62 GEOLOGICAL SURVEY OF THE TEREITORIES. 



has evidently been cut through these quartzites. The same rocks under- 

 lie the mountains on the opposite side of the river, and resting unconfor- 

 mably on the quartzites are at least 1,000 feet of Carboniferous limestone, 

 exceedingly cherty, impure, of a yellowish-gray and brown color, and so 

 massive that the stratification is quite indistinct. These limestones possess 

 a great variety of textures. Above them are a series of beds, standing in 

 nearly a vertical position', alternating with clays which have been worn 

 away by atmospheric forces, so that the harder layers project above the 

 surface in jagged edges. The harder layers are mostly yellowish cherty 

 limestones. The band of indurated brick-red clay is 50 to 100 feet thick, 

 and from its bright scarlet hue attracts the attention of travelers from 

 all points of the compass. A bed of yellowish-gray quartzite forms one 

 of the walls of the Devil's Slide*and is probably near the summit of the 

 Carboniferous group in this locality. The excellent illustration, (Fig. 

 11,) taken on the spot by Mr. Elliott, shows the nearly vertical wall of 

 quartzite on the right, the broad interval covered with debris, grass, 

 and a few scattered pines ; and on the left, the huge wall or dike of ba- 

 salti The low interval is composed of dark steel-gray slate, extends 

 from the summit to the base of "the hill, and is about 150 feet wide. The 

 south wall or dike is very -compact trachyte, stands nearly vertical, 50 

 feet thick, and at some points 200 feet high. It is probable that this 

 igneous mass was thrust up between the strata, since they were ele- 

 vated to their present position, and doubtless during the Pliocene pe- 

 riod. On either side of the dike, the clays have been changed into 

 the metamorphic slates. Fragments of the slate are attached to the 

 walls high up on either side. This is a remarkable feature in the geol- 

 ogy of this region. Far to the left or south of the dike the jagged ver- 

 tical edges of the Jurassic strata can be seen. The inclination of all 

 these beds ranges from 60° to 80° southwest. The two walls of the 

 Devil's Slide stand at an angle of 80°. The interval near the sum- 

 mit of the hill is rather narrow, but expands out at the base to dou- 

 ble the width. Above this dike, in order of superijosition, though 

 now standing side by side, is a grou]3 of Jurassic strata — first, a low 

 interval of shaly, marly clay, ashen brown; secondly, brownish-gray 

 arenaceous limestone, with Iragments of fossils that are evidently 

 Jurassic, 50 feet thick; dip, 70°; thirdly, purplish and reddish indu- 

 rated, slaty clay, with seams of sandstone projecting but little above 

 the surface ; fourthly, a bed of trap 6 feet' thick ; fifthly, slaty clay 

 sandstones, the upper part a fine pudding-stone, standing nearly vertical, 

 70° to 80°, 100 feet; sixthly, numerous layers, which may be aggregated 

 as alternate beds of yellowish-gray quartzites and slaty clays, varying 

 but little in texture, the harder portions standing up in more or less 

 jagged edges, with the softer clays washed out from between them ; dip, 

 60° to 70; 300 feet; seventhly, 200 feet of ashen-gray shales and sand- 

 stones ; eighthly, 400 to 600 feet of alternate beds of shaly clay sand- 

 stone and quartzites. This last group doubtless contains the Lower 

 Cretaceous beds. The harder layers, 6 to 10 feet thick, rise above the 

 general surface of the mountain-side like walls. The dip is 50° to 60°. 

 The dark laminated clays of the Cretaceous passing up into the Upper 

 Cretaceous are well shown with jjerfect continuity, then passing up into 

 a great thickness of somber brown sandstones of the Coal group. There 

 is a great uniformity in the Upper Cretaceous and Tertiary series. We 

 can detect some variations in color and texture, but they are of minor 

 importance, and could not be easily described in words. At one point 

 the strata are much crushed together. The dip of the beds just described 

 is toward the southeast ; but, by the elevation of the mountain to the 



