In order to determine whether Still River flowed southward through the
Saugatuck Valley just before the advent of the ice sheet, the borders
of Umpog Swamp and the region to the south and east were examined. It
was found that Umpog Swamp is walled in on the south by ledges of firm
crystalline limestone and that the rock-floored ravine leading
southward from the swamp, and occupied by the railroad, lies at too
high an elevation to have been the channel of a through-flowing
stream. A south-flowing Still River, and much less an ancient
Housatonic, could not have had its course through this ravine just
previous to glaciation. A course for these rivers through the short
valley which extends southeastward from Umpog Swamp is also ruled out,
because the bedrock floor of this hypothetical passageway is 20 feet
higher than the floor of the ravine through which the railroad passes.
The eastern border of Umpog Swamp is determined by a ridge of
limestone which separates the swamp from lowlying land beyond. This
ridge is continuous, except for the postglacial gorge cut by the
tributary entering from the east, and must have been in existence in
preglacial times. The entire lowland east of this limestone ridge
possesses a unity that is not in harmony with the present division of
the drainage. The streams from this hillside and those from the west
may have joined in the flat-floored valley at the head of the
Saugatuck and from there flowed into the Saugatuck system. The former
divide then lay in a line connecting the limestone rim of the swamp
with the tongue of highland which the highway crosses south of Todd
Pond (fig. 7).