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 vicinity.]
North of Bethel the Umpog occupies an open valley developed in
limestone. Knolls of limestone rise to heights of about 40 feet above
the floor of the valley and their upper surfaces are cut across the
highly, tilted beds. This truncation, together with a general
correspondence in height, suggests that these knolls, as well as the
rock terraces found between Bethel and West Redding, and the limestone
ridge which forms the divide itself, are portions of what was once a
more continuous terrace produced by stream erosion and that they
determine a former river level. The absence of accurate elevations and
the probability of glacial scour make conclusions regarding the
direction of slope of this dissected rock terrace somewhat uncertain.
As will be indicated later, however, it seems likely that these
terrace remnants mark the course of a southward flowing river that
existed in a very early stage in the development of the drainage.
South of Bethel the old Umpog valley, has lost from one-third to
one-half its width through deposits of stratified drift (Pl. II, A and
B). On the west, gravel beds lie against rock and till; on the east,
deposits of sand and coarse gravel form a bench or terrace from 500 to
700 feet broad, which after following the side of the valley for
one-half mile, crosses it diagonally and joins the western slope as a
row of rounded hills. Through this drift the present stream has cut a
narrow channel.
The narrowest part of the Umpog valley is about one mile south of
Bethel. Farther upstream the valley expands into the flat occupied by
Umpog Swamp, which presents several interesting features. The eastern,
southern, and western sides of the swamp are formed of irregular
masses of limestone and granite-gneiss 20 to 60 feet high. Near the
northwestern edge of the swamp is a terrace-like surface cut on
limestone. Its elevation is about the same as that of the beveled rock
remnants lying in Umpog valley north of Bethel.
[Illustration: ~State Geol. Nat. Hist. Survey. Bull. 30. Plate II.~
A. View up the valley of Umpog Creek. The valley dwindles in the
distance to the "railroad divide." In the middle distance is
Umpog Swamp; in the foreground the edge of the southern end of
row of Kames which points down the valley.
B. View down the valley of Umpog Creek. To the left is the edge of
limestone terrace; in the middle distance is the Catholic
cemetery situated on a terrace of stratified drift; on the right
are mounds of stratified drift; in the distance is the granite
ridge bounding the valley on the east.]
[Illustration:
~Fig. 8.~ Profiles of rivers.
A. Profile of present Still River and buried channel of
Umpog-Still River.
B. Profile of preglacial Croton-Still River.
C. Profile of preglacial Umpog-Still River.
Solid lines show the present levels.
Dotted lines show preglacial levels.]
Umpog Swamp was formerly a lake but is now nearly filled with organic
matter so that only a small remnant of the old water body remains.
Soundings have revealed no bottom at 43 feet[10] and the depth to rock
bottom is not less than 45 feet. The swamp situated one-half mile
southwest of Bethel has a depth to rock of 35 feet. In their relation
to the Still River system these two swamps may be regarded simply as
extensions of the Umpog Creek channel, but when the elevations of
their bottoms are compared with that of points to the north and south,
where the river flows on rock, it will be seen that a profile results
which is entirely out of harmony with the present profile of the
river. Thus Umpog Creek falls 40 feet at the point where it spills
over the rock ledge into the swamp, and if the 45 feet which measures
the depth of Umpog Swamp be added, the difference in level is seen to
be at least 85 feet. A similar calculation locates the bottom of the
smaller swamp near Bethel at an elevation of 340 feet above sea-level
or on the same level as the bottom of Umpog Swamp. In a straight line
2-1/4 miles north of Bethel, Still River crosses rock at a level of
350 feet, or 10 feet higher than the bottom of Umpog Swamp. At
Brookfield, 6-1/2 miles north of the mouth of the Umpog, the Still
crosses rock at 260 feet, and 4-1/2 miles farther north, it joins the
Housatonic on a rock floor 200 feet above sea-level (fig. 8, A). Such
a profile can be explained in either of two ways: glaciers gouged out
rock basins in the weak limestone, or the river in its lower part has
been forced out of its graded bed onto rock at a higher level.
Probably both causes have operated, but the latter has produced more
marked effects.
Umpog Creek has its source in a small forked stream which rises in the
granite hills east of the south end of Umpog Swamp. After passing
westward through a flat swampy area, where it is joined by the waters
from Todd Pond, the stream turns north and follows a shallow rock
gorge until Umpog Swamp is reached. The divide which separates the
present headwaters of the Umpog from those of the Saugatuck is a
till-covered swampy flat about one-quarter mile east of Todd Pond.
This arrangement of tributary streams is correctly shown in fig. 7 and
differs essentially from that shown on the Danbury atlas sheet. This
divide owes its position to the effects of glaciation. Deposits of
till and the scouring of the bed rock so modified the preglacial
surface that the upper part of the Saugatuck was cut off and made
tributary to the Umpog.
[Footnote 10: Report by T. T. Giffen, 1907.]