TEMPORARY DISPLACEMENT OF THE MISSISSIPPI. 9] 



Mud Creek.- The sag leaves the Wapsipirmicon a few miles east of Dixon 

 and comes to the Cedar River at its bend near Moscow, passing just west 

 of Durant and through Wilton. Its course may be seen by reference to 

 the Durant and Wilton Junction sheets of this Survey. The north end of 

 this portion of the valley was occupied by the Iowan ice sheet, which has 

 in a measure concealed its erosion contours, though the valley may still be 

 traced without difficulty. It is now thought to have been utilized by the 

 Mississippi at the Illinoian stage of glaciation. 



The point at which the Mississippi was deflected into this old channel 

 was probably at the mouth of the Maqnoketa (see glacial map, PI. VI), from 

 which point it had southward course through the Groose Lake channel, 

 brought to notice by McGee 1 , to the Wapsipinnicon, coming to that valley 

 near, the mouth of the Wapsipinnicon, as may be seen by reference to the 

 topographic map of that region, PL XVIII (in pocket). Perhaps the Missis- 

 sippi also occiipied its present channel from the mouth of the Maquoketa to 

 the mouth of the Wapsipinnicon. The only apparent objection to this view 

 is the possibility that the Illinoian ice sheet obstructed the present course of 

 the river. This being a region in which the Iowan invasion obliterated the 

 marginal features of the Illinoian drift it becomes a difficult matter, as 

 already noted, to determine the precise position of the Illinoian boundary. 

 It probably encroached but a few miles at most on the Iowa side of the 

 river above the mouth of the Wapsipinnicon. 



This abandoned course of the Mississippi can be studied to best ad- 

 vantage in the portion south from the Iowa River, as the northern portion 

 has been greatly modified by the Iowan ice invasion. The description, 

 therefore, begins at the point where the old channel departs from the Iowa 

 River. As above noted, the course of the channel is southward from just 

 above Columbus Junction to the vicinity of Winfield, a distance of 12 

 miles, crossing Long Creek, a small tributary of the Iowa, about 6 miles 

 south of Columbus Junction. The bed of the old channel is about 120 

 feet above the level of the Iowa River bottom at Columbus Junction, or 

 very nearly 710 feet above tide. It is cut to a depth of 25 to 35 feet below 

 the bordering plain, and has a width of 1^ to 1J miles. Its depth and 

 breadth are not much greater than that of the present Mississippi within its 



1 The drainage systems and loess of eastern Iowa, "by W J McGee, private publication, 1884. 

 Also the Pleistocene history of northeastern Iowa, by W J ilcGee, Eleventh Ann. Kept., U. S. Geol. 

 Survey, 1891, pp. 227, 228. 



