FISH CREEK MOUNTAINS. 661 



ranges, even where the older ridges are now buried. If, indeed, such evi- 

 dences were entirely wanting, it would be difficult to understand, unless 

 guided by such upheavals, hoAv volcanic masses like those of the Shoshone, 

 Augusta, and Fish Creek Mountains should form ranges parallel with 

 those of Palaeozoic upheaval, and separated by the same meridional depres- 

 sions which characterize the older formations. The remnants of the older 

 range are represented by granites, followed by uplifted sedimentary quartz- 

 ites, both having a general north and south trend, agreeing with similar 

 exposures in the Augusta Mountains. 



Granite was observed in the Fish Creek Mountains only along the 

 western base, a little northwest of Mount Moses, where it forms the foot- 

 hills and the entrances to the larger canons; seldom, however, having an 

 elevation of more than 300 or 400 feet above the valley. It is very irreg- 

 ular in outline, and, may be traced for several miles either in prominent 

 conical hills or low ridges and saddles, but the exposures would appear not 

 to extend into the mountains for any distance. This granite is a hard red- 

 dish-gray rock, wearing, by atmospheric agencies, into smooth, rounded 

 forms, with all the normal constituents well developed, including dark horn- 

 blende and black plates of biotite. It is a structureless mass, and, so far as 

 our observations were made, would seem to be an intrusive body. 



East of the granite body occurs the quartzite, where it forms a steep, 

 sharp ridge, considerably broken up and displaced by volcanic intrusions. 

 When unaltered, it is a compact gray rock, with a slightly vitreous lustre, 

 but appears to be much decomposed, as if acted upon by solfataric agen- 

 cies. Much of it is characterized by a ferruginous earthy material, which 

 in some places acts as a sort of binding material for loose fragments of the 

 original rock. No direct evidence as to the geological age of this quartzite 

 was obtained ; but as Triassic rocks are the only sedimentary beds exposed 

 in the upheaval of the Augusta mountains to the southward, and as then 

 somewhat resemble quarzite exposures to the westward, they have been 

 referred upon the geological maps to the Triassic age. 



Other isolated exposures of the older rocks may undoubtedly occur, 

 but, so far as examined, the rest of the mountains consist of Tertiary vol- 

 canic material, represented by propylites, rhyolites, and basalts. Of these, 



