58 CLYDE MAXWELL BAUER 



marginal drainage proceeded when the ice was at its maximum in 

 eastern Montana and western North Dakota is at present a matter 

 of conjecture. However, it is probable that it flowed southeastward 

 across cols and through various preglacial valleys until it joined 

 the Mississippi/ 



After the retreat of the ice, the Upper Missouri, the Yellowstone, 

 and the Little Missouri, owing to the glacial debris, no longer found 

 an outlet to the north, but instead followed in part the glacial 

 drainage and in part the preglacial stream courses southeastward to 

 the Gulf of Mexico. 



■ ^ J. E. Todd, "The Pleistocene History of Missouri River," Am. Assoc. Adv. Sci. 

 Proc, N.S., XXXIX (1914), 263-74. 



