THE VALPARAISO MORAINIC SYSTEM. 375 



and gravel. In the portion west of the river till apparently predominates 

 over sand and gravel, though the inner border is in places quite sandy. 



CHARACTER OF THE OUTWASH. 



The position of the Valparaiso morainic system is favorable for the 

 discharge of water from the western and southern borders and to some 

 extent from the eastern border. On the west the Fox, Dupage, and Des 

 Plaines rivers, and small tributaries of the Des Plaines, lead directly away 

 from the border of the morainic system, while on the south the Kankakee 

 and its tributaries affoi'd a line of discharge toward the west. On the east 

 the streams now draining the border of this morainic system are tributary 

 to rivers which flow through it into Lake Michigan, but it seems probable 

 that for at least a portion of the time of the formation of the Valparaiso 

 morainic system the drainage along Dowagiac River and also much of the 

 St. Joseph River was tributary to the Kankakee instead of the lower St. 

 Joseph River. 



Along each of the main valleys which border the morainic system, or 

 lead away from it, a large amount of gravelly material has been deposited. 

 Taking these valleys in turn, beginning with Fox River and passing south 

 and east, the features are as follows: 



On Fox River, from the Wisconsin line southward nearly to the south 

 line of Lake and McHenry counties, there are broad marshes underlain by 

 sand and silt, and the stream has very little fall. Professor Rolfe's baro- 

 metric survey indicates that there is a fall of but 30 feet in the 30 miles 

 occupied in crossing these counties. In southeastern McHenry County 

 heavy deposits of gravel and cobble set in, which lead down the valley in 

 the form of terraces through the entire length of Kane County, a distance 

 of 30 miles. The stream in this distance makes a descent of 125 feet, 

 while the gravelly terraces make an even greater descent, their elevation 

 at Elgin being nearly 100 feet and at Aurora only 40 to 50 feet above the 

 stream. Heading as these gravel deposits do near the point where the 

 Valparaiso moraine leads away from the Fox River Valley, and standing as 

 they do above the marshy tracts along the portion of the valley imme- 

 diately to the north, there seems to be little question that they represent an 

 outwash from the ice sheet. The gravel is of medium coarseness through- 

 out the greater part of its depth, but in places the surface portion consists 



