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Title: Drainage Modifications and Glaciation in the Danbury Region Connecticut - State of Connecticut State Geological and Natural History - Survey Bulletin No. 30
Author: Sawyer-Harvey, Ruth
Language: English
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*** Start of this LibraryBlog Digital Book "Drainage Modifications and Glaciation in the Danbury Region Connecticut - State of Connecticut State Geological and Natural History - Survey Bulletin No. 30" ***
State of Connecticut
State Geological and Natural History Survey
Bulletin No. 30
Drainage Modifications and Glaciation
in the Danbury Region
Connecticut
By
RUTH SAWYER HARVEY, Ph. D.
HARTFORD
~Published by the State~
1920
BULLETINS
OF THE
State Geological and Natural History Survey
of Connecticut.
1. First Biennial Report of the Commissioners of the State
Geological and Natural History Survey, 1903-1904.
2. A Preliminary Report on the Protozoa of the Fresh Waters of
Connecticut: by Herbert William Conn. (Out of print. To be obtained
only in Vol. I, containing Bulletins 1-5. Price $1.50, postpaid.)
3. A Preliminary Report on the Hymeniales of Connecticut:
by Edward Albert White.
4. The Clays and Clay Industries of Connecticut: by Gerald
Francis Loughlin.
5. The Ustilagineæ, or Smuts, of Connecticut: by George
Perkins Clinton.
6. Manual of the Geology of Connecticut: by William North Rice and
Herbert Ernest Gregory. (Out of print. To be obtained only in Vol. II,
containing Bulletins 6-12. Price $2.45, postpaid.)
7. Preliminary Geological Map of Connecticut: by Herbert Ernest
Gregory and Henry Hollister Robinson.
8. Bibliography of Connecticut Geology: by Herbert Ernest Gregory.
9. Second Biennial Report of the Commissioners of the State Geological
and Natural History Survey, 1905-1906.
10. A Preliminary Report on the Algæ of the Fresh Waters of
Connecticut: by Herbert William Conn and Lucia Washburn (Hazen)
Webster.
11. The Bryophytes of Connecticut: by Alexander William Evans and
George Elwood Nichols.
12. Third Biennial Report of the Commissioners of the State Geological
and Natural History Survey, 1907-1908.
13. The Lithology of Connecticut: by Joseph Barrell and Gerald Francis
Loughlin.
14. Catalogue of the Flowering Plants and Ferns of Connecticut growing
without cultivation: by a Committee of the Connecticut Botanical
Society.
15. Second Report on the Hymeniales of Connecticut: by Edward Albert
White.
16. Guide to the Insects of Connecticut: prepared under the direction
of Wilton Everett Britton. Part I. General Introduction: by Wilton
Everett Britton. Part II. The Euplexoptera and Orthoptera of
Connecticut: by Benjamin Hovey Walden.
17. Fourth Biennial Report of the Commissioners of the State
Geological and Natural History Survey, 1909-1910.
18. Triassic Fishes of Connecticut: by Charles Rochester Eastman.
19. Echinoderms of Connecticut: by Wesley Roscoe Coe.
20. The Birds of Connecticut: by John Hall Sage and Louis Bennett
Bishop, assisted by Walter Parks Bliss.
21. Fifth Biennial Report of the Commissioners of the State Geological
and Natural History Survey, 1911-1912.
22. Guide to the Insects of Connecticut: prepared under the direction
of Wilton Everett Britton. Part III. The Hymenoptera, or Wasp-like
Insects, of Connecticut: by Henry Lorenz Viereck, with the
collaboration of Alexander Dyer MacGillivray, Charles Thomas Brues,
William Morton Wheeler, and Sievert Allen Rohwer.
23. Central Connecticut in the Geologic Past: by Joseph Barrell.
24. Triassic Life of the Connecticut Valley: by Richard Swann Lull.
25. Sixth Biennial Report of the Commissioners of the State Geological
and Natural History Survey, 1913-1914.
26. The Arthrostraca of Connecticut: by Beverly Waugh Kunkel.
27. Seventh Biennial Report of the Commissioners of the State
Geological and Natural History Survey, 1915-1916.
28. Eighth Biennial Report of the Commissioners of the State
Geological and Natural History Survey, 1917-1918.
29. The Quaternary Geology of the New Haven Region, Connecticut: by
Freeman Ward, Ph.D.
30. Drainage, Modification and Glaciation in the Danbury Region,
Connecticut: by Ruth Sawyer Harvey, Ph.D.
31. Check List of the Insects of Connecticut: by Wilton Everett
Britton, Ph.D. (In press.)
Bulletins 1, 9, 12, 17, 21, 25, 27, and 28 are merely administrative
reports containing no scientific matter. The other bulletins may be
classified as follows:
Geology: Bulletins 4, 6, 7, 8, 13, 18, 23, 24, 29, 36.
Botany: Bulletins 3, 5, 10, 11, 14, 15.
Zoölogy: Bulletins 2, 16, 19, 20, 22, 26, 31.
These bulletins are sold and otherwise distributed by the State
Librarian. Postage, when bulletins are sent by mail, is as follows:
No. 1 $0.01 No. 13 $0.08 No. 23 $0.03
3 .08 14 .16 24 .10
4 .06 15 .06 25 .02
5 .03 16 .07 26 .06
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10 .08 20 .14 30 .03
11 .07 21 .02 31
12 .02 22 .08
The prices when the bulletins are sold are as follows, postpaid:
No. 1 $0.05 No. 13 $0.40 No. 23 $0.15
3 .40 14 .75 24 .65
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7 .60 17 .05 27 .05
8 .20 18 .25 28 .05
9 .05 19 .45 29 .50
10 .35 20 .50 30 .45
11 .30 21 .05 31
12 .05 22 2.00
A part of the edition of these Bulletins have been assembled in
volumes substantially bound in cloth, plainly lettered, and sell for
the following prices, postpaid:
Volume I, containing Bulletins 1-5 $1.50
Volume II, containing Bulletins 6-12 2.45
Volume III, containing Bulletins 13-15 2.50
Volume IV, containing Bulletins 16-21 2.15
Volume V, containing Bulletin 22 2.50
It is intended to follow a liberal policy in gratuitously distributing
these publications to public libraries, colleges, and scientific
institutions, and to scientific men, teachers, and others who require
particular bulletins for their work, especially to those who are
citizens of Connecticut.
Applications or inquiries should be addressed to
~George S. Godard~,
_State Librarian_,
Hartford, Conn.
In addition to the bulletins above named, published by the State
survey, attention is called to three publications of the United States
Geological Survey prepared in co-operation with the Geological and
Natural Survey of Connecticut. These are the following:
Bulletin 484. The Granites of Connecticut: by T. Nelson Dale and
Herbert E. Gregory.
Water-Supply Paper 374. Ground Water in the Hartford, Stamford,
Salisbury, Willimantic and Saybrook Areas, Connecticut: by Herbert E.
Gregory and Arthur J. Ellis.
Water-Supply Paper 397. Ground Water in the Waterbury Area,
Connecticut: by Arthur J. Ellis, under the direction of Herbert E.
Gregory.
These papers may be obtained from the Director of the United States
Geological Survey at Washington.
CATALOGUE SLIPS.
_=Connecticut.= State geological and natural history survey._
Bulletin no. 30. Drainage Modifications and Glaciation in the Danbury
Region, Connecticut. By Ruth S. Harvey, Ph.D. Hartford, 1920.
59 pp., 5 pls., 10 fig., 25cm.
=_Harvey, Ruth Sawyer, Ph.D._=
Drainage Modification and Glaciation in the Danbury Region,
Connecticut. By Ruth S. Harvey, Ph.D. Hartford, 1920.
59 pp., 5 pls., 10 figs., 25cm.
=_Geology._=
Harvey, Ruth S. Drainage Modifications and Glaciation in
the Danbury Region, Connecticut. Hartford, 1920.
59 pp., 5 pls., 10 figs., 25^cm.
State of Connecticut
PUBLIC DOCUMENT No. 47
State Geological and Natural
History Survey
HERBERT E. GREGORY, SUPERINTENDENT
BULLETIN No. 30
~Hartford~
Printed by the State Geological and Natural History Survey
1920
State Geological and Natural History Survey
COMMISSIONERS
~Marcus H. Holcomb~, Governor of Connecticut
~Arthur Twining Hadley~, President of Yale University
~William Arnold Shanklin~, President of Wesleyan University
~Remsen Brickerhoff Ogilby~, President of Trinity College
~Charles Lewis Beach~, President of Connecticut Agricultural College
~Benjamin Tinkham Marshall~, President of Connecticut College
for Women
SUPERINTENDENT
~Herbert E. Gregory~
_Publication Approved by the Board of Control_
Drainage Modifications and Glaciation
in the Danbury Region
Connecticut
By
RUTH SAWYER HARVEY, Ph. D.
HARTFORD
Printed by the State Geological and Natural History Survey
1920
CONTENTS.
------
Page
Introduction 9
Regional relations 11
Rocky River 15
Description of the river and its valley 15
Relation of the valley to geologic structure 16
Junction of Rocky and Housatonic Rivers 18
Abnormal profile 18
Preglacial course 20
The buried channel 23
Effect of glaciation 25
The Neversink-Danbury valley 27
Still River 30
Statement of the problem 30
Evidence to be expected if Still River has been reversed 31
A valley wide throughout or broadening toward the south 32
Tributary valleys pointing upstream 34
The regional slope not in accord with the course of the Still 35
Evidence of glacial filling and degrading of the river bed 36
Glacial scouring 36
The Still-Saugatuck divide 38
Features of the Umpog valley 38
The preglacial divide 42
The Still-Croton divide 43
Introduction 43
Features of Still River valley west of Danbury 43
The Still-Croton valley 44
Glacial Lake Kanosha 45
Divides in the highlands south of Danbury 46
The ancient Still River 47
Departures of Still River from its preglacial channel 48
Suggested courses of Housatonic River 50
Glacial deposits 53
Beaver Brook Swamp 53
Deposits northeast of Danbury 54
Deposits between Beaver Brook Mountain and mouth of Still
River 54
Lakes 55
History of the glacial deposits 56
ILLUSTRATIONS.
