north-flowing Still River had removed the limestone north of Beaver
Brook Swamp.

On the flanks of Beaver Brook Mountain are three tributaries which
enter the river against its present course. Examination of the
structure reveals, however, that these streams like those on the east
side of the river are controlled in their direction by the orientation
of the harder rock masses. The southward flowing stream four miles in
length which drains the upland west of Beaver Brook Mountain has an
abnormal direction in the upper part of its course, but on reaching
the flood plain it takes a sharp turn to the north. Above the latter
point it is in line with the streams near Beaver Brook Mountain and is
abnormal in consequence of a line of weakness in the rock.

The lowland lying west of Umpog valley, extending from Main Street in
Danbury to a point one mile beyond Bethel, affords no definite
evidence in regard to the direction of tributaries. In reconstructing
the history of this valley the chief difficulty arises from the
old-age condition of the flood plain. Drainage channels which must
once have existed have been obliterated, leaving a swampy plain which
from end to end varies less than 20 feet in elevation. It is likely
that in preglacial times the part of the valley north of Grassy Plain,
if not the entire valley, drained northward into Still River, as now
do Umpog Creek and Beaver Brook. From this outlet heavy drift deposits
near the river later cut it off. The lowland is now drained by a
stream which enters the Umpog north of Grassy Plain. Several small
streams tributary to the Umpog south of Bethel also furnish no
evidence in favor of the reversal of Still River.

West of Danbury the tributaries of Still River point upstream on one
side and downstream on the other side of the valley, in conformity
with the rock structure which is here diagonal to the limestone belt
on which the river is located. Their direction in harmony with the
trend of the rocks has, therefore, no significance in the earlier
history of the river.

From the foregoing discussion, it appears that no definite conclusions
in regard to the history of Still River can be drawn from the angle at
which tributaries enter it. The direction of the branches which enter
at an abnormal angle can be explained without assuming a reversal of
the main stream, and likewise many of the tributaries with normal
trends seem to have adopted their courses without regard to th