From the Coolidge Memorial Bridge the broad lowland seems to reach out
in all directions towards the encircling hills. Far down the river, the
distant bank rises a sheer thirty feet from the water and is high enough
to surmount even the worst of floods. Yet each year this bank recedes as
the unconsolidated sediment at its base is sapped by the stream and is
carried away. Three times the river road has been moved back from the
insatiable Connecticut, and today the main Hockanum highway takes the
long route far from the water's edge.
_The River Works_
Nearer the bridge the land is lower, and it shows the effects of
frequent inundation, but not of scour. A great sand bar lies in the
curve of the stream, and the low parallel ridges suggest that they, too,
were awash in the Connecticut before its eastern bank encroached so far
upon the town of Hadley. The tongue of land which serves as
Northampton's airport is a succession of bars and abandoned channels
which record the migration of the river away from its old bank along
Bridge Street. The Connecticut is robbing Hadley to pay Northampton, but
there was a time when Northampton was pilfered, too.
Swales line the landscape as far as Hadley; and each year, at the time
of high water, they must now be content with the meager overflow, where
once they sped the entire stream upon its southward course. But even
now, in flood, their original function may be restored. For the swale
just west of Hadley was a roaring torrent in 1938, 1936, and 1896.
Indeed, it threatened to appropriate the entire stream, and each of the
great curving hollows that furrow the lowland are scour-channels which
were made at other times.
[Illustration: Fig. 1. _The Connecticut River undercuts the Hadley
bank at Hockanum._]
[Illustration: Fig. 2. _Natural levees border the Connecticut River
south of the Sunderland Bridge._]
The river has moved at will from one side of its alluvial plain to the
other, and its threats to change its course are not to be taken lightly.
Until 1830 it flowed past Northampton, around the great ox-bow to
Easthampton and then back to the watergap between Mount Tom and Mount
Holyoke. It served as the main line of communication to the Atlantic
seaboard and was a much travelled route. In the spring of that year high
water breached the narrow neck of land between the two ends of the
meander loop, and practically overnight the route to New London was
shortened by three miles. Although the event was not a source of
rejoicing to the landowners, Northampton declared a day of thanksgiving
because they were now, thanks be to Providence, three miles nearer the
sea. How often the river has changed its course may never be determined,
but the floodplain is grooved with swampy or silt-filled ox-bow lakes,
not only near Northampton, but all the way from Brattleboro, Vermont, to
Middletown, Connecticut. They tell of older shifts in the course of a
river which still displays its brute power within the limits of its
alluvial plain.
The inundation of 1936 did more than scour the river's floodplain; it
left thick deposits of sand and silt upon many of the fields. Each
preceding flood has done the same sort of thing, dropping coarse sand in
greatest abundance on the banks where the river flowed straightest.
Flood by flood, the deposit has risen higher on these favored sites,
where the swift main current slackens as it spreads over the broad, flat
plain. Today the banks form natural levees sloping away from the river
at many points southward from the Sunderland Bridge.
Just when the river started to shift back and forth across its alluvial
plain is not revealed, but it was long before the white man penetrated
the country. Indian graves and campsites have been laid bare as the high
water of each new flood has removed the silt left during earlier
inundations. The sites rarely yield any implement brought by the
Europeans; they record long years of Indian occupation in the land
called Norwottock, a land in which the red man found a river which
temperamentally shifted its course in response to periodic floods.
The floodplain ends at a rise in the road not far east of Hadley. The
rise is a scalloped embankment, reminiscent of the high bank on the
river bend downstream from Hadley; even the long narrow swamp at the
base looks like a filled ox-bow, and the scallops look like bites which
the hungry river took from its banks. This embankment continues
northward past Mount Warner, following the present channel closely
through North Hadley, and it passes just east of Sunderland village.
Corresponding banks are present on the west side of the stream in South
Deerfield and Hatfield. Within the confines of those terraces the
Connecticut has had free play, but its course has never strayed east or
west of these well defined boundaries.
