314 . THE ILLINOIS GLACIAL LOBE. 



discussed on a preceding page (p. 288). The Illinois Valley, therefore, 

 appears to have been unopened along the section between the Marseilles 

 moraine and the inner moraine of the Bloomington series. 



In eastern Illinois the basin now drained by the Iroquois River north- 

 ward to the Kankakee would have been prevented from discharging in this 

 direction by the ice sheet. It is probable, as noted above, that the outlet 

 from this district was westward across the rim of the basin in northern Ford 

 County to the east fork of Vermilion River. As this rim stands somewhat 

 higher than the northern part of the basin, it may be supposed that the ice 

 sheet terminated in a shallow body of water. The only outwash found 

 along the outer borders of the moraine in this district consists of fine sand 

 and silt forming a thin coating on the surface of the till. Whether this is 

 an outwash from the ice at the time of the formation of the Marseilles 

 moraine or is of later date can scarcely be determined in the present stage 

 of investigation. Studies in western Indiana indicate that a lake may have 

 occupied this region for some time subsequent to the retreat of the ice from 

 the Marseilles moraine, and this silt-and-sand deposit may be a product of 

 the later stage of the lake. 



In eastern Livingston County there may have been a fair escape for 

 the water southward into the East Fork of Vermilion, though this is not 

 fully demonstrated. 



Reviewing the above statements, it appears that, with the possible 

 exception of the northern portion of the moraine in Kane and northern 

 Kendall counties, the ice sheet was bordered extensively by lakes, which 

 prevented a vigorous outwash. But these lakes were so shallow as to inter- 

 fere in no way with the building up of a bulky moraine. They seem also 

 to have allowed the waters escaping from the ice sheet to form the gaps 

 and indentations in the moraine, noted above. If these were formed either 

 by water escaping from the ice while it overhung the ridge, or at a later 

 date from a lake held on the east side of the ridge (the only probable agen- 

 cies yet recognized), the existence of lakes in the outer border district may 

 seem questionable. This seeming incompatibility may perhaps be explained 

 by assuming that a submarginal glacial stream had accumulated sufficient 

 hydrostatic pressure to carry a strong current into the extra-marginal lakes. 



