The dominant topographic feature of western Connecticut, as may be
seen on the atlas sheets, is elongated oval hills trending north by
west to south by east, which is the direction of the axes of the folds
into which the strata were thrown at the time their metamorphism took
place. Furthermore, the direction of glacial movement in this part of
New England was almost precisely that of foliation, and scouring by
ice merely accentuated the dominant north-south trend of the valleys
and ridges. As a result, the smaller streams developed on the softer
rocks are generally parallel to each other and to the strike of the
rocks. These streams commonly bend around the ends of the hills but do
not cross them. The narrowness of the belts of soft rock makes it easy
for the drainage of the valleys to be gathered by a single lengthwise
stream. The Still and its larger tributaries conform in this way to
the structure.
On the east side of the Still-Umpog every branch, except two rivulets
1-1/4 miles south of Bethel, points in the normal direction, that is,
to the north, or downstream as the river now flows (fig. 6). The
largest eastern tributary, Beaver Brook, is in a preglacial valley now
converted into a swamp the location and size of which are due entirely
to a belt of limestone. It is not impossible that Beaver Brook may
have once flowed southward toward Bethel, but the limestone at its
mouth, which lies at least 60 feet lower than that at its head, shows
that if such were ever the case it must have been before the
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 the
direction of Still River.