LAKE KANKAKEE. 337 



been at that time no obstacle to a discharge through the Kankakee Basin to 

 the Illinois. 



The basin at the head of the Illinois apparently held a lake for a longer 

 . period than the remainder of the region under discussion. In all proba- 

 bility a ponding of waters in front of the retreating ice sheet occurred imme- 

 diately upon the withdrawal of the ice sheet from the Marseilles moraine. 

 At first the waters may have found escape through the gaps in the moraine 

 above noted, which stand at about the level of the inner border of the 

 moraine, at an altitude 640 or 650 feet above tide. The gap along the line 

 of the present Illinois River seems to have eventually drawn away the drain- 

 age from the other gaps. Evidence that lake water stood high enough to 

 discharge through these gaps is found in deposits of sand which coat the till 

 for some distance back from each of them, and in silt deposits spread more 

 widely over the basin; also in a greater smoothness of surface below the 

 level of these gaps than above that level. 



The outlet across the Marseilles moraine and districts to the west along 

 the line of the Illinois River was probably cut down very slowly, since 

 much rock has been excavated by it. Even as late as the time the Valpa- 

 raiso moraine was formed the outlet had not been cut down sufficiently to 

 drain the lake in the basin at the head of the Illinois. As already noted,, 

 terraces on the Des Plaines River, heading in the Valparaiso moraine, which 

 were formed in connection with the moraine, indicate that a lake stood in 

 this basin at the head of the Illinois while they were forming. These ter- 

 races and also beaches in the Morris Basin indicate that its level was about 

 560 feet above tide, or 60 feet above the present head of the Illinois River. 

 This stage of the lake in the Morris Basin having been thus connected 

 with the Valparaiso moraine, it is evident that the level was equally high 

 in the earlier stage, when the outwash of sand occurred on the lower 

 Iroquois and lower Kankakee. The lake level extended up the Kankakee 

 Valley about as far as Braidwood, where the sand dunes set in. It seems 

 not improbable that drainage conditions were such as to produce only a 

 sluggish flow of water in the lower Kankakee at that time, similar to the 

 present sluggish current of the upper portion of that stream. In this con- 

 nection it may be remarked that it is doubtful if any appreciable excavation 

 of the Kankakee Valley below Momence had occurred up to the time of 

 the formation of the Valparaiso moraine. It was subsequent to this that 

 HON xxxviii 22 



