40 8 JOSEPH H. PERRY 



red to a dark gray. The gray is the prevailing color, while red 

 is more characteristic of the porphyry nearer the granite. The 

 porphyry is massive and without foliation, and is cut by many 

 joints into quite small, irregular, sharplv angular blocks. 



The quartz is very noticeable. It is smoky in hue, and 

 occurs generally in distinct rounded anhedra one-sixteenth to 

 one-eighth inch through. Now and then among these anhedra 

 may be found a bipyramidal quartz crystal. On the east slope 

 of the mountain, at about the 2,000 foot level, was found a gray 

 quartz-porphyry abounding in quartz crystals, so that every 

 broken surface and every weathered surface presented many of 

 the little projecting pyramids, and the six-sided tapering cavi- 

 ties from which crystals had been broken. The porphyry abound- 

 ing in quartz crystals is at a considerable distance from the 

 granite beneath. 



In the porphyritic phases having the finer-grained ground- 

 mass there are orthoclase phenocrysts, but in the coarser-grained 

 varieties the intercrystallizing feldspars constitute the ground- 

 mass about the quartz particles with only a trace of the finely 

 grained mixture. 



-Different specimens of the porphyry afforded on analysis the 

 following results : ^ 



'Other determinations were not made. Methods given in Bulletins 148 and 176, 

 U. S. Geo/. Sufv., were carefully followed. 