Wave-like hills of sand cap the embankments in several localities north
of Hatfield and North Hadley. Some, perched on the terrace edge, were
partly cut away when the river was establishing the limits of its
floodplain. Wherever the pine trees are cut down, or the grass plowed
under, the sand within these hills begins to drift. They look and act
like those hills of the desert, the sand dunes, and they record the
drift of wind-whipped sand across a naked land, before the river had
established a floodplain within its present confines.
_The Landscape Changes_
Fine sand, silt, or clay is found beneath the windblown sand wherever
the river banks undercut the dunes. The clays are especially widespread,
for each of the numerous local brickyards has its clay pit, and there
are many more clay banks which have no brickyard. The clays are
rhythmically banded. One band, composed of very fine material which
settles from suspension only after weeks of absolute quiet, retains
moisture tenaciously; adjacent bands dry more rapidly, are somewhat
sandy, and settle from suspension in less than a week. A large body of
quiet water in which so much fine clay could settle must have occupied
the valley before the river was there, and the only type of water body
which could have provided the proper environment is a fresh-water lake,
free from agitation during the long winter months when its surface was
frozen over. These thin clay bands are deposits of a winter season, when
streams are low and their load light. Then, even the finest particles
can settle, during the many weeks of quiet water, as a paper-thin layer
upon the lake bottom. The coarser sandy layer just above the finest clay
records the spring break-up, the melting of the ice, and resuscitated
streams flowing from the hills with a vigor that can be acquired only
when the melt-water from the winter snow combines with the normal
run-off. The sand which these freshets bring to the lake diminishes as
the spring floods subside, and the sediment becomes progressively finer
until next spring comes around.
Pl. 2. _Features of the landscape which originated during
comparatively recent time._
[Illustration: a. _Air view of the ox-bow lake between Northampton
and Mt. Tom._]
[Illustration: b. _Roches moutonnées of the Pelham Hills seen from
Hadley._]
[Illustration: Fig. 3. _Block diagram showing the main features of
central Massachusetts at the present time._]
[Illustration: Fig. 4. _Block diagram showing the main features of
central Massachusetts during the recession of the Ice Sheet._]
Each sandy layer is a spring; each clay band, a winter; and the two
together mark the passage of a year. High spring floods are rarely
local; floods on the Connecticut are usually matched by floods in the
Merrimack watershed to the east and along Housatonic to the west. Floods
of the past were much the same, and many of them can be identified
readily in the banded clays of the Connecticut Valley. Each one can be
traced in contemporaneous deposits which were formed in other parts of
the lowland and in neighboring lake basins.
Some of the winter bands, together with the layers below them, are torn
and folded, and the tops of the folds have been sheared off. Covering
them invariably is the sand layer of the spring break-up. Plain from
these features is a winter episode of freezing to the lake bottom, and
of ice contorting the clays as it expanded and contracted in response to
fluctuations in the surface temperatures. The normal cyclic repetition
of sand and clay was resumed when these particularly hard winters came
to an end.
At South Hadley Falls the lake clays rest upon a gravel bed, and the
bottom layer records the lake's first year of life in that locality. The
overlying bands provide the evidence of a characteristic climatic
sequence which can also be recognized in the clays at Chicopee and at
other points still farther south in the lowland. But at Chicopee there
are many layers which are older than the bottom layer at South Hadley
Falls; and at Springfield many layers appear that are older than the
basal band at Chicopee. From the sediment deposited in its waters, the
story of the lake is not difficult to decipher. It existed at
Springfield years before it appeared at South Hadley Falls; in fact, it
flooded the meadows near Middletown, Connecticut, for nearly 6,000 years
before its waters existed near Northampton.
These beds of clay hold the moisture close to the surface throughout the
lowland, making it available to the fields of vegetables and tobacco.
