Jlayden.] ^^ • [Februaiy 19, 



tains wliicli bounds the west side of the south park, and flows about 

 north-east to Cache la Poudre, and there bends round slightly toward the 

 east and joins the main Platte. The littl^ branches that flow from the 

 mountain sides are very numerous, and each one cuts a tremendous 

 channel through the sides of the mountain, aflbrding most excellent sec- 

 tions of the strata for the geologist. Nearly all the branches that rise 

 in the plains have very wide valleys, but are mostly dry, especially in the 

 latter part of the summer and autumn. Although the Platte river is 

 never navigable at any season of the year, yet the area drained by it is 

 immense, at least 800 miles from east to west and 350 from north to 

 south, or an area of nearly 300, 000 square miles ; and yet the North 

 Platte is one of the minor branches of the Missouri river. 



The South Platte flows through the different formations along the 

 flanks of the mountain ; and in its course through the plains cuts the 

 lignite-tertiary for 50 miles or more, when the White river tertiary over- 

 laps the plains to the junction. 



The above brief remarks are intended principally to show by the 

 geography the gigantic scale upon which every thing in this Western 

 Country is planned, that even the district drained by the Platte and its 

 branches is larger than all New England, New York and Pennsylvania. 



September 1st, I left Fort Sanders with my party to examine the 

 country along the southern border of the Laramie plains. We passed 

 over the different beds of the cretaceous period for about 30 miles, until 

 we reached a point near Cooper's creek, when indications of the tertiary 

 begin to overlap the cretaceous. 



The examples of the erosive action of water along the northern side 

 of the mountains that border the Laramie plains are numerous. In the 

 valley of Cooper's creek near the foot of the mountains there is a trian- 

 gular space about five miles long, and two or three miles M'ide on the 

 south-west side. On the south side there is a hill 500 feet high, the sum- 

 mit of which is composed of drift, and the surface paved with partially 

 worn rocks. On the north-west side there is a long ridge, the top of 

 which is composed of the yellowish sandstones of cretaceous formation 

 No. 5, in which a few characteristic species of fossils, like Inoceramus, 

 occur. These ridges seem to converge about two miles below the Stage 

 Station, so that the creek passes through a sort of gorge. The valley of 

 the creek is covered quite extensively with drift materials derived from 

 the neighboring mountains. 



Six miles west of Cooper's creek we find the first good exposure of 

 coal. The upper cretaceous beds crop out occasionally in that vicinity, 

 but are overlapped by the coal bearing strata. 



The slopes are all so gentle and the superficial drift covers the country 

 to such an extent that I found it difficult to get a good section. No. 5 

 (cretaceous) seems to pass gradually up into the coal-bearing beds, and 

 the change in the sediments of the two systems is slisrht. 



What appears to be the lowest bed of the coal-bearing scries in this 

 region, is a brown grit, very loosely aggregated with, sometimes, irregu- 