-----------
To Face
Page
PLATE I View south on the Highland northeast of Neversink Pond 14
II A. View up the valley of Umpog Creek 40
B. View down the valley of Umpog Creek 40
III Limestone plain southwest of Danbury, in which are
situated Lake Kanosha and the Danbury Fair Grounds 44
IV A. View down the Housatonic Valley from a point one-half
mile below Stillriver Station 52
B. Part of the morainal ridge north of Danbury 52
V A. Kames in Still River valley west of Brookfield Junction 54
B. Till ridges on the western border of Still River
valley, south of Brookfield 56
Page
FIGURE 1. Present drainage of the Danbury region 13
2. Geological map of Still River valley 17
3. Profiles of present and preglacial Rocky River 19
4. Preglacial course of Rocky-Still River 21
5. Diagram showing lowest rock levels in Rocky River
valley 24
6. Course of Still River 29
7. Map of Umpog Swamp and vicinity 39
8. Profiles of rivers 41
9. Early Stage of Rocky-Still River 49
10. Five suggested outlets of Housatonic River 51
INTRODUCTION
The Danbury region of Connecticut presents many features of geographic
and geologic interest. It may be regarded as a type area, for the
history of its streams and the effects of glaciation are
representative of those of the entire State. With this idea in mind,
the field work on which this study is based included a traverse of
each stream valley and an examination of minor features, as well as a
consideration of the broader regional problems. Much detailed and
local description, therefore, is included in the text.
The matter in the present bulletin formed the main theme of a thesis
on "Drainage and Glaciation in the Central Housatonic Basin" which was
submitted in partial fulfillment of the requirements for the degree of
doctor of philosophy at Yale University.
The field work was done in 1907 and 1908 under the direction of
Professor Herbert E. Gregory. I am also indebted to the late Professor
Joseph Barrell and to Dr. Isaiah Bowman for helpful cooperation in the
preparation of the original thesis, and to Dr. H. H. Robinson for
assistance in preparing this paper for publication.
DRAINAGE MODIFICATIONS AND GLACIATION IN
THE DANBURY REGION, CONNECTICUT
--------
By Ruth S. Harvey
REGIONAL RELATIONS
The region discussed in this bulletin is situated in western
Connecticut and is approximately 8 miles wide and 18 miles long in a
north-south direction, as shown on fig. 1.[1] Throughout, the rocks
are crystalline and include gneiss, schist, and marble--the
metamorphosed equivalents of a large variety of ancient sedimentary
and igneous rocks.
For the purposes of this report, the geologic history may be said to
begin with the regional uplift which marked the close of the Mesozoic.
By that time the mountains formed by Triassic and Jurassic folding and
faulting had been worn down to a peneplain, now much dissected but
still recognizable in the accordant level of the mountain tops.
Erosion during Cretaceous time resulted in the construction of a
piedmont plain extending from an undetermined line 30 to 55 miles
north of the present Connecticut shore to a point south of Long
Island.[2] This plain is thought to have been built up of
unconsolidated sands, clays, and gravels, the débris of the Jurassic
mountains. Inland the material consisted of river-made or land
deposits; outwardly it merged into coastal plain deposits. When the
plain was uplifted, these loose gravels were swept away. In New York,
Pennsylvania, and New Jersey, however, portions of the Cretaceous
deposits are still to be found. Such deposits are present, also, on
the north shore of Long Island, and a well drilled at Barren Island on
the south shore revealed not less than 500 feet of Cretaceous
strata.[3] The existence of such thick deposits within 30 miles of the
Connecticut shore and certain peculiarities in the drainage have led
to the inference that the Cretaceous cover extended over the southern
part of Connecticut.
[Footnote 1: The streams and other topographic features of the Danbury
region are shown in detail on the Danbury and the New Milford
sheets of the United States Topographic Atlas. These sheets may be
obtained from the Director of the United States Geological Survey,
Washington, D. C.]
[Footnote 2: It was probably not less than 30 miles, for that is the
distance from the mouth of Still River, where the Housatonic enters
a gorge in the crystallines, to the sea. Fifty-five miles is the
distance to the sea from the probable old head of Housatonic River
on Wassaic Creek, near Amenia, New York.]
[Footnote 3: Veatch, A. C., Slichter, C. S., Bowman, Isaiah, Crosby,
W. O., and Horton. R. E., Underground water resources of Long
Island: U. S. G. S., PP. 44, p. 188 and fig. 24, 1906.]
A general uplift of the region brought this period of deposition to a
close. As the peneplain, probably with a mantle of Cretaceous
deposits, was raised to its present elevation, the larger streams kept
pace with the uplift by incising their valleys. The position of the
smaller streams, however, was greatly modified in the development of
the new drainage system stimulated by the uplift. The modern drainage
system may be assumed to have been at first consequent, that is,
dependent for its direction on the slope of the uplifted plain, but it
was not long before the effect of geologic structure began to make
itself felt. In the time when all the region was near baselevel, the
harder rocks had no advantage over the softer ones, and streams
wandered where they pleased. But after uplift, the streams began to
cut into the plain, and those flowing over limestone or schist
deepened, then widened their valleys much faster than could the
streams which flowed over the resistant granite and gneiss. By a
system of stream piracy and shifting, similar to that which has taken
place throughout the Newer Appalachians, the smaller streams in time
became well adjusted to the structure. They are of the class called
subsequents; on the other hand, the Housatonic, which dates at least
from the beginning of the uplift if not from the earlier period of
peneplanation, is an antecedent stream.
The complex rock surface of western Connecticut had reached a stage of
mature dissection when the region was invaded by glaciers.[4] The ice
sheet scraped off and redistributed the mantle of decayed rock which
covered the surface and in places gouged out the bedrock. The
resulting changes were of a minor order, for the main features of the
landscape and the principal drainage lines were the same in preglacial
time as they are today. It is thus seen that the history of the
smaller streams like those considered in this report involves three
factors: (1) the normal tendencies of stream development, (2) the
influence of geologic structure, and (3) the effect of glaciation.
The cover of glacial deposits is generally thin, but marked
variations exist. The fields are overspread with coarse till
containing pebbles 6 inches in diameter to huge boulders of 12 feet or
more. The abundance, size, and composition of the boulders in the till
of a given locality is well represented by the stone fences which
border fields.
[Footnote 4: This stage of glaciation is presumably Wisconsin. No
definite indication of any older glacial deposits was found.]
[Illustration: ~Fig. 1.~ Present drainage of the Danbury region.]
The regional depression which marked the close of the glacial period
slackened the speed of many rivers and caused them to deposit great
quantities of modified or assorted drift. Since glacial time, these
deposits have been dissected and formed into the terraces which are
characteristic of the rivers of the region. A form of terrace even
more common than the river-made terrace is the kame terrace found
along borders of the lowlands. Eskers in the Danbury region have not
the elongated snake-like form by which they are distinguished in some
parts of the country, notably Maine; on the contrary, they are
characteristically short and broad, many having numerous branches at
the southern end like the distributaries of an aggrading river. The
material of the eskers ranges from coarse sand to pebbles four inches
in diameter, the average size being from one to two inches. No
exposures were observed which showed a regular diminution in the
coarseness of the material toward their southern end. The clean-washed
esker gravels afford little encouragement to plant growth, and the
rain water drains away rapidly through the porous gravel.
Consequently, accumulations of stratified drift are commonly barren
places. A desert vegetation of coarse grasses, a kind of wiry moss,
and "everlastings" (_Gnaphalius decurrens_) are the principal growth.
Rattlebox (_Crotolaria sagittalis_), steeplebush (_Spiraea tomentosa_),
sweet fern (_Comptonia asplenifolia_), and on the more fertile
eskers--especially on the lower, wetter part of the slope--golden rod,
ox-eyed daisy, birch, and poplar are also present. All the eskers
observed were found to be similar: they ranged in breadth across the
top from 100 to 150 feet and the side slopes were about 20 degrees.
Only a single heavily wooded esker was found, and this ran through a
forest region.
The accumulations of stratified drift are distinguished from other
features in the landscape by their smoother and rounder outlines, by
their habit of lying unconformably on the bedrock without reference to
old erosion lines, and by a slightly different tone in the color of
the vegetation covering the water-laid material. The difference in
color, which is due to the unique elements in the flora of these
areas, may cause a hill of stratified drift in summer to present a
lighter green color than that of surrounding hills of boulder clay or
of the original rock slopes; in winter the piles of stratified drift
stand out because of the uniform light tawny red of the dried grass.
[Illustration: ~State Geol. Nat. Hist. Survey Bull. 30. Plate I.~
View south on the highland northeast of Neversink Pond. The base
of a ridge in which rock is exposed is seen at the left; a
crescent-shaped lateral moraine bordering the valley lies at the
right.]
