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Geological History of
the Connecticut River Valley
By Prof. Richard D. Little


Introduction

For 410 miles from near the Canadian border to Long Island Sound, the Connecticut River, New England's longest and widest river, runs to the sea. Along the way it marks the boundary between New Hampshire and Vermont and slices prominently across Massachusetts and its namesake, Connecticut. It is truly a river that "connects". It is a very diverse river that sometimes flows quietly, meandering over a broad, fertile floodplain, and at others rushes over prominent waterfalls and rapids (important waterpower locales) or through narrow gorges.

The beauty of this river has long been noted. Former Yale President Timothy Dwight wrote the following in the early 19th century: "This stream may, with more propriety than any other in the world, be named THE BEAUTIFUL RIVER. ...The purity, salubrity and sweetness of its waters; the frequency and elegance of its meanders; its absolute freedom from aquatic vegetables; the uncommon and universal beauty of its banks, here a smooth and winding beach, there covered with rich verdure, now fringed with bushes, now covered with lofty trees, and now formed the intruding hill, the rude bluff and the shaggy mountain, are objects which no traveler can thoroughly describe and no reader can adequately imagine." (Quoted in Delaney, p. 9)

GEOLOGIC HISTORY

The rocks and landscape of the Connecticut Valley region record events of ancient times from colliding and splitting continents (Paleozoic and Mesozoic Eras, respectively) to glacial processes (which ended about 10,000 years ago) in a particularly clear and dramatic fashion. (Bain & Meyerhoff, 1976; Bell, 1985; Little, 1986, 1994; Raymo & Raymo, 1989)

Paleozoic Era

(570 - 225 million years ago)

Although some rocks in the Connecticut Valley drainage are older, dating back over 1 billion years (Precambrian Era), most of the early geologic history is involved with the creation of the supercontinent of Pangea during the Paleozoic. Tectonic plates of the Earth's crust drift together during the Paleozoic eventually leading to the merging of North America with Africa and Europe. The collision of these plates not only closed an early version of the Atlantic Ocean, known as Iapetus (the father of Atlas in Greek mythology) or the Proto-atlantic, but also created one of the greatest mountain chains in the world, the Appalachians.

The Paleozoic rocks of New England record their origins as deposits in the Iapetus Ocean, either as sedimentary rocks perhaps washed in by rivers or formed from shells or reefs (we were south of the equator during much of the Paleozoic), or igneous types from volcanic eruptions or deep magma chambers where slow cooling produced the easily seen minerals of granite rock. The heat and pressure of the collision process transformed these rocks into metamorphic types.

Mesozoic Era

(225 - 65 million years ago)

The Connecticut Valley originated in the Mesozoic. Pangea began to split, forming the present Atlantic Ocean. Besides the big split of the Atlantic, many smaller faults cracked the land due to the stretching stresses. These "rift valleys," similar to today's Death Valley and others of the Basin and Range, formed the initial drainage of the ancestral Connecticut Valley.

The fault that dominated the Mesozoic rift was located on the eastern side of the valley, and is known as the Eastern Border Fault that can be traced from New Haven, CT. to Keene, NH. Rivers rushed into the rift valley and deposited sedimentary materials, gravel, sand, and mud. Gravely alluvial fans were major deposits along the mountainous eastern margin of the old valley, while sandy-muddy floodplain, shoreline and lake deposits dominated the lower valley elevations.

One of the unique aspects of the Connecticut Valley of today is that sedimentary rock from the processes just described, is easily seen along the rocky river bends and roadsides in the MA and CT portions of the valley. Since almost all of New England is composed of metamorphic rock (due to the Paleozoic collision), these rusty sedimentary layers from alluvial fans and lake beds provide important geological examples and evidence of our Mesozoic history, including some world-class fossils.

