12 ERA NK LE VERE TT 



Filling at the Illijioian stage of glaciation. — Following this great 

 erosion there came a partial filling of the part of the valley imme- 

 diately outside the limits of the Illinoian drift sheet. It is well 

 displayed below the rapids, and some remnants are to be seen 

 along the borders of the rapids. This filling appears to have 

 occurred at the Illinoian stage of glaciation. Evidence of this 

 relationship is to be found in the connection, or close association, 

 of this filling with the opening of a temporary course for the 

 Mississippi across southeastern Iowa, which occurred at the time 

 the Mississippi valley above the rapids was covered by the 

 Labrador ice-field. 



The drainage line referred to leaves the present Mississippi 

 at the mouth of the Maquoketa, passes southward along that valley 

 (reversed) to " Goose Lake channel," and thence to the Wapsipin- 

 nicon Valley, connecting with it a few miles above its present 

 mouth. It follows up theWapsipinnicon a few miles to the mouth 

 of Mud Creek, a southern tributary, which, together with a small 

 tributary of Cedar River, also called Mud Creek, furnishes the line 

 of continuation for the old valley to the Cedar River near the 

 great bend at Moscow. The valley continues southwest to the 

 Iowa River along the course now followed by the Cedar in its 

 lower twenty-five miles. It then passes southward from Colum- 

 bus Junction to Winfield, and thence westward to Skunk River at 

 Coppock, opening in its westward course two lines, one of which 

 is now utilized by Crooked Creek. From Coppock the old drain- 

 age line follows the course of Skunk River southward to Rome, 

 and Cedar Creek (reversed) to Salem. It there turns south- 

 eastward, being known as "Grand Valley" in northern Lee 

 county, and joins the Mississippi about six miles west of Fort 

 Madison, nearly opposite the head of the rapids. Its continua- 

 tion was evidently across the rapids into the broad valley below 

 Keokuk. 



The altitude of the bottom of this old valle}^, near the head 

 of the rapids, is fully ioo feet above the present stream, but con- 

 nects well with the surface of the valley filling in and below the 

 rapids. It is nearly ioo feet lower than at the point where it 



