrence. A fine-grained biotite granite lies between schists. 

 In the schist next to the granite there is a layer, about a foot thick, 

 consisting of angular fragments of schist, granite and pegmatite all 

 firmly held together by the granite. Lower down on the ridge epidote 

 is to be seen everywhere. 



The rocks around San Gorgonio Mountain exhibit great complexity. 

 Medium-grained, biotite granites are found grading into distinctly 

 schistose masses. These are intruded by granite with tongues branch- 

 ing into the schist. This sort of thing can be found on nearly any 

 scale, some distinct apophyses being only a few inches thick and less 

 than two feet long. The masses of schist in the granite are relatively 

 small, only a few inches to a few feet across. A specimen from near 

 the peak appears to consist practically wholly of biotite flakes about 

 two millimeters across in parallel arrangement, but a microscopic exam- 

 ination reveals a few flakes of muscovite and scattered grains of mag- 

 netite, as well as a few grains of quartz containing small needles of 

 apatite. Another specimen nearby consists of parallel light-colored 

 bands of quartz and a small amount of orthoclase alternating with 

 somewhat wider dark bands of biotite. In spite of the imposed schis- 

 tosity a fine-grained granitic structure can still be recognized. The 

 quartz and orthoclase are closely associated in interlocking crystals 

 and the few small crystals of plagioclase, a rather acid oligoclase, show 

 but a slight tendency toward automorphism. As is practically always 

 the case in these schists, the quartz has undulatory extinction. Asso- 

 ciated with the biotite is a small amount of muscovite and a few grains 

 of magnetite and titanite. Another specimen taken half a mile south- 

 west of the peak answers well to the above description, but in addition 

 contains small areas of. quartz and orthoclase in micrographic inter- 

 growth. 



