184 ILLINOIS STATE ACADEMY OF SCIENCE 



water spilled over a small col in Sec. 20, T.10 S., R.l W., 

 thence into Cedar Creek, and eventually into Mississippi 

 River. The farther advance of the glacier, however, 

 eventually shut off this exit and the water found its way 

 across the divide to the south through a col just north 

 of the town of Cobden. The elevation of this col is a 

 little over 600 feet and drainage through it, and the pre- 

 viously mentioned col, may have been contemporaneous 

 for a time. The Cobden col is not a particularly large 

 col, its size suggesting that the quantity of the water 

 passing through it at any time was not large. The col 

 is cut in formations of the Chester group which are not 

 particularly resistant to erosion. The character of the 

 bedrock, therefore, would not have been a particular 

 hindrance to the enlargement of the col had it contained 

 a torrential stream. Glacial boulders have been found 

 in the valley of Cache Creek south of the col, and though 

 the presence of some of them doubtless may be assigned 

 to transportation by human agencies, it is probable that 

 most of the larger boulders were carried over the Cob- 

 den col in floating blocks of ice, and later left stranded 

 farther down-stream. 



It is a matter of interesting speculation whether with 

 a head of 200 feet of water in Drury Lake some of the 

 water of the lake may not have followed the natural 

 trend of drainage to the north through the much crev- 

 assed glacial ice, eventually to find a mode of egress into 

 the Mississippi or its tributaries; also, whether in 

 places sedimentation may not have been going on within 

 the body of the ice where it was saturated with water. 



The lake in the valley of Little Grassy Creek was not 

 as large as that in the valley of Drury Creek. Its maxi- 

 mum length was about three miles and it probably began 

 when the ice blocked the valley in Sec. 19, T.10 S., R.l E. 

 The water in this lake stood at least as high as 570 feet 

 above sea level. This is the present elevation of the 

 Water Valley col over which the water from this lake 

 found its way southward into Bradshaw Creek and even- 

 tually into Ohio River. The col is cut through a faulted 

 area in which the Kinkaid limestone of the Chester group 

 and a massive sandstone of the Pottsville formation are 



