78 SURVEY OF COLORADO AND NEW MEXICO. 



intersected everywhere with basaltic dikes. The first and lowest range 

 runs parallel with it, and is sometimes cut through by it. It seems to 

 be composed of massive feldspathio granite of igneous origin. 



Near the mill, on a little branch just below the mouth of Trout Creek, 

 there is a high rounded peak with a crater-formed depression at the 

 summit which is grassed over, while all around the rim there is a fringe 

 of pines. I am inclined to think it is an old volcano. 



At the point where Chalk Creek emerges from the eruptive range, the 

 sides of the caQon present a singular white chalky apj)earance. This 

 seems to be due to the decomposition of the eruptive rocks, which ap- 

 pear to be true dolerite. 



The drift evidences in this valley are very conspicuous. All along 

 the Arkansas and in the valleys of the little branches are very thick 

 beds of water- worn boulders of all sizes. The last of the eroding forces 

 seems to have come from the range of mountains on the west side. 



The granite on the east side of the river possesses, in a wonderful de- 

 gree, the tendency to disintegrate by exfoliation. There is a kind of 

 bedding which breaks the exfoliation or confines it. In these massive 

 granites there are two sorts of cleavage besides the lines of bedding; one 

 of these is usually vertical and has a strike northeast and southwest, 

 and the other southeast and northwest, inclining twenty to forty degrees. 



On the summit of the mountains is a series of beds, one above the 

 other, of what appears to be basalt, and these beds with the granites 

 beneath them incline each way from Trout Creek Valley northeast and 

 southwest, tOTmiug what apx^ears to be an anticlinal. 



As we ascend Trout Creek Pass, we find granites of all textures from 

 very fine compact feldspathic to a coarse aggregate of crystals. There 

 are also many intrusions of trap. All the rocks seem to weather in 

 the same way, by exfoliation, as if it were the desire of nature to round 

 oif all sharp points or corners. I think it may be said that Trout Creek 

 Valley is a true anticlinal. 



Some time before reaching the top of the pass, we find on the sides of 

 the valley low foot-hills of carboniferous limestone, remnants of a once 

 continuous bed. As we emerge into a little park, just before reaching 

 South Park, we pass through a sort of caiion, with walls of carbon- 

 iferous limestone on each side, inclining northeast at an angle of 

 eighteen to twenty degrees. This limestone rests directly upon the 

 massive granite, and the bedding of the granite inclines in the same di- 

 rection and at the same angle. The limestones are from three hnndred 

 to four hundred feet in thickness. There is one bed, about thirty feet 

 thick, of rusty quartzose sandstone about the middle of the limestone. 

 The lower beds are very hard, bluish, and cherty; but the upper ones 

 are yellow, purer, and contain imperfect fragments of fossils. 



There are here also several examples of the outbursts of basalt, assum- 

 ing very marked castellated forms. 



As we pass into this small park, which is about five or six miles long 

 and two wide, we have on the north side of the road a bed of very thinly 

 laminated black shale, passing up into a great thickness of laminated 

 sandstones, allinclining northeast fifteen degrees, and on the summits of 

 the mountains, four hundred to six hundred feet directly above, are beds 

 of limestone and quartzite inclining in the same direction. The black 

 shales have been prospected for coal. Toward the upper end of this 

 little park is a series of beds, some of them with a reddish tinge, 

 composed of alternate thin beds of shale, sandstone, ijudding-stone, and 

 arenaceous limestones, which belong underneath the black shales before 

 mentioned. 



