346 University of California Publications in Geology [Vol. 13 



biotite. Still higher it resembles that at the bottom, except that it is 

 much coarser. Above this biotite rock is a fine-grained quartzite con- 

 taining small flakes of muscovite, but showing no bedding. 



The schists two miles farther up the canon are highly altered and 

 it seems likely that some were originally igneous. On the west side 

 the schistosity strikes N 30° E and dips 30° SE and the lower portion 

 is largely black schist. Under the microscope it is seen to have a very 

 fine texture and to consist of quartz with enough green hornblende 

 to give the rock its dark color. A small amount of biotite is arranged 

 in streaks with the hornblende. The rock also contains numerous 

 small grains of titanite and a few small prisms of apatite. No feld- 

 spar could be seen. Above this there is a dark schist consisting largely 

 of brown biotite, some muscovite and hornblende, and lenticular pheno- 

 crysts of orthoclase with carlsbad twinning, some of which are more 

 than three centimeters across. Under the microscope these large crys- 

 tals are seen to have irregular boundaries due to the other minerals 

 jutting into them and flakes of muscovite are scattered through them. 

 The ground mass contains considerable quartz and an altered feldspar, 

 probably orthoclase, including a few needles of apatite. Numerous 

 grains of titanite and a small amount of magnetite are also present. 

 The rock is probably of igneous origin and it may have been intruded 

 into that described above, but the schistosity imposed upon both of 

 them has obliterated any positive evidence of such relationship. They 

 have been cut by pegmatite dikes which still exhibit their character- 

 istic graphic structure in spite of being much decomposed. Epidoti- 

 zation is common in the black schist and apparently progresses along 

 fissures from which it extends out into the mass. 



Nearly all the rocks on the ridge between Aker's Camp and Oak 

 Glen are schistose. They strike approximately parallel to the ridge 

 and dip 50° to 80° to the north and have been so metamorphosed that 

 it is difficult in many cases to tell whether they are of sedimentary or 

 igneous origin. That north of Oak Glen looks like a medium-grained 

 gneissic granite and consists of quartz, biotite, and a feldspar. Much 

 of the biotite has been chloritized. Near the crest of the ridge south- 

 west of Aker's Camp a thin lens of marble was found which suggests 

 sedimentation, although there still remains the possibility of calcite 

 having been deposited in a fissure before schistosity was impressed 

 upon the adjacent rocks. 



The granites east of Mountain Home Creek show great diversity 

 in both composition and texture. In several places there are darker 

 rocks, high in biotite, having the appearance of inclusions and rang- 



