g^^^jjj GEOLOGY ELK MOUNTAINS. 65 



the sedimentary rocks that are visible around the base. There are the 

 black shaly clays which occur above the Dakota group, and whenever 

 they are in contact with the granite core, they are metamorphosed into 

 slates. Debris covered with vegetation conceals the slates below the 

 igneous core for the most part, but on the steep sides a considerable area 

 is exposed here and there, and, so far as we can see, the disturbance has 

 not been great. Just on the opposite side of the stream a bed of blue 

 limestone rises np from beneath the black shales filled with Inoceramus, 

 probably of the age of No. 3. This limestone is partially changed by 

 heat. A little below the Gothic Mountain the stream cuts a gorge 

 through this limestone, with walls 30 to 50 feet on either side, quite 

 compact, and resembling mason-work. The black clays of the Creta- 

 ceous extend up Gothic Peak more than half-way above the bed of 

 the stream, 1,000 feet or more. Near the top of the shales there is a 

 band of trachyte which extends through the peak, along the side of 

 the ridge, to the sources of East Fork, several miles above the peak. It 

 is undoubtedly a dike separated from the main mass of the peak by a 

 band of shales. As it api3ears to one ascending the valley, it seems like 

 a rocky stratum of irregular thickness interstratitied with the black 

 shales. The valley is in part one of erosion. From margin to margin 

 it varies from one to two miles in width. At the upper end the stream 

 separates, one branch extending np into the ridge on the east side, and 

 the other cutting its way through the cross-ridge that separates the 

 East Fork Yalley from the branches of Eock Creek. The west branch 

 cuts through the cros§-ridge of which Bellevue Peak is the prominent 

 point. At the summit of the divide, which is full 800 feet below the 

 summit of the ridge, there is a beautiful green lake fed by the melting 

 of the snows ; and it would be easy to believe that in seasons of higb 

 water the little lake drained both ridges into Eock Creek north, and 

 into East Eiver south. This might be given as a well-marked example 

 of a two-ocean lake if it were situated on the main Eocky Mountain 

 divide. On the cast side of the source of East Eiver are the red beds 

 in their full development, and on the summit the quartzites, yellow, 

 drab, and brown, varying in intensity, depending upon the amount of 

 heat to which they have been subjected. The cross-ridge wliich sepa- 

 rates the drainage of East Eiver from Eock Creek trends about east and 

 west. We i)ass over this ridge and descend into a deep gorge-like 

 valley, with its side-gulches cutting deep through the ridges. This 

 crossridge shows a complete subversal of the sedimentary group from 

 the quartzites to the Cretaceous inclusive. Bellevue Peak is made up 

 of two sets of Cretaceous beds, the upper series being reversed, so that 

 the lowest portioji caps the summit of the peak. This peak is literally 

 riddled with dikes that have changed the shales into slates. This cross- 

 ridge is a part of a long ridge of overturned strata with a trend west to 

 north ten to fifteen miles in length, extending to Snow Mass Mountain. 

 Dikes of trachyte project from the sides of the ridges at different eleva- 

 tions, varying from a few feet to over 100 feet or more, and resembling 

 in the distance massive beds of gray sandstone interstratified with the 

 shales and clays of the sedimentary group. Here and there these dikes 

 are nearly vertical, or incline at a high angle in the side of the ridge. 



From Bellvue Peak we followed a trail on the east side of Eock Creek 

 Gulch, just below the summit of the ridge. The sides and bottom of 

 the valley were composed of the Cretaceous clays with the beds of lime- 

 stone containing characteristic fossils. As we ascend the ridge we find 

 the entire Dakota group overlaid by the Triassic, passing up into red 

 beds, showing most clearly that for ten to fifteen miles the great mass 

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