A tongue of the glacier is supposed to have lain in the valley of the
Umpog and gradually retreated northward after the ice had disappeared
from the uplands on either side. The ridge of intermediate height
built of limestone and schist, which extends down the middle of the
valley, was probably covered by ice for some time after the glacier
had left the highlands.
When the mountain mass extending from Pine Mountain to Town Hill west
of the Umpog Basin and the granite hills to the east terminating in
Shelter Rock are considered in their relation to the movement of the
ice, it is apparent that the valley of the Umpog must have been the
most direct and lowest outlet for glacial streams south of Danbury.
These streams built up the terraces and other deposits of stratified
drift which occupy the valley between Bethel and West Redding.
The heavy deposits of till near West Redding mark a halt in the
retreating glacier. The boulders at this point are large and numerous,
and kames and gravel ridges were formed. The deposits at the divide,
supposed to have formed a glacial dam which reversed the Umpog,[14]
are much less heavy than at points short distances north and south of
the water parting.
As the ice retreated, sand and gravel in the form of terraces
accumulated along the margin of the Umpog valley, where the drainage
was concentrated in the spaces left by the melting of the ice lobe
from the hillside. Among these deposits are the bodies of sand and
gravel which lie against the rocky hillslopes most of the way from the
Umpog-Saugatuck divide to Bethel. North of Bethel, the drainage seems
to have been gathered chiefly in streams flowing on each side of the
low ridge occupying the center of the valley; consequently the gravel
was deposited along the sides and southern end of the ridge and in the
sag which cuts across its northern end. The row of kames at the north
end of Umpog Swamp, several knolls of drift in Bethel, and the
kame-like deposits and esker north of Grassy Plain were laid down
successively as the ice retreated down the valley. During this period,
the drainage was ponded between the ice front and the Umpog-Saugatuck
divide.
Uncovering the Still-Croton valley did not give the glacial drainage
any lower outlet than the Umpog-Saugatuck divide afforded (fig. 8, B
and C.)
The heavy deposits of boulder clay forming the moraine which blocks
the Rocky River valley indicate the next halting place of the glacier.
In this period the ice margin formed an irregular northeast-southwest
line about a mile north of Danbury. The country west and south of
Danbury was thus uncovered, but the lower part of Still River valley
was either covered by the ice sheet or occupied by an ice lobe. The
drainage was, therefore, up the river valley, and being concentrated
along the valley sides resulted in the accumulation of sand and gravel
at the foot of rocky slopes. It is possible that an ice lobe extended
down the old Rocky River valley, perhaps occupying much of the country
between Beaver Brook Mountain and the high ridge west of the valley.
The streams issuing from this part of the ice front would have laid
down the eskers and kame gravels north of Danbury and the thick mantle
of drift over which Still River flows through the city. As would be
expected, this accumulation of material ponded all the north-flowing
streams--Umpog Creek, Beaver Brook, and smaller nameless ones--and at
the same time pushed Still River, at its mouth, to the southern side
of its valley. Beaver Brook valley, Umpog valley, and all the Danbury
basin must have been flooded during this period up to the height of
the "railroad divide." Within the area covered by the city, the valley
was filled up to at least 70 feet and probably much more than that
above its former level. Flowing at this higher level, the river was
thrown out of its course and here and there superimposed on hard
rock--as, for example, at Shelter Rock.
That part of the drainage coming down the valley opposite Beaver Brook
met the drainage from Still River ice lobe in the valley north of
Shelter Rock, and as a result heavy deposits of stratified drift were
laid down. The peninsula-like mass of drift beyond the river north of
Shelter Rock appears from its form to have been built up as the delta
of southward and eastward-flowing streams; probably the drainage from
the hilltops united with streams coming down the two valleys. The
lobes of stratified drift extending from the ridge may have been built
first, and later the connecting ridge of gravel which forms the top of
the hill may have accumulated as additional material was washed in,
tying together the ridges of gravel along their western ends. The
mingling in this region of stratified drift of all grades of
coarseness indicates the union in the same basin of debris gathered
from several sources.
Between Danbury and New Milford no moraine crosses either the Rocky or
the Still valley, but the abundance of till which overspreads the
whole country indicates a slowly retreating glacier well loaded with
rock debris. The mounds of stratified drift scattered along the valley
doubtless represent the deltas of streams issuing from the ice front.
The waters of Rocky River were ponded until the outlet near Jerusalem
was uncovered and the disappearance of ice from the ravine below
allowed an escape to the Housatonic. Stratified drift is present in
greatest amount along the valleys of Still River and the west fork of
Rocky River, indicating that these were the two chief lines of
drainage. The uplands are practically without stratified drift.
Along the valley of the Housatonic, glacial material is chiefly in the
form of gravel terraces; they extend from Gaylordsville to New
Milford, in some places on one side only, in others on both sides of
the river. Part of these gravel benches are kame terraces, as shown by
their rolling tops and the ravine which separates the terrace from the
hillside; others may have been made by the river cutting through the
mantle of drift which was laid down in the period of land depression
at the time of glacial retreat,[15] or they may be a combination of the
two forms. In many places by swinging in its flood plain, the river
has cut into the terraces and left steep bluffs of gravel. The valley
of Womenshenuck Brook above Merwinsville contains heavy deposits of
stratified drift, indicating that this broad valley which extends from
Kent on the Housatonic to Merwinsville was an important channel for
the water which flowed from the melting ice.
[Footnote 14: Rice, W. N. and Gregory, H. E., Manual of the Geology of
Connecticut: Conn. Geol. and Nat. Hist. Survey Bull. 6, pp. 34-35,
1906.]
[Footnote 15: Hobbs, W. H., op. cit.]
* * * * *
Transcriber's Notes:
With the following exceptions, the text presented here is that
obtained through scanned images from an original copy of the
manuscript.
Possible Typographic Errors Corrected
occuying => occupying
PLATE II A. "of" repeated
Emphasis Notation:
_text_ - italicized
=text= - bold
~text~ - small caps