104 THE ILLINOIS GLACIAL LOBE. 



Passing northward into Owen County there is found a slight deflection 

 in Raccoon Creek, just inside the glacial boundary. Instead of following 

 its old course the creek passes across a rock point on the south, occupying 

 a gorge for about a mile. The head-water tributaries of Raccoon Creek 

 outside the glacial boundary carry terraces of silt and sand which are inter- 

 preted by Siebenthal to be the accumulations made in small glacial lakes 

 held in front of the ice sheet. 



The " Flat Woods" of eastern Owen and western Monroe counties 

 cover an area of several square miles of elevated land, immediately inside 

 the glacial boundary. The flats in this area are interrupted by hilly tracts, 

 and the entire area is above the general level of border tracts. These 

 features are thought to indicate that no large stream occupied the "Flat 

 Woods" in preglacial times. It is suggested by Siebenthal that the region 

 had a system of subterranean drainage prior to the glacial invasion, but 

 that glacial accumulations have caused a change to surface drainage. 1 The 

 flats are now drained chiefly to the north through McCormack's Creek. 

 The western portion drains westward through Ellison's Branch into White 

 River. On McCormack's Creek there is a fall about a mile from its mouth, 

 above which there is only a shallow, poorly drained valley. The main 

 work of the stream since the Glacial period has been given to the excava- 

 tion of the gorge below the fall, but no accurate estimate was made of the 

 work accomplished in cutting back to the fall. 



The effect of the ice invasion upon the course of White River has been 

 even greater than on the small eastern tributaries which enter it from the 

 unglaciated region. The preglacial drainage is so greatly concealed above 

 the north line of Greene County that it seems impracticable to determine 

 even the course of the main drainage line. The stream is now occupying a 

 preglacial valley for a few miles in southwestern Morgan County, and is 

 also in a preglacial valley throughout much of its course below Owen 

 County. But in its passage across Owen County it is opening a new val- 

 ley. It has been suggested that this stream had a subterranean passage 

 across the sink-hole region of Owen County, in which case no well-defined 

 surface channel may have been opened prior to the glacial invasion. The 

 available data seem insufficient to test the applicability of this interpretation. 



'Twenty-first Ann. Rept. Indiana Geol. Survey, 1896, pp. 301,302. 



