280 THE ILLINOIS GLACIAL LOBE. 



to have varied little during the long period in which the ice sheet dis- 

 charged waters into this basin. For a few miles along the immediate bor- 

 ders of the river below the point where the East Fork enters this basin a 

 fine gravel occurs, which was probably contributed by the outlet. There 

 may have been less ponding of water at this time than when water was 

 contributed by the ice sheet more directly to the basin. This subject is 

 discussed more fully in connection with the glacial lake (pp. 290, 314, 336). 



No doubt the Illinois Valley received considerable material as an out- 

 wash from this minor moraine, but as yet the deposits have not been sepa- 

 rated from those made later, and nothing is known concerning the degree of 

 coarseness of the material. 



The portion of the moraine north from the Illinois in central and 

 northern Lasalle County seems to have been no better favored for escape 

 of water than that along the border of the Illinois- Vermilion. The plain 

 west of it carries thin deposits of silt, but whether their deposition is 

 largely referable to water issuing from this moraine is not known. Pos- 

 sibly wind transportation was an important factor in the deposition. 



INTEKMORAINIC TRACTS. 

 EXTENT OR DISTRIBUTION. 



Under this topic are discussed the plains and gently undulating tracts 

 among the ridges of the Bloomington system and a plain between the inner 

 ridge of the Bloomington system and the Marseilles moraine. The inter- 

 morainic tracts are of much greater extent than the morainic, for the latter 

 are restricted to narrow belts. About 90 per cent of the area embraced 

 between the inner border of the main ridges of the Bloomington system 

 and the outer border of the Marseilles system is here classed as nonmorainic. 

 This area of about 6,000 square miles ranges in width from 25 to about 50 

 miles, being widest in central Illinois. It has a length of about 175 miles 

 between northern Kane County, Illinois, where it connects with the com- 

 posite belt of moraines, and western Benton County, Indiana, where it is 

 shut off by moraines of late Wisconsin age. 



GENERAL FEATURES. 



The portion north of the Illinois River, embracing southwestern Kane, 

 southeastern Dekalb, northwestern Kendall, northwestern Lasalle, and 



