270 THE ILLINOIS GLACIAL LOBE. 



CHARACTER OF THE OUTWASH. 



The writer's examination of the features on the outer border of the 

 Bloomington morainic S3 r stern covers the portion from Bloomington north- 

 ward, and the discussion pertains chiefly to that portion. The portion east- 

 ward from Blooming-ton was examined some years since by Prof. R. D. 

 Salisbury, but has received scarcely any attention from the writer. 



It will be observed that the Bloomington morainic system forms the 

 source of several streams whose courses are southward or westward from it 

 through the outer-border district. It also forms the source of other streams 

 which lead northward or eastward or southeastward through the inner- 

 border district. Still other streams flow through this morainic system from 

 the inner into the outer border district. Of the first class the several head- 

 water forks of Wabash- Vermilion River, Sangamon River, Salt Creek, the 

 two Kiekapoo creeks, Sugar Creek, Green River, and the two forks of Kish- 

 waukee River are worthy of mention. Of the second class, Iroquois River, 

 the Illinois-Vermilion River, Bureau Creek, and the western tributaries of 

 Fox River are illustrations. Of the third class the Illinois and Mackinaw 

 rivers are the only examples in Illinois. 



An examination of these valleys brings to light important contrasts. 

 The streams which flow away from the outer border of the moraine are in 

 most instances found to occupy valleys which had been excavated somewhat 

 by streams which antedated the formation of this moraine. These valleys 

 received the outwash from the moraine and were partially filled by it. The 

 streams on the inner border of the moraine had not the advantage of 

 previously formed valleys, and in consequence their channels are entirely 

 the result of stream action since the withdrawal of the ice sheet from this 

 morainic svstem. It is found that the valleys which lead away from the 

 moraine through the outer-border district have in most instances a filling of 

 o-ravel or sand which is definitely connected with the morainic svstem as an 

 outwash from the ice sheet. The streams which lead from the moraine 

 across the inner-border district are not thus characterized by sand-and- 

 gravel filling. In some cases the streams issuing from the edge of the ice 

 sheet had sufficient force to transport gravel for many miles away from the 

 ice border. In other instances they were able to carry the gravel but a few 

 miles, as shown in the discussion below. The extent of the gravelly and 



