GEOLOGICAL SURVEY OF THE TEREITORIES. 85 



branches of the Big Laramie, which are greatly swollen by the melting 

 snow. Great quantities of fish are swept into the lakes from the neigh- 

 boring streams, and in the autumn the water becomes so alkaline by 

 evaporation that the fish die in great numbers along the shores. It is a 

 curious fact that not a single trout has been taken from any of the 

 branches of the North Platte, unless a few have been caught in the 

 Sweetwater, while the little branches of the South Platte are filled with 

 them. 



After entering the foot-hills of the mountains the Big Laramie and 

 its branches wind their way through the valleys or gorges formed by the 

 anticlinals and synclinals, produced by the upheaving of the unchanged 

 rocks. All the lower beds are more or less arenaceous and of a brick- 

 red color, with only three layers of light-gray sandstone, i^o fossils can 

 be found in any of the rocks, so that it is difficult to determine their age 

 with certainty. We believe that the lower beds are Carboniferous, and 

 have received their color from the fact that the sediments were doubt- 

 less derived from the disintegration of the red syenitic rocks upou which 

 they rest. It is also quite possible that a portion of the red beds are 

 Triassic, and also that the yellow, gray, and rusty sands and sandstones 

 alone are Jurassic. Lying above the supposed Jurassic, and beneath the 

 well-defined Cretaceous, there is a considerable thickness of sandstones, 

 which I have called transition beds, or No. 1, because they occupy the 

 position of the Lower Cretaceous aSTo. 1, as shown on the Missouri Eiver 

 and in Middle Kansas. These beds are well developed and quite uniform 

 in their lithological character all along the mountain-sides, from latitude 

 49° to the Arkansas, yet they have never yielded a single characteristic 

 fossil that would determine their age. I have, therefore, called them, 

 provisionally. Lower Cretaceous, or beds of transition from one great 

 period of geological history to another, and the character of the sedi- 

 ments which compose them justify the name. 



Near our camp on the Big Laramie, which was about thirty-five miles 

 southwest of Fort Sanders, and about fifteen miles above the foot of the 

 hills, were some singular illustrations of the dynamics of geology. On 

 the southwest side of the stream, and inclining eastward or southeast- 

 ward, the entire series of red and variegated beds are shown in their 

 order of succession, 1,500 or 2,000 feet in height. At the foot of this 

 escarpment is a low. ridge of the red material, which is so grassed over 

 that the connection cannot be seen with the syenitic nucleus. Then 

 comes a belt of syenite, about 200 yards wide and three to five miles 

 long, the jagged masses of rock reaching a height of 1,000 feet or more, 

 and standing nearly vertical, or dipping slightly to the southeast. 

 Between the syenitic beds and the river are two low ridges of Cretaceous 

 Nos. 2 and 3, which seem to have been lifted up with the syenitic, but 

 to have fallen back, past a vertical position, so that they now incline 

 from the syenitic ridge, while on the opposite side the beds have a reg- 

 ular dip from the ridge. This peculiarity seems to be common in various 

 localities, owing to the fact that the metamorphic beds, which compose 

 the central portions of all the mountains, had suffered upheaval prior 

 to the deposition of the unchanged beds. Therefore, in the quiet eleva- 

 tion of the mountain-ranges, the beds are merely litted up in the direc- 

 tion of the dip of the older rocks, while they are, as it were, pushed 

 away from the opposite side, forming what may be called an abrupt or 

 incomplete anticlinal. 



On the opposite, or south side of the river, there is a gradual slope 

 for 2,000 feet along the bed of the stream, the strata inclining 5°, until 

 we reach the nucleus of another mountam-range : so that we have here, 



