32 SURVEY OF COLORADO AND NEW MEXICO. 



stones, limestones, &c., have a tenclenc}^ to weather by this process of 

 exfoliation, and the hills and monntain-peaks follow the same rnle. It 

 wonld seem that nature abhors sharp angles and corners, and com- 

 mences at once to smooth and round them off, so that nearly all peaks 

 and hills have this rounded appearance when closely examined. The 

 huge masses of granite or basalt on the summits of the highest moun- 

 tains are now undergoing this process of exfoliation. 



The lirst bed of granite that lies west of the high ridge of sandstone 

 inclines 5S°, and has much the appearance of sandstone completely met- 

 amorphosed. It is of various degrees of fineness, but mostly an aggre- 

 gate of coarse crystals of feldspar and quartz. There is also a bed of 

 mica schist incliuing with it at an angle of 48°. I have made use of 

 these gneissic beds to aid me in forming a clearer idea of the true strat- 

 ification or bedding of the granite, which is often obscure. 



The massive beds of sandstone which form the high walls are evi- 

 dently partially metamorphosed by heat. The bottom beds, which lie 

 next to the granites, are composed of a rather coarse aggregate of 

 crystals of feldspar and quartz, inclosing multitudes of well water- 

 worn pebbles of all kinds, from a minute size to several inches in diam- 

 eteV. There are also fragments of unchanged reddish sandstone, but 

 the inclosed pebbles are mostly metamorphic, among which quartz peb- 

 bles are conspicuous. 



The inclination of the first ridge is about 33°. A portion of it is so 

 fine and compact that it has somewhat the appearance of imperfect jas- 

 per. It varies much in texture. A most interestiug feature is the sep- 

 aration of this inner ridge from the one just east of it. It has evidently 

 been broken off from the summit of the next one east of it, and the 

 whole mass carried forward westward, yet retainiug nearly the same 

 angle of inclination. This is shown by the fact that the granite rocks 

 are thrust up under and between the ridges, showing most distinctly 

 that this is an immense fragment of the second ridge from the inside, 

 elevated upon the edges of the granitic rocks and carried two hundred 

 or three hundred feet to the westward. Yet the agency that performed 

 this movement acted so quietly that it did not disturb its position in rela- 

 tion to the other ridges. 



The second or main ridge from the inside varies in dip from 30° to 

 45°. It is largely composed of pudding-stone or fine conglomerate, with 

 layers of sandstone of various degrees of fineness. The upper beds 

 are composed of fine-grained sandstone. The entire ridge must have 

 had a thickness of eight hundred to twelve hundred feet. 



The scenery along the flanks of the mountains at this point is won- 

 derfully unique, and I have never known a similar example in the 

 Kocky Mountain region. The uplift is on an unparalleled scale. 



Toward the outside, or, more properly, the upper layers of this ridge 

 become close-grained, much of it breaking into cubical blocks and 

 forming a great accumulation of debris on the sides of the mountains. 

 The outermost layer of this ridge, which has been Avorn off so as to be 

 a low one, inclines 54°. All the beds exhibit less and less the influence 

 of heat from the inner to the outer side, and much of the upiDcr i)art is 

 a compact, close-grained quartzose sandstone, divided into layers with 

 smooth surfaces, and most excellent for building purposes. 



The next bed is a loose red sand, so soft that the upturned edges 

 have been worn down and completely grassed over. The upper edges 

 of this bed are at least twelve hundred feet below the summit of the 

 high sandstone ridge. The dip is 31°. At the foot of the slope of these 

 red beds is a grassy valley, and then a very abrupt ascent to the edges 



