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,