ROCKY RIVER
DESCRIPTION OF THE RIVER AND ITS VALLEY
Rocky River begins its course as a rapid mountain brook in a rough
highland, where the mantle of till in many places is insufficient to
conceal the rock ledges (fig. 1). Near Sherman, about four miles from
its source, it enters a broad flood plain and meanders over a flat,
swampy floor which is somewhat encumbered with deposits of stratified
drift and till. Rocky hills border the valley and rise abruptly from
the lowland. The few tributaries of the river in this part of its
course are normal in direction.
About six miles below Sherman, Rocky River enters Wood Creek Swamp,
which is 5-1/2 miles long by about one mile wide and completely covers
the valley floor, extending even into tributary valleys. Within the
swamp the river is joined by Squantz Pond Brook and Wood Creek.
Tributaries to Wood Creek include Mountain Brook and the stream
passing through Barses Pond and Neversink Pond. The head of Barses
Pond is separated from the swamp only by a low ridge of till.
Neversink Pond with its inlet gorge and its long southern tributary
record significant drainage modifications, as described in the section
entitled "The Neversink-Danbury Valley."
Within and along the margin of Wood Creek Swamp, also east of Wood
Creek and at Barses Pond, are rounded, elongated ridges of till, some
of which might be called drumlins. East of Neversink Pond is the
lateral moraine shown in Pl. I. From the mouth of Wood Creek to
Jerusalem, Rocky River is a quiet stream wandering between low banks
through flat meadows, which are generally swampy almost to the foot of
the bordering hills.
Near Jerusalem bridge two small branches enter Rocky River.
Immediately north of the bridge is a level swampy area about one-half
mile in length. Where the valley closes in again, bedrock is exposed
near the stream, and beginning at a point one-half mile below (north
of) Jerusalem, Rocky River--a swift torrent choked by boulders of
great size--deserves its name.
In spite of its rapid current, however, the river is unable to move
these boulders, and for nearly three miles one can walk dry-shod on
those that lie in midstream.
At two or three places below Jerusalem, in quiet reaches above rapids,
the river has taken its first step toward making a flood plain by
building tiny beaches. One-half mile above the mouth of the river the
valley widens and on the gently rising south bank there are several
well-marked terraces about three feet in height and shaped out of
glacial material. A delta and group of small islands at the mouth of
Rocky River indicate the transporting power of the stream and the
relative weakness of the slow-moving Housatonic.
RELATIONS OF THE VALLEY TO GEOLOGIC STRUCTURE
Rocky River is classed with streams which are comformable to the rock
structure. This conclusion rests largely on the analogy between Rocky
River and other rivers of this region. The latter very commonly are
located on belts of limestone, or limestone and schist, and their
extension is along the strike. The interfluvial ridges are generally
composed of the harder rocks. The valleys of the East Aspetuck and
Womenshenuck Brook on the north side of the Housatonic, and of the
Still, the Umpog, Beaver Brook, the upper Saugatuck, and part of Rocky
River are on limestone beds (fig. 2). In the valleys between Town Hill
and Spruce Mountain (south of Danbury), two ravines northwest of
Grassy Plain (near Bethel), and the Saugatuck valley north of Umpawaug
Pond, the limestone bed is largely buried under drift, talus, and
organic deposits, but remnants which reveal the character of the
valley floors have been found. The parallelism between the courses of
these streams and that of Rocky River and the general resemblance in
the form of their valleys, flat-floored with steep-sided walls, as
well as the scattered outcrops of limestone in the valley, have led to
the inference that Rocky River, like the others, is a subsequent
stream developed on beds of weaker rock along lines of foliation.
[Illustration: ~Fig. 2.~ Geological map of Still River Valley.]
The Geological Map of Connecticut[5] shows that the valleys of Still
River, Womenshenuck Brook, Aspetuck River, and upper Rocky River are
developed on Stockbridge limestone. The lower valley of Rocky River
is, however, mapped as Becket gneiss and Thomaston granite gneiss.
Although the only outcrops along lower Rocky River are of granite, it
is believed that a belt of limestone or schist, now entirely removed,
initially determined the course of the river. The assumption of an
irregular belt of limestone in this position would account for the
series of gorges and flood plains in the vicinity of Jerusalem bridge
and for the broad drift-filled valley at the mouth of Rocky River.
These features are difficult to explain on any other basis.
[Footnote 5: Gregory, H. E., Robinson, H. H., Preliminary geological
map of Connecticut; Geol. and Nat. Hist. Survey. Bull. 7, 1907.]
JUNCTION OF ROCKY AND HOUSATONIC RIVERS
One of the distinguishing features of Rocky River is the angle at
which it joins the Housatonic (fig. 1). The tributaries of a normal
drainage system enter their master stream at acute angles, an
arrangement which involves the least expenditure of energy. Rocky
River, however, enters the Housatonic against the course of the
latter, that is, the tributary points upstream. Still River and other
southern tributaries of the Housatonic exhibit the same feature, thus
producing a barbed drainage, which indicates that some factor
interfered with the normal development of tributary streams. Barbed
drainage generally results from the reversal of direction of the
master stream[6], but it is impossible to suppose that the Housatonic
was ever reversed. As will appear, it is an antecedent master stream
crossing the crystalline rocks of western Connecticut regardless of
structure, and its course obliquely across the strike accounts for
the peculiar orientation of its southern tributaries, which are
subsequent streams whose position is determined by the nature of the
rock. For the same reason, the northern tributaries of the Housatonic
present the usual relations.
[Footnote 6: Leverett, Frank, Glacial formations and drainage features
of the Erie and Ohio basins: U. S. Geol. Survey Mon. 41, pp. 88-91,
figs. 1 and 2, 1902. See, also, the Genoa, Watkins, Penn Yan, and
Naples (New York) topographic atlas sheets.]
ABNORMAL PROFILE
The airline distance from the bend in Rocky River at Sherman to its
mouth at the Housatonic is 2-3/4 miles, but the course of the river
between these two points is 15 miles, or 5.4 times the airline
distance. This is a more extraordinary digression than that of
Tennessee River, which deserts its ancestral course to the Gulf and
flows northwest into the Ohio, multiplying the length of its course
3-1/3 times. The fall of Rocky River between Sherman and its mouth is
240 feet or 16 feet to the mile, and were the river able to take a
direct course the fall would be 87 feet to the mile. The possibility
of capture would seem to be imminent from these figures, but in
reality there is no chance of it, for an unbroken mountain ridge of
resistant rock lies between the two forks of the river. This barrier
is not likely to be crossed by any stream until the whole region has
been reduced to a peneplain.
Measured from the head of its longest branch, Rocky River is about 19
miles long and falls 950 feet. Of this fall, 710 feet occurs in the
first 4 miles and 173 feet in the last 2-1/2 miles of its course. For
the remaining distance of 12-1/2 miles, in which the river after
flowing south doubles back on itself, the fall is 67 feet, or slightly
less than 5-1/2 feet to the mile (fig. 3, A).
[Illustration: ~Fig. 3.~ Profiles of present and preglacial Rocky River.
Elevations at a, b, c and i are from U. S. G. S. map.
Elevation at d is estimated from R. E. Dakin's records.
Elevations at e, f, g and h are from R. E. Dakin's records.
The U. S. G. S. figures for the same are enclosed in parenthesis.]
In tabular form the figures, taken from the Danbury and
New Milford atlas sheets and from reports of R. E. Dakin, are
as follows:
Miles Fall in feet per mile
Source to Sherman 4 177.5
Sherman to Wood Creek 8 6.25
Wood Creek to Jerusalem 4.5 3.8
Jerusalem to mouth 2.5 69.2
Near Jerusalem, where Rocky River makes its sudden change
in grade, there is an abrupt change in the form of the valley
from broad and flat-bottomed to narrow and V-shaped. The
profile of Rocky River is thus seen to be sharply contrasted with
that of a normal stream, which is characterised throughout its
course by a decreasing slope.
PREGLACIAL COURSE
The present profile of Rocky River and the singular manner in which
the lower course of the river is doubled back on the upper course are
believed to represent changes wrought by glaciation. Before the advent
of the glacier, Rocky River probably flowed southward through the
"Neversink-Danbury Valley," to be described later, and joined the
Still at Danbury, as shown in fig. 4. The profile of the stream at
this stage in its history is shown in fig. 3, B.
At Sherman a low col separates Rocky River basin from that of the
small northward flowing stream which enters the Housatonic about a
mile below Gaylordsville. Streams by headward erosion at both ends of
the belt of limestone and schist on which they are situated have
reduced this divide to an almost imperceptible swell. The rock
outcrops in the channel show that the glacier did not produce any
change in the divide by damming, though it may have lowered it by
scouring. Assume that at one time a divide also existed on the eastern
fork of Rocky River, for example near Jerusalem. According to this
hypothesis there was, north of this latter divide, a short northward
flowing branch of the Housatonic located on a belt of weak rock,
similar to the small stream which now flows northward from Sherman, and
very like any of the half-dozen parallel streams in the rock mass
south and southwest of Danbury, all of which are subsequent streams
flowing along the strike. While these stream valleys were growing, the
southern ends of the same weak belts of rock were held by
southward-flowing streams which united in the broad limestone area now
occupied by the city of Danbury.
[Illustration: ~Fig. 4.~ Preglacial course of Rocky-Still River.
Dotted lines show present courses of the two rivers.]
The southward-flowing streams whose heads were, respectively, above
Sherman and near Jerusalem joined at the southern end of the long
ridge which includes Towner Hill and Green Mountain. Thence the stream
flowed southward along the valley now occupied by Wood Creek and
reached Still River by way of the valley which extends southward from
Neversink Pond (fig. 4).
