THE TEMPORARY MISSISSIPPI RIVER 427 



of the abandoned channel south of Columbus Junction, he states 

 that 



The abandonment of the lower end of the channel from Colimibus Junction 

 southward probably cocurred as soon as the ice sheet had withdrawn sufficiently 

 to uncover the present line of the stream, for the altitude along the present 

 Mississippi bluffs is a few feet lower than the beds of the abandoned channel. 

 This lower altitude along the Mississippi is due to the incomplete filling of the 

 preglacial channel by drift.' 



Concerning Goose Lake channel, he concludes that its occupancy 

 "may have continued down to Wisconsin time.'"' Carman^ is 

 of the opinion that Goose Lake channel and Mud-Elkhorn-Mud 

 Creek Valley were followed for only a short time after the retreat 

 of the Illinoian ice sheet. Udden"* also does not favor the view 

 that the channel south of Columbus Junction was occupied for 

 any considerable time, although he is of the opinion that Mississippi 

 River did follow the Cedar River part of the temporary Mississippi 

 River until the lowan ice incursion. Udden believed that Cedar 

 River Valley between Moscow and Columbus Junction had lost 

 its river-like character and had taken on the form of a lake very 

 similar to that of Lake Pepin in the Mississippi River at the mouth 

 of the Chippewa River. To this wide expanse of water, Udden 

 gave the name "Lake Calvin" in honor of its discoverer, Samuel 

 Calvin. 



Recent work by the writer on the origin and history of extinct 

 Lake Calvin has convinced him that the former Mississippi River 

 follov/ed the westernmost course for a long period of time, perhaps 

 to the time of the lowan glaciation. 



NEW FACTORS BEARING ON THE DURATION OF THE TEMPORARY 

 MISSISSIPPI RIVER 



The duration of the temporary Mississippi River involves two 

 factors which up to the present time have received no consideration. 

 They are (i) extinct Lake Calvin and (2) Illinoian gumbotil. 



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

 (1899), pp. 96-97. 



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

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



5 J. Ernest Carman, "The Mississippi Valley between Savanna and Davenport," 

 Illinois Geol. Survey, Bull. 13 (1909), p. 62. 



" J. A. Udden, " Geology of Muscatine County, ''Iowa Geol. Survey, Vol. IX (1899), 

 P- 355- 



