Rocky Mountains. 407 



within a short distance of each other, would probably receive 

 from mineralogists the different appellations of primitive, 

 trap, hornblt-nd rock, greenstone, sitnite, &c. But, as the 

 rock graduates by imperceptible degrees from one of these 

 into all the rest, it probably may be found in the same way, 

 passing into granite. It often contains quartz, but little or 

 no mica. From the Platte southward to the High Peak, the 

 mountains are entirely of a granite, in which the predomina- 

 ting ingredif nt is feldspar. This feldspar is usually flesh 

 coloured, and sometimes reddish brown. Its crystalline form 

 is often distinctly seen in masses, where small fragments of 

 mica and quartz are intermixed. The fragments of quartz 

 are small, and minutely blended with the other ingredients. 

 The mica is usually black, and in small scales; it is also m 

 small proportion, compared with the quartz and hornblend. 

 At the foot of the High Peak, the lower region of the moun- 

 tain IS strewed with many small masses of rocks, among 

 which may be found well marked specimens of gneiss, and a 

 few of mica slate. The former of these rocks is found in 

 place about ten miles to the west of the Peak, at the place 

 where the Arkansa leaves the mountains; but we have no 

 where seen mica slate, except in small detached masses. The 

 granite, which forms the base of the Peak, is similar to that 

 already described. By the action of atmospheric agents, it 

 crumbles rapidly into small fragments of the size of a nut. 

 The steepest parts of the side of the mountain are every 

 where covered with these small and loose masses. No con- 

 siderable change occurs in the geological character of the 

 mountain, until you arrive at the base of the last cone of the 

 Peak. Above this point no mica is found; the rock, like that 

 of the summit of the Silla of Caraccas,* the cataracts of 

 Atures, and many high points in the mountains of South 

 America and Mexico, and like that of Syene in Egypt, is a 

 granite, consisting of quartz, hornblend and feldspar, but so 

 minutely divided, and so closely aggregated, as to appear 

 like a homogeneous mineral- It is extremely compact and 

 hard, and seems to bid defiance to every agent that would 



nite of Lake Cbamplain, rising into the high mountains of Scroon, and of 

 the tract about the sources of the Hudson, known as " Totten Crossfields 

 patent," and which have been pronounced sienite, he will be convinced 

 that whatever those rocks may be called, they ought to be considered as 

 intimately connected with the granite, and as having had a similar and 

 <iimultaDeous origin. 



* Humb. Per?. Nar. vol. iii, p. 405, and vol. v, p. 19. 



