PREGLACIAL MOINGONA RIVER 



557 



but below the general bed-rock plain did not seem to suggest 

 to him that they really indicated paths of old rivers. In his 

 misinterpretation originated much of the confusion which long 

 existed concerning the presence of an lowan drift sheet in the 

 State. 



The relative magnitudes of the present Des Moines valley and 

 of the gorge of the Old Moingona river are well represented in 



Belfast 



MoNi 



Fig. 177. — Gorges of old Moingona, preglacial Mississippi and present 

 Mississippi River at Keokuk. 



cross-section at Des Moines, one mile above the mouth of the 

 Raccoon river (figure 176). 



A similar comparison of the old and new Mississippi rivers is 

 represented in cross-section (figure 177) based upon well data 

 and natural exposures around the mouth of the present Des 

 Moines river. The cross-section given by Prof. C. H. Gordon^'' 

 of the old Mississippi gorge at Keokuk exaggerates too much the 



Fig. 178.— Cross section from Sonora to Argyle, at mouth of Old Moingona 

 river, sliowing old and new gorges of tlie Mississippi river. (After Gordon). 



size of the ancient valley. As represented by this writer the 

 part ascribed to the old Mississippi river embraces b^oth that 

 stream and the old Moingona gorge, thus making the former 

 very much too large. It is quite probable that in pre-Glacial 

 times the old Moingona river was really the more important 

 stream of the two. 



»Iowa Geol. Survey, Vol. Ill, ,p. 248, 1895. 