Towards the valley margins these crops disappear because the fine
sediments end against the rocky shores of the adjacent hills which pass
into and beneath sloping terraces of sand and gravel. In the numerous
terraces which fringe the hills, the horizontal beds of gravel lie above
lakeward-dipping beds of coarse sand; they underlie broad flats furrowed
by channel-like depressions which radiate from the valleys at the apex
of each flat. On these terraces one can easily picture sand-laden waters
coursing through the channels and building deltas outward into the lake.
Deltas were built wherever streams from the highlands entered the
valley, and they mark the ancient level of the lake. Strangely, their
elevation drops from 315 feet at Montague to 300 feet at Amherst, and is
only 268 feet at South Hadley. The changing elevation shows either that
the lake surface sloped southward--and indeed this would be unique--or
that the shoreline was raised in the north and that the lake drained
southward. The latter surmise is plainly the more plausible.
Most deltas on the east side of the valley are pitted by numerous
conical depressions. In a depression on a delta plain near Montague, an
excavation, made to obtain road fill, disclosed a mass of disordered
gravel which must originally have been deposited in the horizontal
top-set beds of the delta, but which now lies in the bottom of a
depression mingled with the fine sand of the underlying fore-set beds.
The top-set beds seem to have been supported for some time and then
collapsed as if the underpinnings were removed. The crudely circular or
elliptical outlines of the depressions suggest that stray icebergs
drifted upon the delta slopes, where they were anchored or buried by the
sandy outwash. The buried ice-cakes survived until the lake was drained,
and the baselevel of the streams was lowered, for the depressions have
no outwash within them. They collapsed soon after the lake vanished,
because water soaking through the delta sands melted the ice, much as it
thaws the ground for dredging in the Yukon. Even today this gravelly
ground, particularly the beach of the ancient lake, is well drained, and
it forms the best land for the apple orchards of the valley.
_Glaciers Came_
The delta deposits and the clays form a thin veneer over a bouldery soil
that comes to light along the delta-top margins and in gulches cut down
through the gravel and sand. Some of the boulders are huge, attaining
diameters of twenty feet; and all are strangers to their present resting
places. Some are set upon a bare rock floor, scratched as though by
sandpaper, and they teeter to the weight of a child; most are embedded
in soil. These "erratics" seem to have been left like unwanted objects,
picked up and carried for a time, and then dropped when the bearer
wearied of their weight. The scratches on the rock floor are parallel
grooves, all of which trend southward. They are unmistakable tracks left
by glaciers, and the boulders are like the stones perched on glacial ice
for a ride to the terminal moraine.
The land above the old lake shore is bare scratched rock or rocky soil
called boulder till. Every hill farm has been cleared of more stones
than trees, and it is only with the vogue of the rock garden that these
erratics have found any merit in man's estimation. It has been said with
a considerable element of truth that the lake margin can be identified
by the stone fences heaped up by exasperated farmers at the line where
the water once lapped the slopes of the glaciated hills. Striations and
erratics decorate the tops of Mount Tom and Mount Holyoke, and those who
visit Mount Monadnock or Mount Washington will find they must inscribe
their initials over the signature of the great ice sheet.
The stranger rocks or erratics, stranded promiscuously over the
countryside, can be traced to hills farther north. Clearly the ice sheet
was moving southward, picking up debris and abrading the countryside
like a great sanding machine. Northern slopes were worn to long gentle
inclines and the southern slopes kept their original forms or were
steepened as the ice plucked fractured blocks from their moorings. One
imaginative writer likened the glaciated rock hills to the wigs of
sheep's wool worn by the jurists of his day; the name stuck, and they
are still known as _roches moutonnées_. Look at the Pelham Hills from
the Coolidge Memorial Bridge and you will see the top of Jeffrey Lord
Amherst's wig facing towards Canada.
Within the Connecticut Lowland the moving ice often picked up a load of
debris more cumbersome than it could drag along. It handled the
situation most satisfactorily by dropping the load and streamlining it,
and these piles of glacial debris with blunt north slopes and gentle
southerly sides are drumlins. When next you pass the apple orchards of
South Amherst, recall that the smooth elliptical hill east of the road
to South Hadley is a drumlin, a relic of an overloaded glacier.
