74 GEOLOGICAL SURVEY OF THE TERRITORIES. 



the same distance in width. This must have been originally the bed of 

 a glacial lake, scooped out by glacial action as a sort of reservoir for the 

 sediment swept down from the mountain-sides. The sheep-backs com- 

 mence at the lower end of this basin and continue for about ten miles, 

 presenting undoubtedly the most remarkable illustration of this partic- 

 ular kind of glacial action ever seen on this continent. 



The main mass of the peak, like the whole of the Sawatch range, is 

 composed of granite gneiss; The summit of the Holy Cross is covered 

 with fragments of banded gneiss. The amphitheaters on all sides have 

 been gradually excavated, as heretofore described, and the more or less 

 vertical sides show the intermediate steps very clearly. The character- 

 istic feature of the Mount of the Holy Cross is the vertical face, nearly 

 3,000 feet on the side, with a cross of snow which may be seen at a 

 distance of fifty to eighty miles from other mountain-peaks. This is 

 formed by a vertical fissure about 1,500 feet high, with a sort of 

 horizontal step, produced by the breaking down of the side of the 

 mountain, on which the snow is lodged and remains more or less all 

 the year. Late in the summer the cross is very much diminished in size 

 by the melting of the snow which has accumulated in the fissures. A 

 beautiful green lake lies at the base of the peak, almost up to timber- 

 line, which forms a reservoir for the waters from the melting snows of 

 the high peaks. From this, one of the main branches of the Roches 

 Moutonnes Creek flows down the mountain-side, forming several charm- 

 ing cascades on its way. The worn rocks or " sheep-backs" in the valley 

 of the creek display most remarkable examples of the curious markings 

 on the surface of gneiss produced by the separation of the different 

 constituents of the rocks. 



The red feldspar sometimes makes bands or seams crossing each other 

 like mosaic work. Then there are patches of all sizes and shapes, in 

 which the particles of mica are so fine that they appear like rounded 

 masses inclosed in a coarse feldspathic matrix. 



Many of the rocks look as if they were covered with a confused mass 

 of hieroglyphics. These peculiar markings in the structure of gneiss 

 are not uncommon, but they are shown on such a scale in this locality 

 as to attract attention. 



We have already described the canon of Eagle River as monoclinal 

 in part. It runs nearly parallel with the upheaved ridges, but as it 

 descends passes into the sedimentary beds from the granites to the Cre- 

 taceous clays of No. 4. At first the caiion cuts deep into the granites, 

 1,000 to 1,500 feet, with vertical sides; soon the quartzites come in rest- 

 ing on the granites, and then cherty lim^tones of the thickness of 

 1,000 to 1,500 feet, which are undoubtedly a part of the same group seen 

 in the Park range, on the west side of the South Park, and regarded as 

 of Lower Silurian age. The channel cuts through an enormous thickness 

 of variegated beds, not only in color but texture ; a most remarkable 

 group, with an aggregate thickness of 3,000 to 4,000 feet. That this 

 group is of Carboniferous age, the few fossils that could be detected in 

 different localities seemed to testify. 



As we descended this stream toward the main Blue River, the high 

 sloping ridges are seen on the left or south side, the dip well exposed 

 in the channels of the streams that have cut deep down from the 

 mountain-crests. Great quantities of worn bowlders and loose detritus 

 cover these ridges, growing more abundant toward the base or near the 

 river. On the north or right side the outcropping edges of the sand- 

 stones and indurated clays and shales are seen, the texture determining 

 the abruptness of the sides of the canon. 



