EVIDENCE OP POSTGLACIAL AGE OP LITTLE MISSOURI 303 



the Little Missouri is much younger than the portion above the mouth 

 of Bowling Creek, and that it has been formed since the ice-invasion of 

 the Glacial period. The following are some of the reasons for believing 

 it to be postglacial, or at least post-Kansan : 



1. The great majority of the tributaries of the lower Little Missouri 

 below Bowling Creek are short — much shorter than those above. Most 

 of them are not over two or three miles in length, while the tributaries 

 of the river for 60 miles above Bowling Creek are from four to eight 

 times as long, since they have had a much longer time to lengthen by 

 headward erosion. 



2. Closely connected with the length of the tributaries is the width of 

 the badlands, which are formed by the erosion of the Little Missouri 

 Eiver and the streams flowing into it. Below Bowling Creek the bad- 

 lands in most places are not over five to seven miles wide, at some points 

 extending back only two or three miles from the river on either side, 

 while along the river above Bowling Creek the belt of badlands has a 

 width of 15 to 25 miles. 



3. One of the conspicuous features of the Little Missouri Valley in 

 Billings County and for a few miles of its course in southern McKenzie 

 County are the high, broad flats or terraces on one or both sides of the 

 river. They have an elevation ranging from 240 feet at the south to 

 nearly 300 feet above the river at the north and are one to two miles 

 and over in width. They were undoubtedly formed prior to the Glacial 

 period. These high terraces are wholly absent from the lower valley, 

 which would seem to indicate that this portion is more recent and was 

 formed since the region was elevated, so that the rejuvenated river cut its 

 inner valley several hundred feet below the floor of its earlier one. 



4. The fact that the Little Missouri Eiver leaves its preglacial valley 

 and turns east at a point which coincides closely with the southern bound- 

 ary of the ice-sheet, and that for over 40 miles the new valley follows 

 quite closely the former ice-sheet margin, suggests that the latter gov- 

 erned to some extent at least the location of the lower valley of that 

 river. The old valley was blocked with ice as far south as the point where 

 the Little Missouri abandons it, and the waters, when forced to seek a 

 new channel, eventually made their way east not far from the edge of 

 this ice-sheet, and the river thus cut its valley along this eastward course. 



5. The Killdeer Mountains, in northwestern Dunn County, are flat- 

 topped buttes or mesas, rising from 500 to 650 feet above the surround- 

 ing upland plain and nearly 1,200 feet above the Little Missouri Eiver. 

 They lie less than six miles south of the latter, and it does not appear 