_Just Before the Ice Age_
The glacier advanced as far as Long Island and Martha's Vineyard, and
the lakes of the Connecticut Valley formed along the ice margin and
spread northward as the ice front receded. The distinct layers, or
varves, of clay mark off 25,000 years since the recession began, but for
a million years before its final retreat, the ice covered all New
England intermittently. This length of time transcends human
comprehension unless one considers years in terms of what has been done.
A million years is not too long for a sand-laden ice sheet, moving only
a few feet each year, to grind tens of feet of solid rock off the north
sides of the "everlasting" hills. To those who study the earth, "Before
the Ice Age" has about the same significance as "Before the Hurricane"
has to the average citizen of New England. It is in such terms that
geologic time must be considered.
The ice sheet simply modified the pre-glacial topography; it changed
symmetrical hills to asymmetric _roches moutonnées_ and left boulder
till spread over much of the bedrock floor. The greatest changes were
effected in the White Mountains, where the steep-walled river valleys
were changed to troughs with a U cross-section, as in the scenic
notches; or with steep headwalls like that in Tuckerman Ravine, a
typical alpine cirque. Within the lowlands boulder till was left as a
blanket, concealing the irregularities which were made in the rock floor
at an earlier geologic date. These irregularities may pass unnoticed
unless some construction project happens to reveal them. Bedrock is
rarely over seventy feet down at any point in the lowland, but work at
the Sunderland Bridge and the Coolidge Memorial Bridge encountered
masses of glacial debris in a deep fluvial channel more than three
hundred feet below the river surface and at least two hundred feet below
the present level of the sea. This deep trough is not over one hundred
yards wide, and if it were fully exposed to view, it would look like a
miniature Saguenay gorge. Similar trenches in every part of eastern
North America, from Hudson Bay to Cape Hatteras, show that the land once
stood higher than it does now, and that the main rivers flowed in deep,
narrow canyons, although the upland surface between the rivers had its
present characteristics. Thus, in Pliocene time, while primitive members
of the human race were entering old England, New England rose high above
sea level, and its lowlands were trenched by quickened streams.
The narrow gorges are an eloquent, if mute, record of rivers suddenly
rejuvenated, their current accelerated and the exuberant waters cutting
into freshly elevated rock. Massachusetts and the neighboring states
along the Atlantic seaboard formed a plateau-like upland, perhaps one
thousand feet higher than today, and the coastline lay fifty to one
hundred miles out under the present waters of the Atlantic.
The Pliocene episode of stream incision was of short duration. The
gorges are not wide, and only near the sea do they cut deep into the
coherent crystalline rock which gives New England its solid foundation.
Nowhere did the land remain elevated long enough to permit the rivers to
widen their canyons through the plateau-like country and to modify the
essential features of the landscape. The latter were acquired in an
earlier geologic epoch called the Miocene, and the scenic pattern carved
by running water in that relatively remote division of time still
dominates the region's topographic form.
_Rivers Carried Off the Everlasting Hills_
Every stream has its load of sediment, as the silt- and sand-filled
reservoirs along the edges of the valley so effectively testify. Each
sandy river bed is an aggregate of rolling grains, moving with the
current, slow where it is slow and faster where the current is
accelerated, but travelling always towards the sea. Every grain is a
piece of the countryside lost to the land and soon to become a part of
the ocean floor. Very little of this sand comes from the lowland itself,
for the Connecticut may cut the bank below Hadley, but it leaves almost
as much sand as it acquires on the opposite shore. The river's burden is
brought to it by swift tributaries--the brook at West Pelham and
hundreds more like it. Their sides are cut-banks, but no extensive sand
bars are built to balance their erosive work; what they pick up they
carry to the lowland, and what they bring to the lowland is soon
transported to the sea.
