98 THE ILLINOIS GLACIAL LOBE. 



narrow valley and crosses the preglacial divide between Black River and the 

 South Fork of Big Creek. Thus the latter drainage basin has been greatly 

 enlarged at the expense of the former. The glacial boundary follows 

 nearly the present course of the North Fork of Big Creek below Cynthiana, 

 and the location of the new stream across the rock point near that village 

 is evidently due to the presence of the ice sheet in the lowlands to the west, 

 and the diversion across the divide between the preglacial drainage basins 

 of Black River and Big Creek is due to occupancy of the former by the 

 ice sheet. 



The Pigeon Creek drainage basin has also been enlarged at the 

 expense of Black River. Muddy Fork of Pigeon Creek lies in a lowland 

 which connects on the southwest with Black River, and this lowland appar- 

 ently received the portion of the Pigeon Creek drainage in Gibson and 

 northern Warrick counties. The location of the col was not definitely 

 worked out, though it is in all probability east of Elberfeld, in T. 4 S., 

 R. 9 W. Upon referring the question of changes of drainage in the Pigeon 

 Creek basin to Dr. George H. Ashley, of the Indiana survey, who has 

 made an examination of the portion in Warrick County outside the limits 

 of the writer's own examinations, the following reply was received: 1 



I think you are right m believing that the head waters of Pigeon Creek drained 

 to the west in preglacial times, the divide running nearly east and west across the 

 ceuter of T. 4 S. through Es. 8, 9, and 10 W. The present course of Pigeon Creek 

 through Ts. i and 5 S., E. 9 W., while not so markedly a postglacial channel as many 

 to be found, has nevertheless several of the characters of such a channel. In the 

 first place the bottoms are narrow, averaging probably less than one-half mile in 

 width from above Elberfeld to below Millersburg, or scarcely half the usual width of 

 the west-flowing head water portion. Secondly, the bluffs are more abrupt than is 

 usual for streams of this size in that region. This is especially true north of east 

 from Elberfeld, where the stream appears to have crossed an old divide. Thirdly, 

 the short tributaries on each side of the streams in the vicinity of the supposed 

 divide also sustain this view. Fourthly, reports suggest that rock is to be found 

 within a dozen feet below the stream bed in this narrow portion, but this has not as 

 yet been verified. 



The changes of drainage become still more important in passing north- 

 eastward into Pike and Dubois counties. The streams which formerly had 

 a northwestward discharge into the White River drainage have been turned 

 westward just outside the glacial boundary to form the Patoka River, as 



1 Letter written June 8, 1898. 



