7o6 S. R. CAPPS AND E. D. K. LEFFINGWELL 



The history of the change seems to be as follows : As the ice of the 

 last glacial epoch came down the valley of Homestake Creek, it 

 pushed across the valley then occupied by the Eagle (Fig. 2, b) and 

 by obstructing the stream, ponded it, and caused it to find a new 

 outlet to the north. On the retreat of the ice, a drift dam was left 

 across the old valley, and the Eagle continued to occupy its new 

 channel as far as Redcliff, where it re-enters its old valley. 



The second case is that of the Arkansas River, ^ the course of 

 which was changed by the ice of the earlier (next before last) epoch of 

 glaciation. The ice, advancing down the valleys of Lake and Clear 

 Creeks, pushed across the Arkansas valley to the slope on the east 

 side, and crowded the river up against the granite walls on that side, 

 and even shifted it up somewhat on the other slope (see Fig. i). At 

 these places the river cut a new channel in the rock. From data 

 gathered from borings at the placer mines west of Granite, it appears 

 that the surface of the rock declines to the west for a considerable dis- 

 tance west of Granite (Fig. i), indicating that the preglacial channel 

 of the river was some distance west of the present river bed between 

 Twin Lakes and Clear Creek. The river, being pushed over to the 

 east at two points, may have had, at first, a great loop to the west 

 between these points. If so, the curve may have been cut out and 

 the channel straightened by piracy, or it may have been crowded 

 over between the ice lobes, by fluvio-glacial deposition. 



S. R. Capps. 

 E. D. K. Leffingwell. 



The University of Chicago. 



^ Professor L. F. Westgate, of Ohio Wesleyan University, was working upon this 

 problem when the writers entered this portion of the field, and it is understood that he 

 will publish his results on this problem in the near future. He had worked out the 

 essential features of the changes in the channel of the Arkansas before the writers 

 reached this part of their field. 



