GBANITE AND ARCHiBAN ROCKS. 357 



The granite of Lone Peak resembles this very closely, but shows also 

 a porphyritical structure, carrying large crystals of dull white orthoclase in 

 a crystalline matrix. In this, two principal sets of cleavage-planes, at right 

 angles to each other, are prominently developed, giving the rock a tend- 

 ency to separate into rectangular masses. Lone Peak . itself is a narrow 

 ledge, rising about 1,500 feet above the general surface of the ridge, having 

 ^ on its southern and western side a sheer perpendicular wall as straight as if 

 built of masonry. This wall and the roche-moutonee basin which extends to 

 the southward from Lone Peak are seen in. the colored view of Lone Peak 

 in Volume I. In the narrow^ ravine at the mouth of Big C.ottonwood Canon, 

 where the granite spur of Twin Peak is denuded, a similar porphyritical 

 granite is observed. It is rich in hornblende, biotite, and titanite, and under 

 the miscroscope shows abundant fluid-inclusions, both in feldspars and 

 quartzes, while the larger feldspars present an interesting manner of alter- 

 ation in concentric zones, in the more decomposed of which the fluid-inclu- 

 sions are the less abundant. This granite is in general, however, finer- 

 grained than the temple granite, and in some cases consists merely of quartz, 

 feldspar, and white mica. These latter occurrences are comparatively rare, 

 and associated with the lower mica-schists of the Archsean. 



Along the western flanks of the granite body toward Jordan Val- 

 ley are found some remnants of a series of Archsean quartzites and schists, 

 which have a general strike northeast, and dip from 45° to 60° to the 

 westward. Along the face of the Lone Peak Ridge, these rocks form 

 only a thin shell, covering the ends of the spurs, and are mostly obscured 

 by surface accumulations and soil. In a little ravine, at the contact of the 

 Lone Peak granite with trachyte of the Traverse Mountains, is found a 

 green decomposed rock, consisting largely of hornblende, quartz, and feld- 

 spar, which has been subjected to such great pressure that little of its 

 original structure or composition can now be seen, but which doubtless 

 belongs to this series of rocks. On either side of the mouth of Little Cot- 

 tonwood Caii6n, they consist of a body of quartzites about a thousand feet 

 in thickness, which, on the south side, form a little spur running out from 

 the main wall like a moraine ridge, and, on the north, cover the granite of 

 Twin Peak for a considerable distance up the western slopes, witliout, how- 



