irayden.] ^<J^ [Oct. 2. 



lakes the water is evaporated, so that in the Autumn the bottoms 

 are dry and covered with a white incrustation which looks much 

 like water in the distance. One of these lakes still contained 

 water and seems to have a fair supply at all seasons. It is almost 

 a mile in length and half a mile in width. In the Spring these 

 lakes are quite large and are filled by the overflow of the 

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

 melting snows. Great quantities of fish are swept into these 

 lakes from the neighboring streams, and in the Autumn the 

 water becomes so alkaline by evaporation that the fish die in 

 great numbers along the shore. It is a curious fact that not a 

 single trout has ever been taken in any of the branches of the 

 North Platte unless a few have been caught in the Sweet-water, 

 while the branches of the -South Platte are filled with them. 



After entering the foot hills of the mountains the Big Lara- 

 mie and its branches wind their way through the narrow vallej's 

 or gorges formed by the anticlinals and synclinals produced by 

 the upheaval of the unchanged rocks. 



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

 red color, with only three layers of a light gray sandstone. No 

 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 red color from 

 the fact that the sediments were doubtless derived from the dis- 

 integration of the red sienitic rocks upon 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 

 above are Jurassic. 



Lying above the supposed Jurassic and beneath the well de- 

 fined Cretaceous there is a large thickness of sandstone which I 

 have called Transition beds or No. 1 (?), because they occupy 

 the position of the lower Cretaceous No. 1, as shown on the Mis- 

 souri River and in Middle Kansas. These beds are well devel- 

 oped 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 deter- 

 mine 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 characters of the sedi- 

 ments which compose them justify the name. 



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

 five miles south-west of Fort Sanders and about fifteen miles 



