40 J. E. TODD — HYDKOGRAPHIC HISTORY OF SOUTH DAKOTA 



Thus we have found the history very interesting, even in outline. 

 When further research shall have gathered up the details it will doubt- 

 less become much more so. The region around the Black hills and 

 about the margin of the drift may prove to be the most instructive areas 

 for research. We may hope thereby to correlate, more satisfactorily 

 than has been done, the movements of the ice-sheet with the history of 

 the Rocky Mountain axis. We may hope also for further light on the 

 relations of the loess to both. 