The preglacial course of Rocky River, as above outlined, is subject to
possible modification in one minor feature, namely, the point where
the east and west forks joined. The junction may have been where
Neversink Pond is now situated, or three miles farther south than the
indicated junction near the mouth of Wood Creek. A low ridge of till
is the only barrier that at present prevents the western branch from
flowing into the head of Barses Pond and thence into Neversink Pond
(fig. 1).
As thus reconstructed the greater part of Rocky River formerly
belonged to the Still-Umpog system and formed a normal tributary in
that distant period when the Still joined the Saugatuck on its way to
the Sound (fig. 9). However, the normal condition was not lasting, for
the reversal of Still River, as later described, brought about a
complex arrangement of barbed streams (fig. 4) which remained until
modified by glacial action.
In a large stream system which has been reversed, considerable
evidence may be gathered from the angle at which tributary streams
enter. As the original direction of Rocky River in its last 2-1/2
miles is unchanged, normal tributaries should be expected; whereas
between Jerusalem and the head of the stream entering Neversink Pond
from the south, in accordance with the hypothesis that this portion of
the stream was reversed, tributaries pointing upstream might be
expected. Such little gullies as join Rocky River near its mouth are
normal in direction; between Jerusalem and the mouth of Wood Creek, a
distance of 4-1/2 miles, there are no distinct tributaries. South of
the mouth of Wood Creek are four tributaries: (1) the brook which
enters the valley from the west about one mile south of Neversink
Pond, (2) Balls Brook, which empties into Neversink Pond, and (3) two
streams on the east side--Mountain Brook and one other unnamed (fig.
1). All these, except Mountain Brook, are normal to the reconstructed
drainage. The evidence of the tributaries, though not decisive, is
thus favorable to the hypothesis of reversal.
THE BURIED CHANNEL
Figures 3 and 5 show what is known of the buried channel of Rocky
River. The only definite information as to rock levels is that derived
from the drill holes made by R. E. Dakin for the J. A. P. Crisfield
Contracting Company in connection with work on a reservoir for the
Connecticut Light and Power Company. Numerous holes were drilled at
the points indicated on fig. 5 as No. 8, D, J, No. 7+1000, and No. 7,
but only those showing the lowest rock levels need be considered. In
the following account the elevations quoted are those determined by R.
E. Dakin which differ, as shown in fig. 3, A, from those of the New
Milford atlas sheet.
Between the mouth of Wood Creek and Jerusalem bridge holes made near
the river show that the depth of the drift--chiefly sand, gravel, and
clay--varies from 45 to 140 feet. The greatest thickness of drift,
consisting of humus, quicksand and clay, is 140 feet at a point 20
feet from the east bank of Rocky River and about 1-3/4 miles north of
the mouth of Wood Creek (fig. 5, D). Although some allowance should be
made for glacial scouring, the rock level at this point, 244 feet, is
so much lower than any other record obtained between this point and
Danbury that one is obliged to assume a buried channel with a level at
Danbury at least 75 feet below the rock level found in the lowest well
record.[7] It is probable that this well is not situated where the
rock is lowest, that is, it may be on one side of the old Still River
channel.
[Footnote 7: Well of J. Hornig, rear of Bottling Works, near foot of
Tower Place, 35 ft. to rock, indicated at _a_, fig. 5. The well of
Bartley & Clancey, 94 White Street, 70 ft. to rock, is also
indicated at _b_, fig. 5.]
The level obtained at No. 8 is from a hole drilled within 50 feet of
the river. The drill struck rock at an elevation of 316 feet after
passing through 69 feet of quicksand, gravel, and till. This is
clearly not within the channel as it is quite impossible to reconcile
the figure with that at D, less than a mile distant.
South of Jerusalem bridge at J, 150 feet from the river, a hole was
bored through 95 feet of clay, sand, and gravel before striking rock
at an elevation of 298 feet.
[Illustration: ~Fig. 5.~ Rocky River Valley. Diagram indicating lowest
rock levels which have been discovered by drilling.]
At the point marked No. 7+1000, about 1-1/4 miles from the mouth of
Rocky River, the evidence derived from 8 drill holes, bored at
distances ranging from 200 to 550 feet from the right bank, shows the
drift cover to be from 48 to 72 feet in thickness. At 200 feet from
the river the drill passed through 72 feet of sand, clay, and gravel
before striking rock at 303 feet above sea-level.
At No. 7, about one mile from the mouth of Rocky River, a hole drilled
415 feet from the right bank showed 58 feet of drift, consisting of
clay, sand, gravel, and boulders. The drill reached rock at 342 feet,
which is the figure given by R. E. Dakin for the elevation of the
river at this point. Drill holes made, respectively, at 50 and 60 feet
to the right of this one showed a drift cover of 61 feet, so that the
underlying rock rises only 4 feet in a distance of 475 feet to the
east of the river.
The foregoing evidence, showing a rock level at D 98 feet lower than
that at No. 7, leaves no doubt that the preglacial course of Rocky
River was to the south from No. 7, and there is nothing in the
topography between Jerusalem and Danbury to make improbable the
existence of a buried channel.
EFFECT OF GLACIATION
The preglacial history of Rocky River as outlined assumes that before
the glacier covered this part of Connecticut the present lower course
of Rocky River was separated from the rest of the system by a divide
situated somewhere between the present mouth of the river and the
mouth of Wood Creek. It remains to be shown by what process Rocky
River was cut off from its southern outlet into Still River and forced
up its eastern branch and over the col into a tributary of the
Housatonic. Though the preglacial course of Rocky River appears to be
more natural than the present one, it is really a longer course to the
Housatonic; the older route being 32 miles, whereas the present course
is 19 miles. This fact explains, in part, why the glacier had little
difficulty in altering the preglacial drainage, and how the change so
effected became permanent. Eccentric as the resulting system of
drainage is, it would have been still more so had Rocky River when
ponded overflowed at the head of its western instead of its eastern
fork, taken its way past Sherman into the Housatonic near
Gaylordsville, and discharging at this point lost the advantage of the
fall of the Housatonic between Gaylordsville and Boardman.
In glaciated regions an area of swamp land may be taken as an
indication of interference by the glacier with the natural run-off.
The swamp in which Wood Creek joins the upper fork of Rocky River
(fig. 1), was formerly a lake due to a dam built across the lower end
of a river valley. Although the ponded water extended only a short
distance up the steeper side valleys, it extended several miles up the
main stream. The whole area of this glacial lake, except two small
ponds and the narrow channels through which the river now flows, has
been converted into a peat-filled bog having a depth of from 8 to 45
feet.[8]
At the termination of the swampy area on the eastern branch of Rocky
River no indication is found of a dam such as would be required for so
extensive a ponding of the waters. Here the valley is very narrow, and
though the river bed is encumbered with heavy boulders, rock outcrops
are so numerous as to preclude the idea of a drift cover raising the
water level. This is just the condition to be expected if Rocky River
reached its present outlet by overtopping a low col at the head of its
former eastern branch.
The southern end of the Neversink Pond valley is the only other place
whose level is so low that drift deposits could have interfered with
the Rocky River drainage. The moraine at the head of this valley,
crossing the country some two miles north of the city of Danbury and
binding together two prominent north-and-south ridges, was evidently
the barrier which choked the Rocky River valley near its mouth and
turned back the preglacial river.
When Rocky River was thus ponded its lowest outlet was found to be at
the head of its eastern fork. Here the waters spilled over the old
divide and took possession of the channel of a small stream draining
into the Housatonic. Accordingly Rocky River should be found cutting
its bed where it crosses the former divide. It seems reasonable to
regard the gorge half-way between Jerusalem bridge and Housatonic
River as approximately the position of the preglacial divide and to
consider the small flat area to the north of Jerusalem bridge as a
flood plain on softer rock, worn down as low as the outcrops of more
resistant rock occurring farther down the valley will permit. The
reversal of the river may account for the sudden transition from a
flat-bottomed valley to a rocky gorge; and for the abrupt change in
the profile, bringing the steepest part of the river near its mouth.
The increased volume of water flowing through the channel since
glacial time has plainly cut down the bed of the ravine between
Jerusalem and the river's mouth, but the channel is still far from
being graded.
[Footnote 8: Report of soundings made in 1907 by T. T. Giffen.]
THE NEVERSINK-DANBURY VALLEY.
Between Neversink Pond and Danbury extends a deep rock valley, in
places filled with drift. As has been shown, this valley was probably
occupied in preglacial time by Rocky River, which then flowed
southward. At its southern end is Still River, which flows through
Danbury from west to east.
The most important tributary of the Still rises northwest of the city,
just beyond the New York-Connecticut boundary line, and has two forks.
The northern fork, which drains East Lake, Padanaram Reservoir, and
Margerie Pond, flows along the northeast side of Clapboard Ridge. The
southern fork has two branches; the northern one includes the
reservoirs of Upper Kohanza and Lake Kohanza, while the upper waters
of the southern branch have been recently dammed to form an extensive
reservoir. On approaching the city, the northernmost fork (draining
East Lake) turns sharply out of its southeast course and flows in a
direction a little east of north. At the end of Clapboard Ridge, the
stream makes a detour around a knoll of coarse stratified drift. From
this turn until it joins Still River, a distance of about a mile, the
stream occupies a broad and partly swampy valley.
At the cemetery in this valley (fig. 1, C) are two eskers of symmetric
form, each a few hundred yards in length and trending nearly parallel
with the valley axis. East of the valley, and about 1-1/2 miles north
of the cemetery, is a broad, flat-topped ridge of till with rock
exposed at the ends, forming a barrier which doubtless existed in
preglacial time. West of the valley is a hill with rock foundation
rounded out on the northeast side by a mass of drift. The preglacial
course of Rocky River was between the outcrops at these two
localities.
