HAYUEx.] GEOLOGY FROM ELK MOUNTAINS TO MIDDLE PARK. 71 



with partings of shale. The layers of limestone vary from 4 inclies to 

 4 feet in thickness. As we ascend the sandstone predominates, and 

 becomes coarser until layers of rotten coarse sandstone alternate with 

 beds of pudding-stone and conglomerates. Some of the sandstones are 

 quite coarse in texture, and might be called pudding-stones. Indeed, the 

 whole section is a repetition of the one near Horseshoe Mountain. 



The stratified beds are here over 1,000 feet in thickness above the 

 bed of Eagle Eiver. It would seem, therefore, that we have here on the 

 west slope a series of quartzites and impure limestone, like those resting 

 on the granites in the Park range, and most probably of the age of the 

 Lower Silurian ; above them a thick group of Carboniferous beds with num- 

 erous fossils, as Spirifer, Prodtictus, and a trilobite, probably a Phillysia. 

 These fossils are found quite abundantly as soon as the more modern 

 beds occur. To the eye of the field-geologist this lower group of beds 

 presents a much more ancient aspect, where it is seen, than the Carbon- 

 iferous, although there are no remarkable instances of inconform ability 

 that have come to my notice. I think I can always detect the line of 

 deraarkation between the older group and the Carboniferous series in 

 all cases without the aid of fossils or other proofs, merely by the differ- 

 ence in the general external appearance. As we pass lower down the 

 valley of Eagle Eiver, we. find high bluff- walls on both sides of the 

 river, with several hundred feet of rather loose arenaceous beds with 

 hard layers of sandstone and quartzite alternating, of yellow and brown 

 color, evidently extending the Carboniferous group 800 to 1,000 feet 

 above the reddish-brown sandstone. This upper group of beds rises to 

 the summit of the ridges as we ascend the river, and probably forms the 

 ux)per portion of the Carboniferous series. The color of the rocks in this 

 region cannot be depended upon as of any value in tracing groups of 

 strata over large areas. 



The same white quartzites which we have mentioned above as resting 

 upon the gneiss a little farther below hold the same position, but 

 are quite red. They may be white, gray, red, rusty-yellow, or brown, 

 within comparatively short distances. 



In the canon of Eagle Eiver the order of superposition is well shown. 

 The canon is undoubtedly one of erosion for the most part, though, like 

 that of the Arkansas Eiver, it is also monoclinal. At the present time 

 the indications of any original fracture or fissures are only suspected 

 by the inclination of the stratified beds on either side of the river. The 

 dip is to the east and northeast from the gTeat Sa watch range, of which 

 the Mountain of the Holy Cross is the northern end. The erosion lias 

 been so great that the sides of the caiBon for miles are nearly vertical, 

 although the left or east side is much more abrupt. 



Sometimes the quartzites that rest on gneiss will wall in the valley 

 at the river's margin ; again they will cap the summit of the ridges 

 1,000 feet or more above the bed of the river. 



Both sides are penetrated with dikes to a greater or less extent. At 

 one locality, above the Silurian limestone, is abed of trachyte, apparently 

 interstratified, with a bluff-front of 50 feet, with marked vertical and 

 horizontal jointing. So far as 1 could discover, it does not extend 

 horizontally more than 100 yards. Sometimes the igneous material 

 rises up through vertical fissures without much disturbance of the con- 

 tiguous beds, and again it throws it into chaos, so that while the gen- 

 eral or aggregate inclination is north or northeast, the local dip is liable 

 to be in any direction or at any angle, depending upon the force exerted 

 by the igneous outflow. As we strike the main branches of Eagle 

 Eiver and they unite, the main river flexes slightly toward the west, 



