366 University of California Publications in Geology [Vol. 13 



Flat, and in the vicinity of Pawnskin Valley. Thence it branches to 

 the north and south. At the head of Holcomb Creek a large dike 

 intrudes the limestone and the latter is silicified near the contact. A 

 large mass of dark granite extends southwestward from Greenlead 

 Camp beyond Delemar Mountain. It weathers more readily and to 

 smoother forms than the more widespread lighter granite. North of 

 Greenlead Camp the latter swings down to the north slope of the 

 range where it intrudes several other varieties of granite, forming a 

 complex area near the east side of the quadrangle. The Cactus granite 

 is exposed in many places along the north front and at some of the 

 contacts, notable in Furnace Canon, characteristic minerals have been 

 developed. A medium coarse-grained pinkish yellow granite from 

 Arctic Canon was found in thin section to consist principally of equal 

 amounts of quartz and orthoclase with Carlsbad twinning. It also 

 contains a little albite-oligoclase and the principal accessory is a small 

 amount of biotite, some of which has been leached green. Other min- 

 erals present are a few grains of magnetite, titanite, and a few prisms 

 of apatite. A specimen from Blaekbawk Canon was found to be essen- 

 tially the same. It contains equal amounts of orthoclase and quartz, 

 flakes of biotite, and a few crystals of albite-oligoclase ; also a few 

 grains of magnetite and titanite, small flakes of ilmenite, and a few 

 stout prisms of zircon. Both of these rocks are thus practically the 

 same as that described from near Cactus Flat. 



From Granite Peak the granite extends southeastward to the Rose 

 Mine intrusive between the Furnace limestone and Terrace quartzite. 

 Thence it swings to the south and southwest to Big Meadows, beyond 

 which a more heterogeneous mass predominates. In the southwest cor- 

 ner of Round Valley the granite cutting the limestone has been ren- 

 dered gneissie ; but under the microscope it is seen to be practically 

 the same as that farther to the north. In general appearance it is a 

 light yellowish-grey, medium-grained granite containing equal amounts 

 of quartz and orthoclase and biotite as the principal accessory. There 

 are also present numerous small areas of orthoclase and quartz in 

 micrographic intergrowth, and a little oligoclase. A few flakes of 

 muscovite as well as a few grains of magnetite and prisms of apatite 

 are scattered through the rock. Small grains of titanite occur with 

 the biotite and also rounded crystals with high refractive index, prob- 

 ably garnet. The whole section presents a crushed appearance and 

 the quartz exhibits undulatory extinction. A specimen from the north 

 side of the triangular limestone area east of Broom Flat is identically 



