472 J. E. TODD THE CHANNEL OF THE MISSOURI RIVER 



the moiitli of the latter stream, but joins the Missouri four miles to the 

 uorth. There is no reason for believing that the Knife River ever joined the 

 Missouri near Fort Stevenson, and the lower valley of this stream has every 

 appearance of great age, having a broad floodplain* and gentle slopes. It is 

 clearly a preglaciul valley. The Heart River is thus the only important 

 tributary of the Missouri which might have continued eastward to the James 

 River if the valley of Apple Creek, which has its mouth just opposite the 

 Heart, is an indication of this. But Apple Creek is readily accounted for 

 as a preglacial tributary of the Missouri and one of the chief outlets for the 

 glacial waters when the ice-margin occupied the position marked by the 

 Altamont moraine. Its valley is largely filled with glacial outwash from 

 the moraine." 



2. "There is abundant evidence that the Missouri Valley beloM' the mouth 

 of Shake Creek is preglacial, and that the river was not forced by the ice- 

 sheet to take its present southerlj- course through North Dakota. This evi- 

 dence is based on the presence of glacial boulders on the valley bottom and 

 at many points on a terrace representing a former floodplain of the Missouri. 

 Boulders have been encountered in two wells in Bismarck at a depth of 125 

 feet below the surface or 80 feet below river level. These wells are near 

 the edge of the terrace bordering the Missouri Valley at Bismarck, and since 

 the boulders rest on the bedrock they indicate that the valley was excavated 

 to this depth prior to the Glacial period. In several borings made for the 

 Northern Pacific Railroad previous to the building of its bridge across the 

 river at Bismarck, from TO to 80 feet of silt and gravel were passed through 

 before reaching the bedrock, and in one boring a boulder was struck at a 

 depth of about 50 feet below the river bed." 



3. "On the west side of the Missouri Valley, between Mandan and the 

 mouth of the Knife River, there is a w^ell developed terrace which in places 

 is a mile and more wide. This terrace has an elevation of 55 to 60 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. Inc'aes.' 



Soil 2-3 



.Boulders and gravel 5-9 



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



Boulders and pebbles (>-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 yards 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." 



4. "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 



