Malott: The ''American Bottoms'' Region 37 



in from the east, blocking them very effectively at the time 

 with ice and ice-borne material. This condition of blocked 

 drainage, which in a number of instances persisted after the 

 ablation of the ice, is everywhere in evidence along the former 

 position of the ice front. Streams in a number of cases follow 

 their pre-glacial course to near the position of the ice front 

 and then change their course to some position that gave a 

 favorable outlet to their waters previous to the melting of 

 the ice. Others persist to the White River valley, showing 

 only the effects of the temporary blocking of their courses. 

 The smaller pre-glacial streams and ravines back of the posi- 

 tion of the ice-front were for the most part obliterated by the 

 over-riding ice with its burden of till and the glacio-fluviatile 

 deposits that characterized the ablational period. Leverett^- 

 describes briefly the temporary ponding and the permanent 

 obstructions of the stream valleys heading beyond the former 

 position of the ice front. Among the most striking derange- 

 ments of drainage and ponding of pre-glacial valleys are those 

 south of the east fork of White River, namely the Patoka 

 River, Pigeon Creek, and others. North of the east fork of 

 White River, Leverett discusses the following in order from 

 south to north : Furse Creek, Richland Creek, the ''American 

 Bottoms", Raccoon Creek, and 'Tlat Woods". 



Stream Damming in the "American Bottoms'' Region. The 

 geologic map of the ''American Bottoms" shows the approxi- 

 mate area covered by the glacial invasion. It is impossible 

 to show accurately the farthest actual advance of the ice 

 itself. The criterion indicating the actual presence of the 

 glacial ice itself eri masse is boulder clay. The line on the 

 map marking the approximate position of the front of the 

 Illinois Glacial Lobe is drawn where the easternmost patches 

 of boulder clay are found. The line runs nearly due south 

 from the mouth of Beech Creek across the area, passing some- 

 what west of Park, and passing Plummers Creek about mid- 

 way between Koleen and Mineral City. 



In connection with the blocking of the drainage lines lead- 

 ing from the unglaciated area to the ice front, great quanti- 

 ties of material were carried locally by water coming from 

 the ice margin itself, sweeping the ice-contributed debris 



1- F. Leverett. The Illinois Glacial Lobe. Monograph XXXVIII, U.S. Gcolocjical Sur- 

 vey, 1898-99. Pp. 97-195. 



