A reversal of Still River may be explained by glacial scouring which
caused the northern end of the valley to become lower than the present
divides at West Redding and Mill Plain. The evidence of such scour
should be an overdeepened, U-shaped main valley and ungraded
tributaries.

The northern part of Still River valley has not the typical U form
which results from glacial erosion. As contrasted with the U-shaped
glacial valley and the V-shaped valley of normal stream erosion, it
might be called rectangular so sharply does the flat valley floor
terminate against the steep hillsides. The floor is too smooth and
flat and the tributary valleys too closely adjusted to the variant
hardness of the rocks to be the work of such a rough instrument as the
glacier. A level so nearly perfect as that of the flood plain is the
natural result of erosion of soft rock down to a baselevel, whereas
glacial scouring tends to produce a surface with low rounded hills and
hollows.

Overdeepening would be expected, because glaciers erode without
reference to existing baselevels. That a river valley should be cut
out by ice just enough to leave it graded with respect to the main
valley would be an unusual coincidence. This is what is found where
the Still River valley joins the Housatonic, and it indicates normal
stream erosion. Also, if the limestone of the northern Still River
valley were gouged out by the glacier, the action would in all
probability have been continuous in the limestone belt to the north
of the Housatonic, and where the belt of soft rock crosses the
Housatonic the river bed would be overdeepened. Although the valley of
the Housatonic near New Milford is very flat, as is natural where a
river crosses a belt of weak rock, the outcrops are sufficiently
numerous to show that it has not been overdeepened. The limestone area
along the East Aspetuck is largely overlain by till, but here again
the presence of rock in place shows that the valley has not been
overdeepened. Moreover, limestone boulders in the southern part of
Still River valley are not as abundant as they should be under the
hypothesis that the northern part had been gouged out extensively.

That the northern part of the Still River valley was not deeply
carved by ice is shown also by the character of the tributary streams.
The three small brooks on the west side of the valley, near Beaver
Brook Mountain, were examined to see if their grades indicated an
over-deep