XX FISHES OF ILLINOIS 



have no relation to them. When the Wisconsin streams broke 

 through their confining moraines, they had to find their way to the 

 most accessible Illinoisan stream as best they could. 



The present condition of the area of the Wisconsin drift with its 

 almost unbroken moraines, its black level prairies, peat bogs, lake 

 beds, shallow streams, and incomplete drainage is believed to 

 represent faithfully the condition of the Illinoisan area at an earlier 

 period in its history, and this correspondence enables us to interpret 

 many topographic relations in this area which would not otherwise 

 be apparent. For instance, the control which the moraines of the 

 -Wisconsin area exercise on the direction of its streams, the position 

 and size of its lakes, and the location and form of the tracts of black 

 prairie soil are very evident, and it is believed like control would be 

 just as evident in the Illinoisan area if the fragments of its moraines 

 -were carefully studied and mapped so that they could be restored 

 and their influence shown. All that has been said about the early 

 history of the Illinoisan area applies as well to the Wisconsin. The 

 only material differences between them are due to age and conse- 

 quent degree of development. 



THE UNGLACIATED SOUTHERN AREA 



A natural division of this area would be into mountain ridge and 

 coastal plain. Regarding the first, little need be mentioned beyond 

 the facts that it is a true mountain in structure, although its altitude 

 is low (about 400 feet, on an average, above the general level) ; that 

 it is composed almost entirely of limestones and sandstones of sub- 

 carboniferous age; and that it presents on its southern slope the 

 only approach to volcanic phenomena in the state. That portion 

 of the state south of the Ozarks forms part of the coastal plain 

 which borders the Atlantic and Gulf coasts. It has all the peculiari- 

 ties of this plain, since it is level, sandy, and covered with residual 

 soils. It is almost entirely drained by the Cache and Big Bay 

 rivers, principally the former, whose current, owing to a reef across 

 the channel near Ullin, is very sluggish. 



THE RIVER SYSTEMS 



With these general principles in mind we come to a more detailed 

 description of the drainage basins of the principal streams. Nearly 

 the entire surface of the state is drained by two sets of streams, viz. : 

 the Rock, Illinois, Kaskaskia, and Big Muddy rivers, direct tributa- 

 ries of the Mississippi, whose general direction is southwest ; and the 

 Saline, Little Wabash, Embarras, and Vermilion, tributaries of the 



