458 DESCRIPTIVE GEOLOGY. 



possible to identify, either lithologically or palseontologically, the Ogden 

 Quartzite or the Ute limestone, but the explorations have not been suffi- 

 ciently exhaustive to justify the conclusion that they are entirely wanting. 



The east face of the Bonneville Peak Hidge presents an almost perpen- 

 dicular wall of qUartzite from 2,000 to 3,000 feet in height. The deep canon 

 under this peak at the head of South WilloW Creek has the amphitheatre- 

 like basin at its head, aiid the general shape in its upper part, of a glacier- 

 cafion. This cation was only explored in its lower portion, where a heavy 

 body of blue limestone, covered at the foot-hills by a flow of trachyte, is 

 exposed in section, with a strike a little West of north. These limestones 

 are much metamorphosed aiid dislocated, standing at such varying angles 

 that it was difficult to determine their structure. But few imperfect casts 

 of fossils were obtained from the loWer beds exposed, among which the 

 only one which has been specifically recognized is ZapJirentis muUilamella. 

 Their general chai'acter*, however, and the thickness and general habit of 

 the limestones are sufficient to determine them as belonging to the Walisatch 

 group. 



Near the mouth of the caflon, a body of trachyte is exposed, which 

 has appal-ently poured out between the nearly upright beds of limestone, 

 while flows of Volcanic ash of red atid gray color, containing pebbles 

 and angular fragments of the lava, form the ridges on either side of the 

 entrance, sloping 20° to the east, and apparently covering the flanks of the 

 spurs to a considerable distance north and south. This rock is a light-gray 

 hornblende-trachyte, cotitaining abundant fine black needle-like crystals of 

 hornblende, with some black biotite, but no distinct crystals of feldspar. 

 The mass is quite porous and rough to the touch, and has a low specific 

 gravity. Under the microscope, the grayish-white porous groundmass is 

 found to be made up largely of feldspar crystals, in which plagioclases are 

 comparatively frequent, with abundant biotite in remarkably perfect hexa- 

 gons and rhombs, while no microscopical hornblende Was seen. The ground- 

 mass contains besides some apatite, and fine globulitic glass stains, which, on 

 account of the colorless zone encircling them, might be mistaken for nosean. 



The limestone beds in the upper part of the canon have apparently a 



