427 



places and in other places was entirely washed away. Generally, either 

 sand or gravel overlies it. indicating that rapid flowing waters followed 

 the long period of quiet waters in which the clay was deposited. 



The next step in the history of the Flatwoods region comes with the 

 deposition of the loess material. This fine, close-textured, ash-gray-to- 

 white material composes the present surface of the region, except where the 

 long duration of swamps has built up a black soil, which in some places 

 is several feet deep over the top of the loess. The loess is somewhat 

 uncertain as to its exact time and manner of deposition, and also as to 

 the origin of the material. It was in all probability deposited not so very 

 long after the disappearance of the Illinois glacier. Its thickness varies 

 greatly in the Flatwoods region. Usually it is very thick at the margin of 

 the old lake, being as much as twenty or even thirty feet ; but in the cen- 

 tre of the region it is much thinner, at times being scarcely discernible. 

 It is thicker at the margin because it has been washed from the hills 

 adjacent. In the interior, perhaps much of it has been incorporated with 

 organic material in the making of the black soils. 



In connection with the history of Flatwoods, MeCorruicks Creek adds 

 a very fascinating chapter. After the withdrawal of the ice, the lowest 

 outlet was still the Raccoon Creek col. The region in the vicinity of the 

 headwaters of Alliston's Branch was thirty feet or more higher than the 

 Raccoon Creek col, having been built up by a possible moraine and the 

 outwash plain already described. Therefore, the waters lowered to the 

 level of the Raccoon Creek col. The water within the region was the site 

 of a shallow lake, not being any deeper tban the lowest place below the 

 Raccoon Creek col. But the waters soon fell below the level of this open- 

 ing, because of the opening of the old sinks near the margin of the region. 

 These sinks were not covered deeply by the silt and sand, and conse- 

 quently soon opened their old channels which had been filled or partly 

 filled. It is very likely that the sinks formed in the northwestern margin 

 or portion of the region in section 23, T. 10 N., R. •*! W., were the lowest 

 and were, perhaps, the first to be opened on account of the static head at 

 this place. These sinks had been draining this immediate portion of the 

 Flatwoods basin long before the advent of the Illinois glacier, and it is 

 quite likely that a thorough drainage, though underground, was already 

 established along the line of the present McCormick's Creek Gorge. It can 

 be easily seen that below the lower part of the gorge the valley bonnes 

 wiilcr. and on approaching the river it is a rilled valley. This clearly shows 



