The mountain mass to the south and southwest of Danbury, including
Town Hill and Spruce, Moses, and Thomas mountains, is traversed by a
series of parallel gorges trending nearly north and south (fig. 2).
About midway in each valley is a col, separating north and
south-flowing streams. Two of the valleys, those between Spruce and
Moses mountains, and Thomas Mountain and Town Hill, form fairly low
and broad passes. They were examined to see whether either could have
afforded a southerly outlet for Still River.
The rock composing the mountains is granite-gneiss and schist with an
average strike of N 30 deg. W, or very nearly in line with the trend of
the valleys. The gneiss was found to be characteristic of the high
ridges and schist to be more common in the valleys. No outcrops of
limestone were found on the ridges, but at two or three localities
limestone in place was found on low ground. From the facts observed
it is evident that the stronger features of the relief are due to the
presence of bodies of resistant rock, whereas the valleys are due to
the presence of softer rock. The series of deep parallel valleys is
attributed to the presence of limestone rather than schist.
The gorge between Spruce and Moses mountains, locally called "Sugar
Hollow," narrows southward as it rises to the col, and the rock floor
is buried under till and stratified drift to depths of 25 to 50 feet.
Nevertheless it is probable that the valley was no deeper in
preglacial time than it is now. The plan of the valley with its broad
mouth to the north favored glacial scour so that the ice widened and
deepened the valley and gave it a U form. Scouring and filling are
believed to have been about equal in amount, and the present height
of the divide, about 470 feet, may be taken as the preglacial
elevation. This is 70 feet higher than the rock floor of the divide at
West Redding. The pass could not, therefore, have served as an outlet
for Still River.
The valley west of Town Hill is similar in form and origin to Sugar
Hollow. The water parting occurs in a swamp, from each end of which a
small brook flows. The height of the pass in this valley--590 feet--
precludes its use as an ancient outlet for Still River. Likewise the
valley east of Town Hill affords no evidence of occupation by a
southward through-flowing stream.