GEOLOGICAL SURVEY OF THE TERRITORIES. 51 



former running north toward Fort Bridger, the latter northwest. Both 

 have carved out for themselves wonderfully deep and picturesque val- 

 leys. They can hardly be called gorges or canons from the fact that 

 the sides are not usually vertical. In some places there are large semi- 

 circular indentations in the sides of the valley, caused by the sliding 

 down of masses of earth ; and in looking down from the plateau above, 

 the eye meets with beautiful lakes, surrounded by small groves of pine or as- 

 pen. In the sides of the valley the strata may be studied with great clear- 

 ness, usually inclining at a greater or less angle. These valleys are largely 

 those of erosion, but not entirely so. The waters in former times have 

 cut through a vast thickness of strata at right angles, but a portion of 

 the way the valley lies between the riclges of upheaval, which I have 

 termed monoclinals. Some of the smaller branches start in the mono- 

 clinal intervals, and flexing around northward cut through the ridge at 

 right angles to the plains. In one instance a small branch of Black's 

 Fork starts between two ridges of carboniferous limestones, wears out a 

 valley eight hundred feet in depth and an eighth of a mile in width, 

 flows a little north of east into the main branch, which runs about due 

 north. At the same point commences a small branch of Bear River 

 between the same two ridges of limestone, and flows a little northof 

 west into one of the east branches of Bear River, although these two 

 small branches run in opposite directions. The ridge of separation is 

 not thirty feet above the principal valleys of Black's Fork and Bear 

 River. There is another interesting feature just here which should be 

 noticed. These small branches, four in number, completely isolate a 

 large fragment of the limestone ridge. It rises up in the form of a cone 

 eleven thousand feet above the sea, and seven hundred and fifty 

 feet above the valley at its base. The inclination of the limestones 

 is 45° to 50° northwest. 



There are two important thoughts suggested by the study of this 

 upper belt. First, the amount of debris found by the broken fragments 

 of the sandstone and quart;*tes is immense, beyond any instance I have 

 observed before. Not only the ridges, but also the sides of the deep 

 valleys, are covered to an unknown thickness with fragments of quartz- 

 ite, sandstone, and limestone, of all sizes from that of a pea to several 

 cubical feet. Scattered over the surface of valley and ridges are also 

 great quantities of the same rocks in a more or less worn condition, and 

 the deposit of drift which extends up to the third belt, close to the 

 crest, and varies in thickness from a few feet to 1,000 or 1,200, is 

 composed to a great extent of these rocks. Along the northern slope of 

 the Uinta Mountains, extending into the plains, these worn rocks cover 

 an area at least one hundred miles in length from east to west and fifty 

 from north to south. These stray masses are more worn, the further 

 we recede into the plains northward from the mountains. In the 

 region of Echo and Weber Creeks is a vast deposit of conglomerate, 

 probably three thousand to five thousand feet in thickness, the most re- 

 markable group of rocks of that character I have ever seen on this con- 

 tinent. The question has often arisen in my mind from whence the 

 materials were derived. I cannot answer the question even yet, but 

 the debris of the Uinta Mountains, if transported to some lake basin, 

 would make a mass of conglomerate of equal thickness and cover 

 an equal area. 



The second thought suggested is the apparently excellent illustration 

 of the gradual transition from unchanged to changed or metamorphic 

 rocks. We have a thickness of about one thousand feet of carboniferous 

 limestones unchanged. Passing upward to the crest of the mountains, 



