peale.] GEOLOGY EAGLE EIVER. 81 



Eagle, when they descend rapidly to its level. The erosion along the 

 main stream has been much greater for several reasons. In the first 

 place the beds have a dip from the mahi range, leaving, perhaps, a sort 

 of trough between the Sawatch range and the Park range. This de- 

 termined the course of the river, which we accordingly find curving 

 around the range as the sedimentary formations do. These beds are 

 also in a great measure made up of sandstones that are comparatively 

 soft, and yielded readily to the action of water. The river, therefore, is 

 in a monoclinal rift for a considerable portion of its course. 



In the canon, above the mouth of Roche-Moutonnee Creek, the streams 

 reach th e river by falls and cascades. 



The slopes are heavily timbered with dense pine forests, and along 

 the streams are groves of cottonwood, (Populus tremuloides.) In the 

 canon are huge bowlders, which, mingled with the dead and fallen 

 timber where the forest has been swept by fires, cause great difficulty 

 in traveling. 



At the mouth of the Piney, a stream coming in from the east, the 

 river again enters a canon. It is something over a mile in length. At 

 the head of the canon is a high bluff on the right side, while the op- 

 posite bank is broken down, allowing the passage of the trail over the 

 hill, not very far above the level of the water. 



On the south side, on the top of the quartzite, (Potsdam *?) are lime- 

 stones, and, a short distance below, the Carboniferous sandstones cross 

 the river, the angle of inclination being about 25°, a little more to the 

 northward than in the bluffs opposite Roche-Moutonnee Creek. 



Below the canon the Eagle enters a broad valley, extending for ten 

 miles, to the head of another canon. This valley will probably average 

 a mile in width, and is filled with the debris washed from the hills on 

 either side. It is terraced and covered with a growth of sage-brush, 

 (Artemisia.) Bordering the river is a narrow belt of alluvium which 

 widens in the lower part of the valley around two small lake-expan- 

 sions of the stream. There are beautiful meadows around the lakes. 

 The lower lake is about a mile long and an eighth of a mile wide, while 

 the upper one is much smaller, being only a little over a half a mile in 

 length. 



Here we found a party of men camped. They were prospecting and 

 fishing. Eagle Biver abounds in delicious trout of a large size, some 

 that we measured being sixteen inches in length. Their plan was to 

 take the fish every week to Oro City, on the Arkansas River, and sell 

 them. They also claimed to have found gold in some of the streams 

 coming from the Sawatch range. The gold, if present, is probably de- 

 rived from the granitic and gneissic rocks that prevail near the heads of 

 the creeks. 



The course of the Eagle through the valley we have just described is 

 north 78° west. On the southwest side, the long sloping spurs that we 

 noticed above the Piney still continue. Near the river they are lower, 

 and, for the most part, grassed over, only an occasional outcrop of lime- 

 stone or sandstone appearing. On the opposite side are outcrops of 

 red sandstone (Triassic'?). I have referred to the canon which bounds 

 the lower end of the valley. It is somewhat curious. On entering it the 

 river changes its course and flows north 45° west, which direction it keeps 

 for four miles. It then turns abruptly and flows south 72° west. This 

 portion of its course in the canon is three miles in length. On the south 

 side is a semicircular ridge, extending from the head of the canon to its 

 foot. It reminds one of a bow, while the river, with its bend, is the 

 cord ready drawn to discharge the arrow. We made two stations on 

 6H 



