^^g^^ GEOLOGY SAWATCH EANGE. 51 



the bottom, parallel with the river. The surface is covered with huge 

 granite bowlders on both sides of the river ; long, high, rounded ridges of 

 worn bowlders are pileu up as if they had been left by the melting masses of 

 ice. We find the granite rocks in place much worn as we ascend the valley, 

 but no signs of grooving. The coarse texture of the granite permits them 

 to disintegrate readily, and they have a tendency to become rounded by a 

 process which I have termed exfoliation, or a tendency to peel off in thin 

 concentric layers. This is a very common feature in most of the varieties 

 of rock in the West, and the great variety of scenic forms, as well as 

 much of the loose debris or soil in the mountains, is due to this process. 

 Whenever the fires run over the sides of the mountains, burning the 

 forests of pine, the most compact granite rocks scale off in this manner, 

 and undoubtedly the sun's rays, expanding the surface by the heat, 

 produce similar results. Just below the mouth of Pine Creek a high 

 vertical point juts out from the east side of the Arkansas, over the river, 

 of a harder texture and more compact than the contiguous rocks. The 

 jointage, which is nearly vertical, presents strikingly smooth faces and 

 sharp angles. The great variety of texture in the granitic rocks is con- 

 tinually shown, varying from a close fine-grained feldspathic or quartz- 

 itic mass, scarcely affected by atmospheric agents, to a very coarse ag- 

 gregate, readily falling in pieces. Iron in some forms is a very powerful 

 agent also in destroying the cohesion of granites. This hard point seems 

 also to have extended across the river and to have resisted in part its 

 power, so that falls, or rapids, of 25 feet descent have been formed. Just 

 above this point there is a low ridge of granite, which in the wearing 

 out of the valley escaped, while on the east side of the Arkansas there 

 is an old river-bed. These remnants serve to indicate in some degree 

 the nature and extent of the forces that have operated here. They prove 

 that the valley is, for the most part at least, one of erosion. There is a 

 narrow bottom on the west side of the river, with small gulches coming 

 from the hills in which are quite extensive placer-diggings. Small log 

 huts, or miners' cabins, are scattered here and there among the huge 

 granite bowlders, presenting a unique appearance from their diminutive 

 size, compared with the bowlders themselves. 



Perhaps the most interesting and novel features of this region are the 

 great morainal deposits, the remains of ancient glaciers. These proofs 

 of glacial action occur everywhere along both the east and west sides 

 of the great Sawatch or Mother range. But up the valleys of some of 

 the side streams the morainal deposits are more marked and regular 

 than in others. The finest illustration occurs in the valley of Clear 

 Creek, a small stream that flows into the Arkansas Eiver from the 

 Sawatch range, about six or seven mills below Lake Creek. This little 

 stream rises high up near the crest of the range, in a number of exca- 

 vated amphitheaters, and flows for several miles through a close canon 

 until it opens out into the foot-hills on the east side of the range. The 

 valley at once expands to about one-fourth of a mile in width, and at 

 the junction of the creek with the main river has become three-fourths 

 of a mile in width, with a detrital ridge on either side rising 300 to 

 500 feet above the little creek that meanders through it. These 

 detrital ridges show the loose character of the deposits by their 

 rounded forms, being covered over Avith grass and other vegetation. 

 The question would arise, whether the immediate valley of the stream 

 was originally filled up with the glacial detritus, or whether the mater- 

 ials composing these ridges were left on the sides of this branch 

 of the great Arkansas glacier which must at one time have occupied 

 the entire valley. I am inclined to think that the valley through 



