426 WALTER H. SCHOEWE 



ABANDONED CHANNEL SOUTH OF COLUMBUS JUNCTION 



The abandoned channel south of Columbus Junction was dis- 

 covered by Leverett as early as 1896. This channel, which is 

 outlined on Figure i, has been described in detail by Leverett 

 in his monograph on the Illinois glacial lobe/ The channel 

 extends southward from Columbus Junction for a distance of 

 12 miles to the vicinity of Winfield. Separating into two branches 

 at this point, its course continues westward to the valley of Skunk 

 River at Coppock. Thence the temporary course of the Mississippi 

 is southward for a distance of 18 miles to the bend of the Big Cedar, 

 where it leads southeastward across Lee County to the valley of 

 Mississippi River at Viele, 6 miles below Fort Madison. 



This ancient valley of the Mississippi is incised below the general 

 upland surface of the Kansan drift plain 30 to 60 feet. The valley 

 floor rises 120 feet above the level of Iowa River at Columbus 

 Junction, where it lies at an elevation of about 700 feet above sea 

 level. Its general width ranges from ij to i| miles. The valley 

 is well defined but is more conspicuous the farther southward it 

 is traced. At the divide in Sections 35 and 36 of Elm Grove 

 Township, Louisa County, 7 miles south of Columbus Junction, 

 the valley floor is i mile wide and 35 to 40 feet below the general 

 upland level. Several miles south of Columbus Junction bedrock 

 appears in the valley walls and that part along Skunk River is cut 

 largely in solid rock. It has been estimated that the excavation 

 along the channel from Columbus Junction to Viele amounts to 

 one-half a cubic mile.^ Unusual deposits of sand and gravel are 

 lacking in the channel. 



VIEWS REGARDING THE DURATION OF THE TEMPORARY 

 MISSISSIPPI RIVER 



Concerning the general displacement of the Mississippi River 

 by the Illinoian ice sheet, Leverett states that "with the recession 

 of the Illinoian ice sheet the Mississippi shifted to its present course 

 between Clinton and Fort Madison.^ And in speaking particularly 



' F. Leverett, "The Illinois Glacial Lobe," U.S. Geol. Survey, Monograph 

 XXXVIII (1899), pp. 91-93. 



^ F. Leverett, op. cit., p. 93. 



3 F. Leverett, "Outline of Pleistocene History of Mississippi Valley," Jour, of 

 Geol., Vol. XXIX (1921), p. 622. 



