RAVENSWOOD PEAK. 637 



tance of 8 to 10 miles south of Eavenswood Peak, where it has a due north 

 and south trend. This granite has remarkably regular bedding planes, 

 apparently conformable to those of the overlying slates, which give it the 

 appearance of being a stratified granite, though at the same time it traverses 

 the. slates in dikes. It is a white, fine-grained rock, made up of feldspar, 

 quartz, and white mica, and containing neither hornblende nor titanite. 

 The feldspars are mostly orthoclase, though there seems to be some little 

 admixture of plagiocfese. Under the microscope, the quartz -crystals are 

 seen to be remarkably poor in fluid-inclusions, and the rock contains a little 

 apatite, but no biotite whatsoever. In a dike which traverses the slates 

 near the summit of the ridge, the rock is much coarser-grained, but shows 

 the same constituents. , 



The slates have a north and south strike, and dip away from the granite 

 body at an angle of about 45° to the west, and to the eastward at a still 

 higher angle, but are mostly obscuVed on this side by the rhyolite flows. 

 They are fine-grained micaceous slates, very fissile, and having a glistening, 

 nodular surface. Among these slates is a peculiar dark-purple, fine-grained 

 rock, which is found largely developed in the Montezuma Range near 

 Trjpity Peak and in the Pah-tson Mountains. In a hand-specimen, it is so 

 fine-grained that it might almost be taken for an anamesite. Under the 

 microscope, however, it is seen to be made up of a fine crystalline mixture 

 of quartz, and brown and white mica, with particles of black magnetite and 

 some few grains of hornblende. The connection between this Archaean 

 body and the other sedimentary bodies is obscured by the intervening flows 

 of rhyolite. 



In geological structure, the Ravenswood Peak mass is extremely com- 

 plicated. It consists of a body of granite and porphyry, which has broken 

 through an uplift of quartzites and limestones, all of which have been cov- 

 ered by an extensive flow of diorite, now forming the summit of the peak, 

 and extending out for a considerable distance to the east and west. The 

 granite is obscurely exposed in the caiion on the south side of the peak. It 

 is essentially different from the Archaean granite, and evidently of later 

 origin. It consists of milky orthoclase, with a little triclinic feldspar, large 

 quartz-grains, which are pellucid and cracked like those of rhyolite, with a 