Northwest of the cemetery for one and a half miles the uneven surface
is formed of till and small patches of stratified drift. In a swamp
near the north end of the cemetery is a curved esker with lobes
extending south and southwest. One mile north of this swamp is an area
of excessively coarse till containing boulders which range in diameter
from 6 to 10 feet and forming a low ridge separating two ravines, in
which head streams flowing in opposite directions. The area of coarse
till is bounded on the north by a long sinuous esker of coarse gravel
terminating in a flat fan, which is superposed on a field of fine
till. Associated with the esker is an interesting group of kames and
kettleholes, the largest kettlehole being distinguished by distinct
plant zones banding the sides of the depression.
North of the area of boulders, eskers, and kames just described lies a
swamp whose surface is 30 to 40 feet below the upper level of the kame
gravels. Soundings made by T. T. Giffen revealed the presence of 36
feet of peat and 2 feet of silt overlying firm sand, so that 70 feet
is the minimum estimate for the difference in level between the
surface of the gravels and the floor of the swamp.
Below the rocky cliffs which line the valley sides are boulders
brought by the ice from near-by ledges, and about one-half mile above
the head of the swamp are remnants of a terrace standing 20 to 30 feet
above the level of the stream. Although the terrace appears to consist
of till, it may conceal a rock floor which was cut by a former stream.
As the valley is followed toward Neversink Pond, the various features
of a till-coated, rock-floored valley are seen.
[Illustration: ~Fig. 6.~ Course of Still River. Dotted lines show the
preglacial channels.]
STILL RIVER
STATEMENT OF THE PROBLEM
Still River presents several unusual features, as shown in fig. 6.
Tributaries from the west and south unite at Danbury to form a stream
flowing northward opposite to the regional land slope. Near its
junction with the Housatonic, the river flows northward, whereas its
master stream half a mile distant flows southward. The lower valley of
the river is broad and flat and apparently much out of proportion to
the present stream; it is, indeed, comformable in size and direction
with the valley of the Housatonic above the mouth of the Still. The
Housatonic, however, instead of choosing the broad lowland in the
limestone formation, spread invitingly before it, turns aside and
flows through a narrow gorge cut in resistant gneiss, schist, and
igneous intrusives. The headwaters of the Still mingle with those of
the Croton system, and its chief southern branch, the Umpog, is
interlaced with the sources of the Saugatuck on a divide marked by
glacial drift and swamps. The explanation of these features involves
not only the history of the Still River system, but also that of the
Housatonic.
In explanation of the present unusual arrangement of streams in
the Still River system, four hypotheses may be considered:
I. Still River valley is the ancient bed of the Housatonic from which
that river has been diverted through reversal caused by a glacial dam.
II. The Housatonic has always had its present southeasterly course,
but the Still, heading at some point in its valley north of Danbury,
flowed initially southward through one of four possible outlets. The
latter stream was later reversed by a glacial dam at the southern end,
or by glacial scouring at the northern end of its valley which removed
the divide between its headwaters and the Housatonic.
III. The Housatonic has always held its present southeasterly course,
and the Still initially flowed southward, as stated above. Reversal in
this case, however, occurred in a very early stage in the development
of the drainage, as the result of the capture of the headwaters of the
Still by a small tributary of the Housatonic.
IV. The Housatonic has always held its present southeasterly course,
but the Still has developed from the beginning as a subsequent stream
in the direction in which it now flows.
The first hypothesis, that the Still is the ancient channel of the
Housatonic, has been advocated by Professor Hobbs, who has stated:
"That the valley of the Still was formerly occupied by a large
stream is probable from its wide valley area.... The former
discharge of the waters of the Housatonic through the Still into
the Croton system, on the one hand, or into the Saugatuck on the
other, would require the assumption of extremely slight changes
only in the rock channels which now connect them.... To turn the
river (the Housatonic) from its course along the limestone
valley some obstruction or differential uplift within the river
basin may have been responsible. The former seems to be the more
probable explanation in view of the large accumulations of drift
material in the area south and west of Bethel and Danbury."
"The structural valleys believed to be present in the
crystalline rocks of the uplands due to post-Newark deformation
may well have directed the course of the Housatonic after it had
once deserted the limestone ... The deep gorge of the Housatonic
through which the river enters the uplands not only crosses the
first high ridge of gneiss in the rectilinear direction of one
of the fault series, but its precipitous walls show the presence
of minor planes of dislocation, along which the bottom of the
valley appears to have been depressed."[9]
The hypothesis proposed by Professor Hobbs and also the second and
third hypotheses here given involve the supposition of reversal of
drainage, and their validity rests on the probability that the stream
now occupying Still River valley formerly flowed southward. The first
and second hypotheses will be considered in the following section.
[Footnote 9: Hobbs, W. H., Still rivers of western Connecticut: Bull.
Geol. Soc. Am., vol. 13, pp. 17-26, 1901.]
EVIDENCE TO BE EXPECTED IF STILL RIVER HAS BEEN REVERSED
If Still River occupies the valley of a reversed stream, the following
physiographic features should be expected:
1. A valley with a continuous width corresponding to the size of the
ancient stream, or a valley comparatively narrow at the north and
broadening toward the south.
2. Tributary valleys pointing upstream with respect to the present
river.
3. The regional slope not in accord with the present course of the
river.
4. Extensive glacial filling and ponded waters in the region of the
present sources of Still River.
5. Strong glacial scouring at the northern end in default of a glacial
dam at the southern end of the valley, or to assist a dam in its work
of reversing the river. The evidence of glacial erosion would be a
U-shaped valley, overdeepening of the main valley, and tributaries
ungraded with respect to the main stream.
1. A VALLEY WIDE THROUGHOUT OR BROADENING TOWARD THE SOUTH
At the mouth of Still River and for several miles north and south of
it there is a plain more than a mile broad. This plain continues
southward with a width of about one-half mile until, at Brookfield, it
is interrupted by ledges of bare rock. A little distance south of
Brookfield the valley broadens again to one-half mile, and this width
is retained with some variation as far as Danbury. Drift deposits
along the border of the valley make it appear narrower in some places
than is indicated by rock outcrops. Between Brookfield and Danbury the
narrowest place in the valley is southwest of Beaver Brook Mountain,
where the distance between the hills of rock bounding the valley is
one-fifth of a mile (fig. 6). Opposite Beaver Brook Mountain, which
presents vertical faces of granite-gneiss toward the valley, is a hill
of limestone. Ice, crowding through this narrow place in the valley,
must have torn masses of rock from the side walls, so that the valley
is now broader than in preglacial time. The constrictions in the
valley near Shelter Rock are due to the fact that the preglacial
valley, now partly buried in till, lies to the north. There are
stretches of broad floor in the valley of Beaver Brook, in the lower
valley of Umpog Creek, in the fields at the south end of Main Street
in Danbury, about Lake Kanosha, and where the Danbury Fair Grounds are
situated. In the western part of Danbury, however, and at Mill Plain
the valley is very narrow, and at the head of Sugar Hollow, the valley
lying east of Spruce Mountain, is a narrow col.
The broadest continuous area in the Still-Umpog Valley is, therefore,
in the lower six miles between Brookfield and New Milford; south of
that portion are several places where the valley is sharply
constricted; and beyond the head of the Umpog, about one and a half
miles below West Redding station (fig. 7), the Saugatuck Valley is a
very narrow gorge. On the whole, the valleys south and southwest of
Danbury are much narrower than the valley of the Still farther north.
It is evident from these observations that Still River Valley is
neither uniformly broad, nor does it increase in width toward the
south.
But if a broad valley is to be accepted as evidence of the work of a
large river, then there is too much evidence in the Still River
valley. The broad areas named above are more or less isolated
lowlands, some of them quite out of the main line of drainage, and can
not be grouped to form a continuous valley. They can not be attributed
to the Housatonic nor wholly to the work of the insignificant streams
now draining them. These broad expanses are, in fact, local peneplains
developed on areas of soluble limestone. The rock has dissolved and
the plain so produced has been made more nearly level by a coating of
peat and glacial sand. In a region of level and undisturbed strata,
such as the Ohio or Mississippi Valley, a constant relation may exist
between the size of a stream and the valley made by it; but in a
region of complicated geologic structure, such as western Connecticut,
where rocks differ widely in their resistance to erosion, the same
result is not to be expected. In this region the valleys are commonly
developed on limestone and their width is closely controlled by the
width of the belt of limestone. Even the narrow valleys in the upland
southwest of Danbury are to be accounted for by the presence of thin
lenses of limestone embedded in gneiss and schist.
The opinion of Hobbs that Still River valley is too wide to be the
work of the present stream takes into consideration only the broad
places, but when the narrow places are considered it may be said as
well that the valley is too narrow to be the work of a stream larger
than the one now occupying it. Valley width has only negative value in
interpreting the history of Still River.
2. TRIBUTARY VALLEYS POINTING UPSTREAM
The dominant topographic feature of western Connecticut, as may be
seen on the atlas sheets, is elongated oval hills trending north by
west to south by east, which is the direction of the axes of the folds
into which the strata were thrown at the time their metamorphism took
place. Furthermore, the direction of glacial movement in this part of
New England was almost precisely that of foliation, and scouring by
ice merely accentuated the dominant north-south trend of the valleys
and ridges. As a result, the smaller streams developed on the softer
rocks are generally parallel to each other and to the strike of the
rocks. These streams commonly bend around the ends of the hills but do
not cross them. The narrowness of the belts of soft rock makes it easy
for the drainage of the valleys to be gathered by a single lengthwise
stream. The Still and its larger tributaries conform in this way to
the structure.
