holmes.] FAULT FOLD OF THE ELK EANGE. 69 



strata, and at Aspen Creek, as previously mentioned, only the Upper 

 Cretaceous remains in view, with a fragment of primordial rock 

 at a in the deepest part of the valley. South of Aspen Creek for 

 a few miles the whole series seems to be depressed beneath the sur- 

 face, while the granite peaks on the east side of the fault-line rise 

 to' the height of 3,000 feet, making a total displacement of at least 

 11,000 feet. South of b there is a high, sharp ridge formed of a series of 

 almost vertical Carboniferous rocks, which seem to have been carried 

 up by the granite, or at least to have been left in the present position 

 by the dragging of the fault. In the south end of this ridge the dip 

 increases from 90 to 135 degrees, that is, 45 degrees beyond the vertical, 

 and nearly the whole series of sedimentary rocks appear in this position 

 in the side of the canon at c. 



In the triangular spur between c and d, a large mass has been carried 

 back 90 degrees past the vertical, so that the Silurian quartzites oc- 

 cupy the top of the ridge, and the Cretaceous rocks the bottom of the 

 valley. 



The fold has been so sharp at e that the beds have been broken off, 

 and the continued upward movement of the granite has bent the broken 

 edges up, producing a synclinal in the inverted strata. 



In this place the belt of granite is quite narrow, so that the relative 

 positions of the strata on opposite sides can be studied with ease. 



The Silurian rocks of the east side outcrop on the summit of the 

 water-shed of the range at f 2,000 feet above the creek, and since the 

 Middle Cretaceous rocks of the west side are depressed to an unknown 

 depth beneath the creek-bed, we can safely say that there is a vertical 

 displacement of at least 8,000 feet. 



The amount of lateral movement (at right angles to the axis of the 

 fault) may be expressed by the difference between the width of the gran- 

 ite belt e/and that of the inverted fragment d e, and will hardly fall 

 short of 6,000 feet. 



South of e the beds gradually rise again from the inverted position, 

 and a high, narrow ridge is formed of the almost vertical Carboniferous 

 rocks. This ridge is not above four miles in length, and is connected 

 with the main range by an irregular eross-ridge that separates the head- 

 waters of the north and south branches of Rock Creek. The tongue of 

 granite that extends southward from Snow Mass along the fault-line is 

 obscured before reaching this cross-ridge by the overlapping sedimen- 

 tary rocks (at h). Here the greatest confusion occurs, and large masses 

 of the rocks, of all ages, are found in the most unheard-of relations to 

 each other. The strata of the west side have been depressed and caught 

 beneath the encroaching strata of the east side, and are folded back 

 upon themselves, as seen in the drawing, Figure 11. This peculiar and 

 somewhat irregular fold may be traced for a distance of six or seven 

 miles, and in this distance is cut at right angles by three immense val- 

 leys. The sections exposed in the faces of these are not always distinct, 

 but at the same time make it possible to study the peculiar anatomy of 

 the fold. I observe that in every place where there is an exposure the 

 Carboniferous rocks of the east side rest upon the upper surfaces of the 

 bard sandstones of the Dakota group, and with such a degree of regu- 

 larity that I was for a long time in doubt as to the identity of the latter. 

 In studying the section exposed on the north side of the valley which 

 crosses the fault at i, I began near the crest of the main range west of 

 Maroon Mountain, and passed down through nearly 3,000 feet of Carbon- 

 iferous sandstones, limestones, and conglomerates (which have a gen- 

 tle dip to the east and undoubtedly belong to the eastern side of the 



