LARAMIE HILLS. 9 



finer-grained, while at others the change is quite sudden. In some locali- 

 ties, while the rock is still to be classed as a granite, it shows more or less 

 tendency to a gneissic structure, particularly where the mica is abundant. 

 The body of granite which extends to the eastward, and forms an outlying 

 mass to the main range just north of the Chugwater, is more compact in 

 character than the larger mass, although similar in its general features. 

 Just north of the limits of the map, and north of the main stream of the 

 Sybille, is another similar body of compact granite, rough and rugged in topo- 

 graphical character. So far as a somewhat hasty study of these granites 

 in the field indicates, hornblende appears rarely to be a prominent ingre- 

 dient, and only one or two localities were observed where this may be said 

 to be the "case ; one on a small tributary of the North Fork of Crow Creek, 

 and a second on Horse Creek, about two miles above the point where the 

 stream breaks through the Palaeozoic strata. 



The granitoid rocks which form the flanks of the Archaean body of the 

 Laramie Hills present many distinct features in contrast with Mie central 

 granite. They are a compact, massive, and distinctly-bedded series of rock, 

 composed of quartz and feldspar in small crystals, with but little if any mica. 

 In color they are all dark with varying shades of gray and red. The rock 

 is usually tough, breaking into sharp angular fragments, with but little dis- 

 integration, and withstanding atmospheric agencies much better than the 

 central nucleus. These outer granites do not form a clearly-defined con- 

 tinuous body along the entire sides of the range. In some localities they 

 appear to be wanting, and in others they form an intermediate rock between 

 the two characteristic types, with the mineralogical composition of the outer 

 beds, but with a physical habit somewhat resembling the older masses. 

 On the east side of the range, they occur near Lone Tree Creek. They 

 are well developed at Grranite Canon on the line of the railroad, and 

 may be traced to Crow Creek. They are also well shown in the neigh- 

 borhood of Horse Creek. On the west side of the range they may be fol- 

 lowed for a long distance, where they form a low ridge extending north- 

 ward from near the head of Dale Creek, and underlying Sanders Peak. 



At the railroad-cut near Granite Canon, these rocks are well exhibited, 

 and may be taken as typical of the series. They are exceedingly compact, 