The contribution which the tributaries make to the lowland rivers was
demonstrated only too conspicuously by the great fans of coarse debris
spread across the valley of the Deerfield River and the West River
during the floods that accompanied the torrential rains of the
hurricane. Parts of the village of Townshend, Vermont, nestling in the
flat floor of the West River valley, were buried in gravel wash, and the
hillside roads above were gullied ten feet deep. One harassed traveler
aptly remarked that the original road level could be recognized from the
few concordant remnants of pavement beside the trout brook.
The hill slopes at Townshend rise and end near Jamaica, about one
thousand feet higher in elevation. Here the roads are in good condition.
There are no signs of erosion, and the rolling uplands extend for miles
with no signs of gullying or wash by the heavy rains.
The debris handled by the West River now and for ages past has come from
the steep hill slopes along the main valley. Each load of sand has cut
these slopes back from the main stream and has widened the lowland
floor. So, for millions of years, the tributaries of the Connecticut
have pushed the valley walls farther from the main river, and their
tributaries in turn have pushed their hill slopes back, while the valley
floors have steadily widened. The Connecticut Lowland was broadened in
this way, and the tributary Deerfield has developed its valley in
similar fashion but to a lesser degree. Today streams near the
headwaters acquire sediment, not from the upland across which they flow
to reach the deeply entrenched valleys, but from the steep slopes in the
most remote recesses of the upland on which they rise.
Flat valley floors are broadened in coherent rocks as well as in
unconsolidated sand--less rapidly, indeed, but just as surely; and every
region is worn down to the grade of the streams which drain it, except
for those rare masses of resistant rock which defy decay and yield
reluctantly to their inevitable fate. The rocks of the Mount Holyoke and
Mount Tom ranges, Mount Warner, the Pocumtuck Hills and the highlands on
both sides of the Connecticut Valley are made of tougher ingredients
than the lowland, and even millions of years of incessant onslaught by
running water did not suffice to level them by Miocene time, when the
lowland was excavated.
Pl. 3. _Erosion remnants or monadnocks surmounting base levelled
surfaces._
[Illustration: a. _Mt. Sugarloaf, a remnant of Triassic rocks
disappearing grain by grain down the Connecticut River._]
[Illustration: b. _Mt. Monadnock, a hill surmounting the New England
peneplain, seen from Mt. Lincoln._]
[Illustration: Fig. 5. _Block diagram showing the main features of
central Massachusetts during the excavation of the lowland._]
[Illustration: Fig. 6. _Block diagram showing main features of
central Massachusetts after the Triassic basins were filled._]
The lowland extends beyond our immediate region. It continues southward
with diminishing elevation to New Haven, where it joins another broad
depression, now flooded by the waters of Long Island Sound.
_Before the Rivers Cut the Valleys_
Those who would see the land as it was before the rivers carved the
lowlands must put back every grain of sand the waters carried away; they
must fill in these valleys to the level of the Jamaica upland. Then only
will the country be as it was before the streams were rejuvenated and
started to cut deep trenches and to widen them as the Deerfield has done
at Charlemont.
Broad, open valley flats or straths surmount the steep V-shaped notches
of both the Deerfield and Westfield Rivers. Surely, everyone who has
paused at the lookout on the east summit of the Mohawk Trail has seen
the upland sloping gently towards the Deerfield and then breaking
sharply at the top of the present canyon. The same view confronts the
motorist who drives from Adams to Cummington, just after he leaves the
village of Plainfield. Here the shallow bowl in front of him holds no
hint of the deep notch in which the Westfield flows. The gentle contour
of the land suggests only the slow but methodical sort of change which
comes with maturity. Those who favor air travel will see, as they fly
over Mount Tom, a similar but more dissected strath reaching into the
hills northwestward from Northampton. Aeroplanes flying the Boston-New
York route pass over straths which have been trenched by the Connecticut
along its course from Middletown to New London.
