168 J. F. NEWSOM 
The strata that form the different drainage areas and the 
watersheds between them in the southern part of the state extend 
northward under the glacial mantle for some distance beyond 
the boundary of the accompanying map (Plate 1). Therefore 
it might be expected that the preglacial relief of the country 
underlaid by those strata was similar to the present relief in the 
unglaciated area to the south, and this is found to be the case. 
The effect of the highlands (formed by groups 2 and 4) 
where they plow northward under the glacial mantle and lift it 
up, is noticeable for many miles north of the southern limit of 
the drift. These buried highlands show that the preglacial 
topography of the region thus affected was similar in general 
lines with the present topography which is almost, or entirely, 
unaffected by the drift at the southern part of the state. Well 
records show that the central drainage area, or trough, and its 
eastern rim extended as far north in preglacial time as the north 
side of Clinton county at least, while the highlands west of it 
certainly extended as far north as northern Montgomery county, 
The preglacial topography makes it seem quite probable that 
the preglacial drainage of this trough was from the eastern rim 
down the dip of the underlying limestones to the southwest, 
along lines generally parallel with those of the present streams 
further south, which are in accordance with, and are controlled 
by, the geologic structure. 
The relations of the different drainage areas and the structure 
controlling them is shown by the cross sections on the drainage 
map, Plate VI. 
It will be seen, therefore, that the drainage of southern 
Indiana may be treated in accordance with the groups of strata 
that control the topography of the region. 
Relations of the structure to the drainage -—An examination of 
the geology in its relation to the drainage shows that there are 
the three following general drainage areas :* (1) the eastern area, 
covered by rocks of the Hudson River group, and including 
«These areas cannot be regarded as basins in the proper sense of the term, for 
each area is drained by many different streams. 
