298 A. G. LEONARD DRAINAGE CHANGES IN NORTH DAKOTA 



above the river and the upper portion of it is in many places composed 

 of glacial gravel and good-sized boulders. A railroad cut in this terrace 

 a mile northeast of Mandan, near the cemetery, shows the following 

 section : 



Feet Inches 



Soil 2-3 



Boulders and gravel 5-9 .... 



Sand, finely laminated, with several thin layers of gravel 2-5 .... 



Boulders and pebbles 6-12 



Lance beds, exposed above railroad track 15 .... 



In another cut less than one-quarter of a mile south a bed of boulders, 

 many of them several feet in diameter, mixed with gravel and resting on 

 the Lance beds, extends a distance of at least 100 } r ards along the railroad. 



Several miles south of Price the upper part of the terrace is composed 

 of boulders and coarse gravel, the deposit having a thickness of 5 to 6 

 feet. Between Sawyer and Price the terrace is finely developed and is 

 covered in some places by a layer of gravel and boulders ; in other places 

 by unstratified glacial drift or boulder-clay. In the vicinity of Hensler 

 the Missouri Valley is several miles wide, and here, as well as in other 

 places, numbers of low, rounded drift hills, covered with numerous 

 boulders, rest on the valley floor. Some of the railroad cuts show the 

 boulder-clay to be 30 to 40 feet thick. 



Before the time of the earlier ice-invasion, when the ice-sheet advanced 

 40 to 50 miles beyond the Missouri River, that stream must have flowed 

 in its present broad, terraced valley, and on the floor of this valley the 

 glacier deposited the boulders, gravel, and till so well exposed at many 

 points. These deposits, shown in the railroad cuts of the terrace, lie 

 about 40 feet above the ordinary stage of the river and vary considerably 

 in thickness. 



C. M. Bauer believes that during late Tertiary time the Missouri River 

 flowed northeast from Poplar. Montana, and that its Avaters finally 

 reached Hudson Bay. 5 Also that the Yellowstone flowed northward from 

 Williston by way of the valley of Muddy Creek. But it has been shown 

 that the present Missouri Valley in North Dakota is preglacial, and it is 

 doubtful whether the river in late Tertiary time had a course differing 

 from its present one. Additional evidence that the present valley is pre- 

 glacial, and that the trench of the river was excavated to its present depth 

 at the time of the earlier ice-invasion, is shown by the boulder bed less 

 than half a mile below the mouth of Tobacco Garden Creek. This bed of 



B C. M. Bauer : "A sketch of the late Tertiary history of the Upper Missouri River." 

 Jour. Geol., vol. xxiii (1915), pp. 52-58, 



