THE 



JOURNAL OF GEOLOGY 



SEPTEMBER-OCTOBER, ign 



PRELIMINARY STATEMENT CONCERNING A NEW 



SYSTEM OF QUATERNARY LAKES IN THE 



MISSISSIPPI BASIN 1 



EUGENE WESLEY SHAW 



U.S. Geological Survey 



It is a significant fact that in but few places do the Mississippi 

 and Ohio rivers flow on consolidated rock. Throughout most of 

 their courses they flow over bodies of silt, sand, and gravel 50-100 

 feet in thickness. The lower half or third of each tributary also 

 flows over a thick unconsolidated mass, which is similar to those 

 on the larger streams, except that in general it is less coarse. For 

 examples, the Wisconsin River in southwestern Wisconsin is 

 working 50 feet or more above a hard rock channel; Big Muddy 

 River in southern Illinois flows between mud banks in a broad, 

 shallow valley with a buried channel 40 feet below; and away east 

 in Pennsylvania the Monongahela does not flow over bed-rock 

 at any point within the limits of the state. Thus, not only the 

 valleys of the Mississippi and Ohio, but the lower part of almost 

 every tributary valley in the northeast central states, and probably 

 in a considerably larger territory, is partly filled with loose sedi- 

 ment, and in Illinois, Indiana, and Kentucky the filling on the 

 tributary streams consists largely of clay, a brief description and 

 interpretation of which are the objects of the present paper. 



1 Published by permission of the Director of the U.S. Geological Survey, Washing- 

 ton, D.C. A more complete description is to be published by the 111. Geological 

 Survey. 