On the east side of the Still-Umpog every branch, except two rivulets
1-1/4 miles south of Bethel, points in the normal direction, that is,
to the north, or downstream as the river now flows (fig. 6). The
largest eastern tributary, Beaver Brook, is in a preglacial valley now
converted into a swamp the location and size of which are due entirely
to a belt of limestone. It is not impossible that Beaver Brook may
have once flowed southward toward Bethel, but the limestone at its
mouth, which lies at least 60 feet lower than that at its head, shows
that if such were ever the case it must have been before the
north-flowing Still River had removed the limestone north of Beaver
Brook Swamp.
On the flanks of Beaver Brook Mountain are three tributaries which
enter the river against its present course. Examination of the
structure reveals, however, that these streams like those on the east
side of the river are controlled in their direction by the orientation
of the harder rock masses. The southward flowing stream four miles in
length which drains the upland west of Beaver Brook Mountain has an
abnormal direction in the upper part of its course, but on reaching
the flood plain it takes a sharp turn to the north. Above the latter
point it is in line with the streams near Beaver Brook Mountain and is
abnormal in consequence of a line of weakness in the rock.
The lowland lying west of Umpog valley, extending from Main Street in
Danbury to a point one mile beyond Bethel, affords no definite
evidence in regard to the direction of tributaries. In reconstructing
the history of this valley the chief difficulty arises from the
old-age condition of the flood plain. Drainage channels which must
once have existed have been obliterated, leaving a swampy plain which
from end to end varies less than 20 feet in elevation. It is likely
that in preglacial times the part of the valley north of Grassy Plain,
if not the entire valley, drained northward into Still River, as now
do Umpog Creek and Beaver Brook. From this outlet heavy drift deposits
near the river later cut it off. The lowland is now drained by a
stream which enters the Umpog north of Grassy Plain. Several small
streams tributary to the Umpog south of Bethel also furnish no
evidence in favor of the reversal of Still River.
West of Danbury the tributaries of Still River point upstream on one
side and downstream on the other side of the valley, in conformity
with the rock structure which is here diagonal to the limestone belt
on which the river is located. Their direction in harmony with the
trend of the rocks has, therefore, no significance in the earlier
history of the river.
From the foregoing discussion, it appears that no definite conclusions
in regard to the history of Still River can be drawn from the angle at
which tributaries enter it. The direction of the branches which enter
at an abnormal angle can be explained without assuming a reversal of
the main stream, and likewise many of the tributaries with normal
trends seem to have adopted their courses without regard to the
direction of Still River.
3. REGIONAL SLOPE NOT IN ACCORD WITH COURSE OF THE STILL
Although the regional slope of western Connecticut as a whole is
contrary to that of Still River, there is no marked lowering of the
hill summits between the source of the river and its mouth. As
branches on the south side of the Housatonic are naturally to be
expected, there is nothing unusual in the Still flowing in opposition
to the regional slope, except that it flows toward the north instead
of the northeast.
4. EVIDENCE OF GLACIAL FILLING AND DEGRADING OF THE RIVER BED
Hobbs has suggested that the waters of the Housatonic may have been
ponded at a point near West Redding until they rose high enough to
overflow into the "fault gorge" below Still River Station, thus giving
the streams of the Danbury region an outlet to the Sound by this
route. This hypothesis calls for a glacial dam which has not been
found. It is true there are glacial deposits in the Umpog valley south
of Bethel. The Umpog flows as it does, however, not because of a
glacial "dam" but in spite of it. The river heads on rock beyond and
above the glacial deposits and picks its way through them (fig. 7).
Drift forms the divide at the western end of Still River valley beyond
Mill Plain, but the ponded water which it caused did not extend as far
as Danbury (see discussion of Still-Croton valley). The Sugar Hollow
pass is also filled with a heavy mantle of drift, but the valley is
both too high and too narrow at the col to have been the outlet of the
Housatonic.
It might be assumed that just previous to the advent of the ice sheet
Still River headed south of its present mouth and flowed southward. In
this case the Still, when reversed, should have overflowed at the
lowest point on the divide between it and the Housatonic. It should
have deepened its channel over the former divide, and the result would
have been a gorge if the divide were high, or at least some evidence
of river cutting even if the divide were low. On the contrary, Still
River joins the Housatonic in a low, broad, and poorly drained plain.
The existing relief is due to the uneven distribution of drift. The
river is now cutting a gorge at Lanesville, but the appearance of the
valley to the west indicates that glacial deposits forced the river
out of its former bed (fig. 6) and that no barrier lay between the
preglacial Still River valley and the Housatonic Valley.
5. GLACIAL SCOURING
A reversal of Still River may be explained by glacial scouring which
caused the northern end of the valley to become lower than the present
divides at West Redding and Mill Plain. The evidence of such scour
should be an overdeepened, U-shaped main valley and ungraded
tributaries.
The northern part of Still River valley has not the typical U form
which results from glacial erosion. As contrasted with the U-shaped
glacial valley and the V-shaped valley of normal stream erosion, it
might be called rectangular so sharply does the flat valley floor
terminate against the steep hillsides. The floor is too smooth and
flat and the tributary valleys too closely adjusted to the variant
hardness of the rocks to be the work of such a rough instrument as the
glacier. A level so nearly perfect as that of the flood plain is the
natural result of erosion of soft rock down to a baselevel, whereas
glacial scouring tends to produce a surface with low rounded hills and
hollows.
Overdeepening would be expected, because glaciers erode without
reference to existing baselevels. That a river valley should be cut
out by ice just enough to leave it graded with respect to the main
valley would be an unusual coincidence. This is what is found where
the Still River valley joins the Housatonic, and it indicates normal
stream erosion. Also, if the limestone of the northern Still River
valley were gouged out by the glacier, the action would in all
probability have been continuous in the limestone belt to the north
of the Housatonic, and where the belt of soft rock crosses the
Housatonic the river bed would be overdeepened. Although the valley of
the Housatonic near New Milford is very flat, as is natural where a
river crosses a belt of weak rock, the outcrops are sufficiently
numerous to show that it has not been overdeepened. The limestone area
along the East Aspetuck is largely overlain by till, but here again
the presence of rock in place shows that the valley has not been
overdeepened. Moreover, limestone boulders in the southern part of
Still River valley are not as abundant as they should be under the
hypothesis that the northern part had been gouged out extensively.
That the northern part of the Still River valley was not deeply
carved by ice is shown also by the character of the tributary streams.
The three small brooks on the west side of the valley, near Beaver
Brook Mountain, were examined to see if their grades indicated an
over-deepening 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 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.]
THE PREGLACIAL DIVIDE
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).
THE STILL-CROTON DIVIDE
INTRODUCTION
The deep valley extending from the Danbury Fair Grounds to the East
Branch Reservoir in the Croton River system, has given rise to the
suggestion that the course of the Housatonic formerly may have been
along the line of Still and Croton rivers and thence to the
Hudson.[11] From the evidence of the topographic map alone, this
hypothesis appears improbable. The trend of the larger streams in
western Connecticut is to the south and southeast; a southwesterly
course, therefore, would be out of harmony with the prevailing
direction of drainage. Also, the distance from the present mouth of
Still River to tidewater by the Still-Croton route is longer than
the present route by way of the Housatonic.
[Footnote 11: Hobbs, W. H., Still rivers of western Connecticut: Bull.
Geol. Soc. Am., vol. 13, p. 25, 1901.]
FEATURES OF STILL RIVER VALLEY WEST OF DANBURY
From Danbury to its source Still River occupies a valley whose
features are significant in the history of the drainage. Between
Danbury and the Fair Grounds (fig. 1) the valley is a V-shaped ravine
1-1/2 miles long, well proportioned to the small stream now occupying
it but entirely too narrow for the channel of a large river. Along the
valley are outcrops of schist, and granite rock is present on both
sides of the valley for a distance of about one-quarter mile. Part of
the valley is a mere cleft cut in the rock and is unglaciated. At the
Danbury Fair Grounds the valley opens out into a marshy plain, through
which the river meanders and receives two tributaries from the south.
The plain, which extends beyond Lake Kanosha on the west, has a
generally level surface but is diversified in places by mounds of
stratified drift.
Near the railroad a rock outcrop was found which gives a clue to the
nature of the broad lowland. The rock consists mainly of schist, but
on the side next the valley there is a facing of rotten limestone.
This plain, like all the others in this region, is a local peneplain
developed on soluble limestone. A better example could not be found to
prove the fallacy of the saying that "a broad valley proves the
existence of a large river." The plain is simply a local expansion of
a valley which on each side is much narrower. No other river than the
one flowing through it can have been responsible for the erosion, for
the plain is enclosed by hills of gneiss and schist (Pl. III).
At Mill Plain the valley is crowded by ragged rock outcrops which jut
into the lowland. Here the river occupies a ravine cut in till near
the north side of the valley. West of Mill Plain station the valley is
encumbered with ridges of stratified drift, interspersed with heavy
accumulations of till. Near Andrew Pond the true width of the
valley--one-eighth mile--is shown by rock outcrops on both the north
and south slopes. The valley at this point gives no indication of
narrowing toward the headwaters; in fact, it becomes broader toward
the west.
Between Andrew Pond and Haines' Pond is the divide which separates the
waters of the Still system from those of the Croton. It consists of a
jumbled mass of morainal hills, seemingly of boulder clay, that rise
from 50 to 60 feet above the level of the ponds. The divide is thus
merely a local obstruction in what was formerly a through drainage
channel.
