SUEVEY OF COLORADO AND NEW MEXICO. 31 



higli angle, about 45°, and are not easily worked. The sandstones pro- 

 ject up above the loose material like irregular walls, and the creek itself 

 forms a narrow passage or gorge through one of these ridges. 



Between the sandstones, and apparently with very little clay either 

 above or below, is one bed of coal four to six feet thick, which was 

 wrought for a time, and then abandoned. 



It seems to me the coal here will never be worked with profit. Above 

 the sandstone there is another bed of coal, and above that, fire-clay ; all 

 the strata conforming and inclining between 35° and 45°. The sand- 

 stone ridge on the north side of Coal Creek becomes more nearly verti- 

 cal — 68°. All the beds of coal are so badly crushed together that they 

 are rendered somewhat obscure. There are here two or three feet of 

 clay between the layers of coal, and above the coal the clay is very irreg- 

 ular; sometimes thinning oat entirely, so that the sandstone comes 

 directly upon it. A large number of the sandstone ridges may be seen 

 far out in the plains, east of the mountains, at intervals, all having the 

 same general trend, and inclining at various angles. They rise above 

 the grassy plains in isolated piles, like broken-down walls. These sand- 

 stones indicate the existence of coal beneath, but it would be utterly 

 impossible to work out the sequence of these beds only at the most 

 favorable exposures. In almost all cases the tertiary beds are so worn 

 down and covered with superficial deposits that they are detected only 

 in the channels of streams, or by the sandstones projecting above the 

 grassy surface of the plains. 



July 6. — With Mr. Marshall as guide, I attempted to penetrate through 

 the sandstone beds to the metamorphic rocks up Bear Canon, a sort 

 of separation in the immense sandstone wall between the two Boulder 

 Creeks. So far as I could ascertain in this caiiou, the sedimentary beds 

 lie fairly against the metamorphic rocks, and the latter incline in precisely 

 the same direction, and at about the same angle as the former, a little 

 north of east. There is another point that seems to me to be well shown 

 in the range; and that is, that the metamorphic rocks are thrown up in 

 distinct auticlinals, the same as the sedimentary beds. As soon as we 

 pass the junction of the unchanged and changed rocks we find the granites 

 inclining in the same direction, and a little furtlier up there is a ridge 

 inclining in the opposite direction, forming in the interval a valley. 

 The angle of dip on the west side of the granitic anticlinal is 44°, a little 

 south of west. This anticlinal feature may be local here, but I regard 

 it as a common occurrence in the metamorphic rocks of the mountain 

 ranges. 



Here tremendous uplifts of the sandstones ax)pear about 4,000 feet 

 above the Boulder Valley in the plains below, and their rugged summits 

 l^roject far over on the granitic rocks westward, so that along the little 

 stream immense masses have fallen down from the broken edges, a half 

 a mile above the junction of the two kinds of rocks. I think this illus- 

 tration alone furnishes sufiicient evidence that the sedimentary beds once 

 continued uninterruptedly across the area now occupied by the mountain 

 ranges, and that these beds only form a part of what was once a gigantic 

 anticlinal, the eastern portion of the unchanged beds remaining, while 

 the western portion has been worn away and mingled with the debris 

 of the plains. Further up toward the central axis of the mountain we 

 pass ridge after ridge of granite, inclining eastward about 36°. 



The process of disintegration of the rocks by extbliation is here shown 

 quite clearly, without regard to stratification. Immense masses of rock 

 are weathered into rounded forms by these coatings or layers falling off. 

 I have observed that all kinds of rocks, granites, igneous rocks, sand- 



