At the mouth of Still River and for several miles north and south of
it there is a plain more than a mile broad. This plain continues
southward with a width of about one-half mile until, at Brookfield, it
is interrupted by ledges of bare rock. A little distance south of
Brookfield the valley broadens again to one-half mile, and this width
is retained with some variation as far as Danbury. Drift deposits
along the border of the valley make it appear narrower in some places
than is indicated by rock outcrops. Between Brookfield and Danbury the
narrowest place in the valley is southwest of Beaver Brook Mountain,
where the distance between the hills of rock bounding the valley is
one-fifth of a mile (fig. 6). Opposite Beaver Brook Mountain, which
presents vertical faces of granite-gneiss toward the valley, is a hill
of limestone. Ice, crowding through this narrow place in the valley,
must have torn masses of rock from the side walls, so that the valley
is now broader than in preglacial time. The constrictions in the
valley near Shelter Rock are due to the fact that the preglacial
valley, now partly buried in till, lies to the north. There are
stretches of broad floor in the valley of Beaver Brook, in the lower
valley of Umpog Creek, in the fields at the south end of Main Street
in Danbury, about Lake Kanosha, and where the Danbury Fair Grounds are
situated. In the western part of Danbury, however, and at Mill Plain
the valley is very narrow, and at the head of Sugar Hollow, the valley
lying east of Spruce Mountain, is a narrow col.
The broadest continuous area in the Still-Umpog Valley is, therefore,
in the lower six miles between Brookfield and New Milford; south of
that portion are several places where the valley is sharply
constricted; and beyond the head of the Umpog, about one and a half
miles below West Redding station (fig. 7), the Saugatuck Valley is a
very narrow gorge. On the whole, the valleys south and southwest of
Danbury are much narrower than the valley of the Still farther north.
It is evident from these observations that Still River Valley is
neither uniformly broad, nor does it increase in width toward the
south.
But if a broad valley is to be accepted as evidence of the work of a
large river, then there is too much evidence in the Still River
valley. The broad areas named above are more or less isolated
lowlands, some of them quite out of the main line of drainage, and can
not be grouped to form a continuous valley. They can not be attributed
to the Housatonic nor wholly to the work of the insignificant streams
now draining them. These broad expanses are, in fact, local peneplains
developed on areas of soluble limestone. The rock has dissolved and
the plain so produced has been made more nearly level by a coating of
peat and glacial sand. In a region of level and undisturbed strata,
such as the Ohio or Mississippi Valley, a constant relation may exist
between the size of a stream and the valley made by it; but in a
region of complicated geologic structure, such as western Connecticut,
where rocks differ widely in their resistance to erosion, the same
result is not to be expected. In this region the valleys are commonly
developed on limestone and their width is closely controlled by the
width of the belt of limestone. Even the narrow valleys in the upland
southwest of Danbury are to be accounted for by the presence of thin
lenses of limestone embedded in gneiss and schist.
The opinion of Hobbs that Still River valley is too wide to be the
work of the present stream takes into consideration only the broad
places, but when the narrow places are considered it may be said as
well that the valley is too narrow to be the work of a stream larger
than the one now occupying it. Valley width has only negative value in
interpreting the history of Still River.