THE STILL-CROTON VALLEY
It is evident that before the advent of the glacier a stream must have
flowed through the Still-Croton valley past the present divide in
order to have excavated the rock valley there found. The Housatonic
could not have flowed west through this valley if it was as narrow and
shallow as is indicated by known rock outcrops; the river could have
flowed through it only in a deep narrow gorge which was later buried
under drift, but the evidence at hand does not support this view.
[Illustration: ~State Geol. Nat. Hist. Survey Bull. 30. Plate III.~
Limestone Plain southwest of Danbury, in which are situated the
Danbury Fair Grounds and Lake Kanosha.]
It is most probable that this valley was made by the preglacial
Croton River. This explanation demands no change in the direction of
Still and Croton Rivers but calls for a divide at some point east of
the present one. From a divide between the Fair Grounds and Danbury, a
small stream may be supposed to have flowed toward the east, joining
the larger northern branch of the Still at a point near the middle of
the city of Danbury. The stream flowing westward from this divide
formed the headwaters of one branch of the Croton system.
The presence of till in a ravine can be used as a criterion for
locating the site of a former divide, for where till is present in
the bed of a stream the channel is of preglacial date. Where the river
crosses a divide it should be cutting through rock, though till may be
present on the valley slopes. Judged by this test, the old divide was
situated either just east of the Fair Grounds plain or at the east end
of the ravine described in the preceding topic. Of these two positions
the one near the Fair Grounds seems the more likely (fig. 1), for at
this place the river has excavated a recent channel with steep sides
in gneissoid rock. The absence of the limestone at this point may be
sufficient in itself to explain the location of the divide.
Exact measurements of the drift in the upper Still valley are needed
in order to establish this hypothesis completely and to plot the old
channel, but the position of the rock floor of the former channel
extending westward from the Fair Grounds may be fixed approximately.
The rock at the assumed divide now stands at 420 feet above sea-level
and it is reasonable to assume that ten feet has been removed by
glacial scouring and postglacial erosion, making the original
elevation 430 feet. The present divide between Andrew Pond and Haines'
Pond has an elevation of 460, but the bedrock at this place is buried
under 60 feet of drift, so that the valley floor lies at 400 feet.
According to these estimates the stream which headed east of the Fair
Grounds had a fall of 30 feet before reaching the site of the present
Haines' Pond (fig. 8, B).
GLACIAL LAKE KANOSHA
When the Croton Branch was beheaded by drift choking up its valley
west of Andrew Pond, the ponded waters rose to a height of from 20 to
30 feet and then overflowed the basin on the side toward Danbury. The
outlet was established across the old divide, and as the gorge by
which the water escaped was cut down, the level of the ponded waters
was lowered. At the same time, also, the lake was filled by debris
washed into it from the surrounding slopes. Thus the present flat
plain was formed and the old valley floor, a local peneplain developed
on the limestone, was hidden.
DIVIDES IN THE HIGHLANDS SOUTH OF DANBURY
The mountain mass to the south and southwest of Danbury, including
Town Hill and Spruce, Moses, and Thomas mountains, is traversed by a
series of parallel gorges trending nearly north and south (fig. 2).
About midway in each valley is a col, separating north and
south-flowing streams. Two of the valleys, those between Spruce and
Moses mountains, and Thomas Mountain and Town Hill, form fairly low
and broad passes. They were examined to see whether either could have
afforded a southerly outlet for Still River.
The rock composing the mountains is granite-gneiss and schist with an
average strike of N 30° W, or very nearly in line with the trend of
the valleys. The gneiss was found to be characteristic of the high
ridges and schist to be more common in the valleys. No outcrops of
limestone were found on the ridges, but at two or three localities
limestone in place was found on low ground. From the facts observed
it is evident that the stronger features of the relief are due to the
presence of bodies of resistant rock, whereas the valleys are due to
the presence of softer rock. The series of deep parallel valleys is
attributed to the presence of limestone rather than schist.
The gorge between Spruce and Moses mountains, locally called "Sugar
Hollow," narrows southward as it rises to the col, and the rock floor
is buried under till and stratified drift to depths of 25 to 50 feet.
Nevertheless it is probable that the valley was no deeper in
preglacial time than it is now. The plan of the valley with its broad
mouth to the north favored glacial scour so that the ice widened and
deepened the valley and gave it a U form. Scouring and filling are
believed to have been about equal in amount, and the present height
of the divide, about 470 feet, may be taken as the preglacial
elevation. This is 70 feet higher than the rock floor of the divide at
West Redding. The pass could not, therefore, have served as an outlet
for Still River.
The valley west of Town Hill is similar in form and origin to Sugar
Hollow. The water parting occurs in a swamp, from each end of which a
small brook flows. The height of the pass in this valley--590 feet--
precludes its use as an ancient outlet for Still River. Likewise the
valley east of Town Hill affords no evidence of occupation by a
southward through-flowing stream.
THE ANCIENT STILL RIVER
The conclusion that the Still-Umpog was not reversed by a glacial dam
does not preclude the possibility that this valley has been occupied
by a south-flowing stream. It is probable that in an early stage in
the development of the drainage, the streams of the Danbury region
reached Long Island Sound by way of the Still-Umpog-Saugatuck valley.
Along this route, as described under the heading "The Still-Saugatuck
Divide," is a fairly broad continuous valley at a higher level than
the beds of the present rivers. A south-flowing river, as shown in
fig. 9, brings all the drainage between Danbury and the Housatonic
into normal relations.
This early relationship of the streams was disturbed by the reversal
of the waters of the ancient Still in the natural development of a
subsequent drainage. The Housatonic lowered the northern end of the
limestone belt, in the region between New Milford and Stillriver
village, faster than the smaller south-flowing stream was able to
erode its bed. Eventually a small tributary of the Housatonic captured
the headwaters of the south-flowing river, and by the time the latter
had been reversed as far south as the present divide at Umpog Swamp,
it is probable that the advantage gained by the more rapid erosion of
the Housatonic was offset by the Saugatuck's shorter course to the
sea. As a result the divide between Still and Saugatuck Rivers at
Umpog Swamp had become practically stationary before the advent of the
glacier.
The complex history of Still River is not fully shown in the stream
profile, for the latter is nearly normal, except in the rock basins in
the valley of the Umpog. This is due to the fact that changes in the
course of the Still, caused by the development of a subsequent
drainage through differential erosion, were made so long ago that
evidence of them has been largely destroyed.
The foregoing conclusion practically eliminates hypothesis IV--that
the Still developed from the beginning as a subsequent stream in the
direction in which it now flows. This hypothesis holds good only for
the short portion of the lower course of the present river, that is,
the part representing the short tributary of the Housatonic which
captured and reversed the original Still.
DEPARTURES OF STILL RIVER FROM ITS PREGLACIAL CHANNEL
Between Danbury and Beaver Brook Mountain the Still departs widely
from its former channel, as shown in fig. 6. At the foot of Liberty
Street in Danbury the river makes a sharp turn to the southeast, flows
through a flat plain, and for some distance follows the limestone
valley of the Umpog, meeting the latter stream in a swampy meadow. It
then cuts across the western end of Shelter Rock in a gorge-like
valley not over 200 feet wide. Outcrops of a gneissoid schist on the
valley sides and rapids in the stream bear witness to the youthfulness
of this portion of the river channel.
An open valley which extends from the foot of Liberty Street in a
northeasterly direction (the railroad follows it) marks the former
course of Still River, but after the stream was forced out of this
course and superimposed across the end of Shelter Rock by the
accumulation of drift in the central and northern parts of the valley,
it was unable to regain its old channel until near Beaver Brook
Mountain. The deposits of drift not only have kept the Still confined
to the eastern side of its valley but have forced a tributary from the
west to flow along the edge of the valley for a mile before it joins
its master stream.
About a mile north of Brookfield Junction, Still River valley begins
to narrow, and at Brookfield the river, here crowded to the extreme
eastern side, is cutting a gorge through limestone. The preglacial
course of the Still in the Brookfield region seems to have been near
the center of the valley where it was joined by Long Brook and other
short, direct streams draining the hillsides. The glacier, however,
left a thick blanket of drift in the middle of the valley which turned
the Still to the east over rock and forced Long Brook to flow for more
than a mile along the extreme western side of the valley.
[Illustration: ~Fig. 9.~ Early stage of the Rocky-Still River,
antedating preglacial course shown in figure 4.]
The broad valley through which the Still flows in the lower part of
its course extends northward beyond it for over two miles, bordering
the Housatonic River. At Lanesville near the mouth of the Still, the
river has cut a gorge 30 feet deep and one-quarter mile long in the
limestone. Upstream from this gorge the river meanders widely in a
flat valley, whereas on the downstream side it has cut a deep channel
in the drift in order to reach the level of the Housatonic. There is
room in the drift-covered plain to the west for a buried channel of
Still River which could join the Housatonic at any point between New
Milford and Stillriver station. If the depth of the drift be taken at
25 feet, there would seem to be no objection to the supposition that
the Still initially joined its master stream opposite New Milford, as
shown in fig 6. After the limestone had been worn down to approximate
baselevel, the tendency of the Still would have been to seek an outlet
farther south in order to shorten its course and reach a lower level
on the Housatonic. This stage in the evolution of the river may not
have been reached before the ice age, and it is thus possible that
glacial deposits may have pushed the river to the extreme southern
side of its valley, superimposed it over rock, and forced it to cut
its way down to grade.
