ening of the main valley. These streams, however, and others
so far as could be determined, were found to have normal profiles;
that is, their grades become increasingly flatter toward their mouths.
The streams are cutting through the till cover and are not building
alluvial cones where they join the lowland. All their features, in
fact, are characteristic of normal stream development.

Throughout the length of the valley, rock outcrops are found near the
surface, showing that the changes produced by the glacier were due to
scouring rather than to the accumulation of glacial material. Except
where stratified drift is collected locally in considerable quantity,
the glacial mantle is thin. On the other hand, it has been shown that
glacial gouging was not sufficient in amount to affect the course of
the stream. The glacier simply cleaned off the soil and rotten rock
from the surface, slackening the stream here and hastening it there,
and by blocking the course with drift it forced the river at several
places to depart slightly from its preglacial course.

The evidence shows, therefore, that if Still River has suffered
reversal, glaciation is not responsible for the change, and thus the
first two hypotheses for explaining the history of the valley are
eliminated. There remain for discussion the third and fourth
hypotheses; the former being that reversal was effected in a very
early stage in the development of the drainage, the latter that no
reversal has occurred. The choice between these two hypotheses rests
on evidence obtained in the Umpog, Croton, and other valleys of the
Danbury region. This evidence is presented in the three following
sections, after which the former courses of Still River will be
discussed.

THE STILL-SAUGATUCK DIVIDE

FEATURES OF THE UMPOG VALLEY

The valley of the Umpog, which extends from Still River to the source
of the Saugatuck near West Redding (fig. 7), is a critical area in the
study of the Still River system. It is possible that this valley once
afforded an outlet for Still River, and it has been suggested that the
Housatonic formerly followed this route to Long Island Sound. The
relation of this valley to the former drainage system of the Danbury
region demands, therefore, a careful examination of the features of
the valleys occupied by Umpog Creek and the upper waters of the
Saugatuck, and of the divide between those streams.

[Illustration: ~Fig. 7.~ Map of Umpog Swamp and vic