466 THE ILLINOIS GLACIAL LOBE. 



have been divided among the several lines referred to above renders it diffi- 

 cult to estimate the work accomplished. It, however, helps us to appreciate 

 the cause for the exceedingly small amount of excavation accomplished by 

 the stream in its present course. It also suggests an explanation for the 

 greater amount of excavation accomplished in the removal of the Fairport 

 divide, since the entire energies of the Mississippi appear to have been 

 expended on that divide throughout the time since the course across the 

 Leclaire Rapids came into operation. 



In the discussion of the temporary displacement of the Mississipjn into 

 a course outside the limits of the Ulinoian drift (which seems to have 

 occurred during the culmination of the Ulinoian invasion), it was suggested 

 that the Mississippi may have maintained its flow through the lower courses 

 of the Cedar and Iowa rivers, until the invasion of the ice from the west at 

 the Iowan stage of glaciation forced it into a course farther east. If this 

 suggestion proves true, the establishment of the present course of the 

 Mississippi across the Leclaire Rapids, and also the occupancy of the aban- 

 doned channels, Cattail Slough and Meredosia Slough, may be referred 

 with some'confidence to the Iowan stage of glaciation. Possibly the Rock 

 River drainag*e had been opened westward past Fairport at an earlier date, 

 though it seems quite as probable that Rock River would have connected 

 either to the west, through the Meredosia Slough, with the Mississippi, or 

 passed southward into the Illinois, as it appears to have done in preglacial 

 time. The complexity of the channeling- is such as to demand further field 

 examination or further deliberation before a satisfactory interpretation can 

 be set forth. 



The question of the preglacial course of the Mississippi below Clinton 

 remains to be considered. Udden's special investigation has led him to the 

 conclusion that the preglacial line must have been along one of two courses, 

 either southeastward through the Meredosia Slough and Green River Basin 

 to the Illinois at the bend near Hennepin, or directly westward through the 

 Wapsipinnicon Basin to the mouth of Mud Creek, and thence southwestward 

 along the Mud Creek sag to the Cedar; thence the course may have been 

 by way of the present Cedar and lower Iowa, or more directly southward 

 to the Mississippi just west of the meridian of Muscatine. Udden has col- 

 lected well data along the Mud Creek sag showing that a buried channel 

 occurs there whose rock floor is more than 100 feet below the level of the 