SUGGESTED COURSES OF HOUSATONIC RIVER
As possible former outlets for the Housatonic, Hobbs has suggested the
Still-Umpog-Saugatuck valley or the Still-Croton valley (by way of the
East Branch Reservoir)[12], whereas Crosby has suggested the Ten
Mile-Swamp River-Muddy Brook-Croton River valley (by way of Webatuck,
Wing's Station, and Pawling), or the Fall's Village-Limerock-Sharon-
Webatuck Creek-Ten Mile valley.[13] The sketch map, fig. 10, indicates
the courses just outlined and one other by way of the Norwalk. The
latter is the route followed by the Danbury and Norwalk Division of the
Housatonic Railroad. It is natural to assume that the Housatonic might
have occupied anyone of these lines of valleys, particularly where they
are developed on limestone and seem too broad for the streams now
occupying them. Nevertheless, although each of these routes is on soft
rock and some give shorter distances to the sea than the present course,
it is highly improbable that the Housatonic ever occupied any of these
valleys. For had the river once become located in a path of least
resistance, such as is furnished by any of these suggested routes, it
could not have been dislodged and forced to cut its way for 25 miles
through a massive granitic formation, as it does between Still River
and Derby, without great difficulty (Pl. IV, A).
[Illustration: ~Fig. 10.~ Five suggested outlets of Housatonic River.]
An inspection of the larger river systems of Connecticut shows that
the streams composing them exhibit two main trends. Likewise, the
courses, of the larger rivers themselves, whether trunk streams or
tributaries, combine these two trends, one of which is
northwest-southeast and the other nearly north-south.
The north-south drainage lines are the result of geologic structure,
and many broad, flat-floored valleys, often apparently out of
proportion to the streams occupying them, have this direction. On the
other hand, the northwest-southeast drainage lines across the strike
of formations, coincide with the slope toward the sea of the uplifted
peneplain whose dissected surface is represented by the crests of the
uplands. The valleys of streams with this trend are generally narrow,
and some are gorges where resistant rock masses are crossed. The
northwest-southeast trends of master streams thus were determined
initially by the slope of the peneplain, whereas the north-south
trends represent later adjustments to structure.
It is concluded, therefore, that the Housatonic between Bulls' Bridge
and Derby (fig. 10), had its course determined by the slope of the
uplifted peneplain and is antecedent in origin. The old headwaters
extended northwest from the turn in the river near Bull's Bridge,
whereas that part of the river above Bull's Bridge was initially a
minor tributary. This tributary, because of its favorable situation,
in time captured all the drainage of the extensive limestone belt to
the north and then became part of the main stream. The lower
Housatonic, therefore, has always maintained its ancient course
diagonal to the strike of formations, and differential erosion, which
reaches its maximum expression in limestone areas, is responsible for
the impression that the Still River lowland and other valleys west of
the Housatonic may once have been occupied by the latter stream.
[Illustration: ~State Geol. Nat. Hist. Survey Bull. 30. Plate IV.~
A. View down the Housatonic Valley from a point one-half mile
below Still River station. Pumpkin Hill, a ridge of resistant
schist and quartzite, stands on right. A small island lies in
the river.
B. Part of the morainal ridge north of Danbury. Till capped by
stratified drift one mile north of Shelter Rock.]
[Footnote 12: Hobbs, W. H., Still rivers of western Connecticut: Bull.
Geol. Soc. Am., vol. 13, p. 25, 1901.]
[Footnote 13: Crosby, W. O., Notes on the geology of the sites of the
proposed dams in the valleys of the Housatonic and Ten Mile rivers:
Tech. Quart., vol. 13, p. 120, 1900.]
GLACIAL DEPOSITS
BEAVER BROOK SWAMP
A broad belt of limestone extends along the eastern side of the
granite ridge of Shelter Rock and in preglacial time formed a
broad-bottomed valley whose master stream had reached old age. When
the glacier came it hampered the drainage by scooping out the rock
bottom of the valley in places and by dropping deposits at the mouth
of Beaver Brook valley, thus forming Beaver Brook Swamp or "The Flat,"
as it is called (fig. 6).
Among the deposits at the southern end of Beaver Brook Swamp is
considerable stratified drift in the form of smoothly rounded hills or
kames, which are situated both on the border of the valley and in the
swamp. Till containing medium-sized boulders of granodiorite-gneiss
occurs along the road which borders the east side of the densely
wooded swamp.
Along the northeastern border of the swamp is a flat-topped terrace of
till, perhaps a lateral moraine, through which a small stream heading
to the north has cut a V-shaped ravine. A lobe of fine till extends
into the valley from the northeast and narrows the outlet.
Between the railroad and highway, which cross the northern end of the
swamp, is an irregular wooded eminence of rock, partly concealed by a
veneer of drift. Between this knoll and Shelter Rock are heavy
deposits of sand in the form of a short, broad terrace with lobes
which point into the Still River valley. A similar terrace is found to
the northwest on the opposite side of the valley.
At the northern end of Shelter Rock along the blind road leading to
the summit is a peninsula-like body of drift which contains huge
granite boulders mixed here and there with pockets of sand and gravel.
Stratified drift was found at the foot of the hill, and till overlying
it higher up. The more usual arrangement is boulder clay overlain by
modified drift, the first being laid down by the ice itself, the
second being deposited by streams from the melting glacier in its
retreat. Huge boulders, many ten feet or more in diameter, are strewn
over the northern slope of Shelter Rock.
DEPOSITS NORTHEAST OF DANBURY
North of the railroad, opposite Shelter Rock (fig. 6), is a most
interesting flat-topped ridge of drift which topographically is an
extension of the higher rock mass to the northwest. In this drift mass
are to be found in miniature a number of the forms characteristic of
glacial topography. The broad-topped gravel ridge slopes sharply on
the north into a flat-bottomed ravine which is evidently part of the
Still River lowland. This portion of the valley has been shut off by
drift deposits. The drainage has been so obstructed that the stream in
the ravine turns northeast away from its natural outlet. In the valley
of "X" brook (fig. 1) are terraces, esker-like lobes, and detached
mounds of stratified drift resting on a foundation of till.
Along the eastern border of the hill is to be seen the contact between
two forms of glacial deposits (Pl. IV, B). A mass of stratified drift
overlies a hummocky deposit of coarse till, but large boulders
occurring here and there on top of the stratified drift show that the
ice-laid and water-laid materials were not completely sorted. Boulders
seem to have been dropping out of the ice at the same time that gravel
was being deposited. Boulders of granite-gneiss eight feet or more in
diameter, carried by the ice from the hills to the north and
northeast, are strewn at the foot of the hill.
DEPOSITS BETWEEN BEAVER BROOK MOUNTAIN AND MOUTH OF STILL RIVER
About a mile beyond Beaver Brook Mountain, the railroad cuts through
the edge of a hill 80 feet in height exposing a section consisting of
distinctly stratified layers of fine white quartz sand, coarser
yellowish sand, and small round pebbles. The quartz sand was used at
one time in making glass. Farther east where the two tracks of the New
York and New England railroads converge, a cut shows a section of at
least 40 feet of boulder clay. Near the river, limestone boulders are
common, indicating that the valley to the north was degraded to some
extent by the glacier.
[Illustration: ~State Geol. Nat. Hist. Survey Bull. 30. Plate V.~
A. Kames in Still River Valley west of Brookfield Junction.
B. Till ridges on the western border of Still River Valley, south
of Brookfield.]
In the valley at Brookfield Junction and on its western side, are
thick deposits of clean sand. One mile north of Brookfield Junction,
along the western border of the valley, an esker follows an irregular
course for several hundred yards approximately parallel to the river
and terminates at its southern end in a group of kames (Pl. V, A and
B). Opposite the point where these accumulations occur, is a
terrace-like deposit of till. Between the gorge at Brookfield and the
mouth of Still River, swampy areas, flat meadows, and small hills of
drift occur.
In comparison with the Still River lowland, the flat land east of
Green Mountain may be called a plateau. The step between the two is
made by an east-facing rocky slope, the outline of which has been
softened by a lateral moraine separated from the plateau edge by a
small ravine. On the lowland below the moraine is a group of kames.
Near Lanesville (fig. 6), are thick deposits of water-laid material,
including a hill of gravel near the river having a large bowl-shaped
depression on one side formed by the melting of an ice block. Two and
a half miles south of Lanesville on the west side of the lowland, a
wooded esker extends for about one-quarter mile parallel to the valley
axis and then merges into the rocky hillside.
LAKES
The lakes of this region are of two kinds: (1) those due to the
damming of river valleys by glacial deposits and (2) rock basins
gouged out by the ice.
Among the lakes which owe their origin to drift accumulations in the
valleys are Andrew and Haines' ponds at the head of Still River. These
are properly parts of the Croton River system, but Andrew Pond has
been held back by the deep filling of boulder clay in the valley. Lake
Kanosha, in the same valley, is a shallow lake formed in the drift.
The lake south of Spruce Mountain at the head of the Saugatuck seems
to be enclosed by drift alone.
Neversink Pond, Barses Pond, Creek Pond, and Leonard Pond are the
remnants of larger water bodies now converted into swamps. Squantz
Pond and Hatch Pond have dams of drift. Eureka Lake and East Lake
appear to be rock basins whose levels have been raised somewhat by
dams of till. Great Mountain Pond and Green's Pond, between Great
Mountain and Green Mountain, are surrounded by rock and their level
has been raised several feet by artificial dams. Great Mountain Pond
is at least 50 feet above the level of Green Pond and separated from
it by a rock ridge (fig. 2).
HISTORY OF THE GLACIAL DEPOSITS
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
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