The straths are part of a mature, but ancient drainage system, which was
graded a thousand feet above the level of the present streams and only a
few hundred feet below the main upland. Certain broad depressions
through the highlands east of the Connecticut Lowland suggest that this
drainage pursued a southeastward course to the Atlantic, and that the
river did not establish its modern course until the straths were
elevated and notched.
The land level above the strath-margins is a still older surface from
which the rock-benches were cut. The higher surface stretches to the
horizon at Pelham, but Mount Monadnock and Wachusett stand conspicuously
above it. And on the Mohawk Trail one must ascend the tower at the
eastern summit before any higher land comes into view. Greylock's summit
and the long chain of the Green Mountains attain greater elevations. The
West River and Deerfield basins are graded to the level of this higher
and older erosion surface, but farther north a chain of peaks including
Stratton and Okemo swing eastward towards Ascutney. They appear to have
formed a divide on this ancient land, as they do today; and beyond their
crests rivers have run to the Saint Lawrence and Hudson basins from a
time which antedated any of the familiar features of the New England
landscape.
Although this flat upland surface is more complex than it appears to the
eye, it dominates all of southern New England, and ramifying arms of it
penetrate northward into the White Mountains of New Hampshire and Maine.
Another great arm passes west of Mount Greylock and spreads out between
the Catskill Mountains and the Adirondacks. During the long period of
erosion when it was formed, New England was reduced nearer to the grade
of the main rivers than at any other time either before or since, and
only rocks which have effectively resisted all later assaults by the
geologic processes of destruction surmount the surface. To the eye, the
region appears so nearly planed that it has been called the New England
peneplane.
The upland continues southward through the Berkshire and Litchfield
Hills, descending in a series of almost imperceptible steps towards Long
Island Sound and the Atlantic. A few miles south of Litchfield,
Connecticut, its low angle of declivity increases abruptly, and the more
steeply inclined surface passes beneath the waters of Long Island Sound.
The sudden change in dip suggests that two erosional planes are present
and that each was formed under somewhat different circumstances and in
different periods of geologic time. The soundness of this surmise can be
demonstrated in Long Island where sediments laid in a Cretaceous sea
rest upon the older and more sharply inclined erosional plane and rise
approximately to the level of the New England upland. The deposits form
a wedge between the two planes, and their Cretaceous age supplies a
series of dates that would otherwise be difficult to establish in New
England's geological history. Erosion fashioned the New England upland
in the early and middle epochs of the Tertiary period, immediately
following the deposition of sediments in the Cretaceous sea. And the
southward sloping plane upon which those sediments rest records an even
earlier episode of denudation--an episode lost in the shuffle of later
events in Massachusetts but preserved in fragmentary form in
Connecticut, thanks to the protection afforded by the sedimentary cover.
Had we lived in central New England when erosion of the upland and of
the younger straths was in progress, we would have noted that the valley
forms were well defined in the headwaters and lower reaches of the
streams, which made their way through a country of light-colored or gray
clayey soil. In the middle reaches the valley boundaries were blurred
and indistinct, and the country through which they flowed was surfaced
by red and sandy soil. The middle region is now the lowland, but even
then it formed a depression athwart the topographic and hydrographic
features of the country; and its distinctive red soil resembled alluvial
wash or fill in a long basin. Its low relief would have been as
impressive in early Tertiary time as its higher relief is today, for
then it had little topographic competition anywhere between the present
sites of New Haven, Connecticut, and Northfield, Massachusetts.
The land had one dominant characteristic--a relatively flat or faintly
terraced surface. But this surface concealed a mosaic made of an
infinite variety of rocks, each responding to the attack of weather in
its own particular way. Erosion has brought out the pattern of the
mosaic, and we have retraced the steps in its development. Viewing the
evolution of the countryside in retrospect, we see its features take
form much as a worker on an inlaid bronze might watch the design come
out when it is etched. The creation of the mosaic or inlay is another
part of the history, and the relief of the land now permits closer
scrutiny of the pattern than would have been possible in Cretaceous
time.