LARAMIE HILLS. H 



The low percentage in lime is quite remarkable. It would indicate that 

 the triclinic feldspars cannot be either anorthite or labradorite. By the 

 detection under the microscope of apatite in most of the Archaean rocks, 

 and the presence of phosphoric acid in the specimens chemically examined, 

 it would seem conclusive that at least a portion of the lime is present in 

 the form of phosphate of lime. 



Near the upper streams of the Chugwater, the granites gradually 

 assume a laminated appearance, and pass into well-defined gneiss and 

 schist. The minerals arrange themselves in thin parallel bands, or layers, 

 which, however, are constantly subjected to alteration. In many places, 

 this parallelism is best observed by studying the rock-formations at a dis- 

 tance. On the north side of the. upper branch of the Sybille Creek, large 

 heavily-bedded masses of a dark hornblende-gneiss form the canon-walls. 

 It is a fine-grained rock of quartz and light-colored feldspars, with fibrous 

 hornblende as the predominant constituent. This rock forms a distinct 

 feature of the gneissic beds of the north end of the Laramie Hills. To the 

 south of the central granite body, as already mentioned, gneissic formations 

 occur, and east of Signal Peak identical hornblende-gneisses make their 

 appearance, and give the character to the east- side of the range in the region 

 of Lone Tree and Box Elder Creeks ; they have a decided dip to the east, 

 and nearly a north and south trend. The prevailing rock, however, is a 

 pearl-gray gneiss with the minerals arranged in irregular, parallel zones, 

 -which pass imperceptibly into a granitoid rock, but always retaining more 

 or less of the stratified arrangement of the minerals. These granitoid 

 masses appear to be interstratified between layers of gneiss. 



A specimen from Signal Peak is a typical rock from this region. A 

 compact, fine-grained, fresh-looking mass of gray quartz and light-colored 

 orthoclase- and plagioclase-feldspars, with the mica mostly in very fine lami- 

 nae, in knots and bunches. Under the microscope, minute zircons have 

 been detected, and a chlorite-like mineral, which appears to replace the 

 mica. Very similar rocks form the broad table between Dale and Dead- 

 man's Creeks, with the mica, however, somewhat more abundant. All these 

 gneissic rocks present, in general, great uniformity of lithological structure; 



