Erosion of Small Basins in Indiana. — Beachler. 51 
EROSION OF SMALL BASINS IN NORTHWESTERN 
INDIANA DURING THE TIME PRECEDING 
THE PLEISTOCENE PERIOD. 
By Charles S. Beachler, Crawfordsville, Indiana. 
During the past five years in my study of the Keokuk rocks 
of northwestern Indiana, my attention has been repeatedly 
given to a high and well defined line of rock bluffs and hills 
in the central part of Montgomery <•< >unty enclosing a deep basin 
filled with drift, with an area of twenty square miles. 
The surface rocks of the county consist of Keokuk sand- 
stone underlaid by shales of the same group: the water erod- 
ing away these rocks in the center of the county left the deep 
basin which is surrounded by this high and abrupt line of 
bluffs and hills : in many places where the drift has been de- 
posited against the rocks of these old bluffs so as to hide them, 
the recent streams have cut away the drift and sought the 
low, rocky bed, again exposing the old rock wall on the out- 
side and forming a high bank of exposed glacial drift on the 
inside of the stream. The rock forming the edge of the basin be- 
tween the sources of the two small streams. South branch of 
Walnut Fork and Offield creek, is entirely hidden, as the drift 
has not been eroded. 
The material filling the basin is stratified, the lower part 
being boulder clay, which after being deposited was eroded 
and modified before it was covered with gravel and sand: at 
one place west of Crawfordsville are seen in the bottom of a 
deep gravel-pit. resting on the boulder clay, two square blocks 
of Devonian rock, probably from the vicinity of Logansport, 
which were picked up. transported and deposited by the ice 
after the boulder clay had been deposited; tin- overlying 
gravels and sands in their stratified position were then by 
the action of the water spread out. covering Over these bloeks 
of transported rocks as well as the whole of the boulder clay 
itself: then judging from the number of foreign boulders, 
some from the lake Superior region and others from the north- 
east, scattered over the surface of the material filling the 
basin, there must have been the melting of another glacier or 
of floating ice. 
