64 GEOLOGICAL SURVEY OF THE TERRITORIES. 



fied rocks inclining at small angles. Again, the beds are tipped off 

 from the granite core at all angles from 10° to a vertical, and not unfre- 

 quently past a vertical, and there are in the Elk range the most won- 

 derful instances of the complete overturning of immense groups of beds, 

 so that for several miles there is a double series, from the Silurian up to 

 the Cretaceous, inclusive, and then rising upward in inverse order, as is 

 shown at the head of East Eiver and near Snow Mass Peak. 



Again, the two forces, one vertical and the other tangential, seem to 

 have acted at the same time, throwing 1,000 feet or more of older 

 strata directly over rocks of more recent age. The complications are 

 so great in the Elk Mountains that we could only make a preliminary 

 survey, and a special study must be made of this entire range. This 

 we propose to do the coming season. 



By looking at the map of Elk Mountains it will be seen that several 

 streams have their sources in the Whiterock Peak. The little branch 

 that rises at the north side and flows around to the southward has 

 already excavated its amphitheater back nearly a mile, while the granite 

 here is rounded or smoothed as if by the movements of masses of ice, 

 though much of the erosion must have been performed by the movements 

 of vast masses of loose earth and debris. From the real base of the 

 mountain one can follow up this gulch for several miles, rising, as it 

 were, step by step, on a series of irregular terraces, which are the result 

 of these accumulations of debris. In this instance, the difference of 

 elevation of the real base of the peak and the immediate foot of the 

 crest is at least 2,000 feet, and the width from a fourth to a half a mile, 

 so that one can arrive at a moderate estimate of the tremendous work of 

 erosion which has been performed here. At the head of this amphitheater 

 the crest is so narrow that it was with extreme difficulty that we could 

 creep along it, and we could look down on every side into similar exca- 

 vations. These mountain-ranges, of which the high peaks now form 

 the conspicuous features, were originally of considerable width, varying 

 from half a mile to several miles, but now the crest or divide may be 

 represented on the map as a zigzag line ; the sources of the little streams 

 running not unfrequeutly from them, having already removed this crest 

 for a little distance, thus forming a kind of low pass. The sides or 

 walls of these gulches are usually very steep, in many cases vertical, 

 but when the upper portions are composed of the easily (disintegrating 

 sandstone, the vegetation, of a most vivid green color, has crept high up 

 on the sides, and the upper border is composed of a series of tongue-like 

 points, which give to the picture a unique appearancQ. It would appear 

 as if the grass had struggled ineffectually to scale the sides of the gulch 

 to the very crest. In some instances these little tongues or points do 

 extend 20 to 50 feet above the main mass below. The melting of the 

 snow forms little furrows down the steep sides, and between them are 

 the sharp points or tongues of vivid green vegetation. 



Ascending the valley of East Creek near its source, we pass over the 

 sands and clays of the Cretaceous group, containing a few characteristic 

 fossils, as the Baculites ovatus, and several species of Inoceramus. As 

 we proceed west and northwest the Cretaceous rocks increase in thick- 

 ness and extent. The valley of the East Fork, as we see it near Gothic 

 Peak, is a kind of monoclinal, the rocks apparently inclining in the 

 same direction, the west side being abrupt, while the east side has a 

 steep slope. Gbthic Mountain is composed of a vast mass of igneous 

 granite projected up through the superincumbent beds of stratified rocks, 

 perhaps raising them to a greater or less extent, but apparently not 

 changing the horizontal portion of the Cretaceous beds, which are all 



