622 - DESCRIPTIVE GEOLOGY. 



forms of liornblende and mica. In addition to the above, the microscope 

 reveals the presence of titanite and apatite. These three rocks, the granite, 

 diorite, and dacite, form actual outcrops through the quartzite. The granite 

 is evidently earlier than the quartzite, since the beds rest their upturned 

 edges against the granitic flanks, while the diorite and dacite have broken 

 through the quartzites subsequently to their upheo.val. 



In general, the quartzites have a southerly and easterly dip, chiefly 

 easterly; but between the granite and dacite there is what appears to be a 

 local and limited fold, producing a westerly dip. In general, the entire mass 

 may be considered as one member, having an easterly dip. The uppermost 

 layers of the quartzite are very compact and dark, and bedded in thin sheets, 

 passing into fine, fissile, and argillaceous slates, both of which pass upward 

 through a gradual transition into beds of fine argillaceous limestone. Diligent 

 search was made in these latter beds for fossils, but to no purpose. There 

 occur curiously flattened lenticular concretions, which may possibly represent 

 some remains of animal life, but no distinct forms could be recognized. 

 These limestones are very slightly developed, nowhere exceeding two hun- 

 dred feet in thickness. They have been supposed to represent the lower 

 members of the Ujiper Coal-Measure limestone. They are best developed 

 on the heights south of Shoshone Peak at the head of Trout Canon. Pass- 

 ing down Trout Canon, an immense thickness of quartzites is seen, all con- 

 formable and dipping to the east, and varying from thick heavy gray beds 

 to thin black fine-grained flinty quartzites, having a peculiar sulphur-yellow 

 stain. There is a strong tendency in these fine beds to shrink up, leaving 

 irregular open cracks along the planes of deposition. 



Upon the outcrops of the siliceous schists on the ridges south of Sho- 

 shone Peak, wherever the rock -masses are prominently exposed to the air 

 and sun, they become coated with a film of black metallic oxides, iron and 

 manganese, but chiefly iron, which is as brilliant as a graphitic polish. It 

 closely resembles certain basalts observed in Arizona. It was especially 

 noticeable that the polish was less on the north side of the outcrops thati 

 on the south. This may be due in part to the abrading force of the snow 

 and ice particles driven by the north winds of winter. • Otherwise it would 

 seem that the effect was purely a solar one, and it is difficult to understand 