Fossils, evidence of or remains of ancient life, are abundant in the shales and sandstones representing deposits in old shoreline and lakebed environments. Most common are fossils that represent the tracks, trails, and burrows of insects or other invertebrates. Rarer and more important are fossils of dinosaurs and fish. "By the middle of the nineteenth century, the Connecticut Valley had achieved worldwide acclaim for its paleontology, particularly its reptile footprints and fishes." (McDonald, 1991, p.91)

Dinosaurs are mainly preserved as footprints preserved in the Mesozoic sedimentary rocks of the Connecticut Valley in MA and CT. Very few bones have been discovered since bones decay, while each animal can leave countless footprints along the muddy shores of rivers and lakes. The first scientific study of dinosaur footprints in the world began in 1835 as paving stones, quarried from along the river in the Turners Falls, MA area, were being laid in Greenfield, MA. Professor Edward Hitchcock, geologist, theologian, and president of Amherst College, became world renown for his three-decade detailed study of the region's prints (Hitchcock, 1858, 1865). Hitchcock's famous and important collection of dinosaur prints is now preserved at the Pratt Museum of Amherst College.

A more recent footprint discovery of world importance occurred in 1966 at a construction site about a mile from the river in Rocky Hill, CT. Dinosaur State Park is now located at this site and under its broad domed building can be seen an exposed shale bedding plane with about 500 large (12" - 18") prints. Over 1500 other prints have also been studied, but are now reburied for preservation. Dinosaur expert Dr. John Ostrom of Yale states that "The Rocky Hill site is remarkable in that it is perhaps the largest (more than 35,000 square feet) known exposure with abundant fossil footprints preserved on a single bedding plane." "Aside from the impressive spectacle of so many footprints and such a large expanse, this site contains an unusual record of a 'single moment' in .. time." "Rocky Hill can provide us with new information on animal associations, habits, and movement that cannot be obtained from other ... sites." (Ostrom, 1968) In fact, Dr. Walter Coombs determined that some of these carnivorous trackmakers were able to swim, based on foot and claw impressions in the old lake bottom shale. (Coombs,1980)

At another site bordering the river in Holyoke, MA, Ostrom has described 19 trackways that indicate, because of their parallel orientation, herding behavior. (Ostrom, 1972)

The Connecticut River Valley is also the site of a few excellent fossil fish localities. About 20 productive sites are presently known, preserved in black shales of old lake beds, and commonly yield whole specimens (McDonald, 1975), undisturbed by scavengers or wave action in Mesozoic lakes.

A sedimentary feature that is unique to the Connecticut Valley is the armored mud balls found in Turners Falls, MA and vicinity. Armored mud balls formed in the Mesozoic sedimentary layers as streams rolled balls of hard mud downstream. The mud became round as well as soft and sticky on the outer margin, allowing sand and pebbles to become attached (the armor). The balls were quickly buried by other stream deposits and eventually lithified. Lithified armored mud balls have only been found in about 10 other localities in the world, in old beach deposits. The Turners Falls area armored mud balls are the only stream-formed armored mud balls in the world. (Little, 1982) Excellent examples of these forms are preserved in boulders placed along the river at Unity Park, Turners Falls, and in the Greenfield Community College "Rock Park".

Lava flows are dramatic and important Mesozoic events in the Connecticut Valley and profoundly influence the landscape today. The dark basalt lavas, called "traprock", flowed out over the Mesozoic lowlands, commonly reaching over 100 feet in thickness. Today these flows, tilted by movements along the ancient Eastern Border Fault and then exposed by erosion, form spectacular ridges that stretch tens of miles, creating interesting, dramatic vista points and important upland ecosystems in the middle of the wide valley (Fig. 5). Examples include the Pocumtuck Range (Greenfield - Deerfield, MA) and the Holyoke Range that trends east-west about 10 miles from Amherst to Easthampton, and then southerly for about 60 miles (known as the Metacomet Ridge) to the outskirts of New Haven.

The basalt flows exhibit interesting geologic features such as pillows, formed by flow underwater, and columns, created by contraction cracks during cooling. The basalt is an important geologic resource, quarried for crushed stone and rip-rap.

By the end of the Mesozoic Era, 65 million years ago, the Eastern Border Fault had been inactive for about 70 million years allowing the valley to become completely filled with sedimentary deposits. Surrounding areas were smoothed by erosion and all became part of a peneplain, an erosional plain of regional extent. Several high places resisted the forces of erosion, and are known as monadnocks, named for a prominent example of this feature, Mt. Monadnock of southwestern NH.

Cenozoic Era

(65 million years ago - present day)

During the Cenozoic uplift raised the peneplain hundreds of feet, resulting in prominent down cutting by streams to create the basic valley forms of seen today. Erosion proceeded faster in the weak sedimentary rock areas leaving the more resistant rocks higher on the landscape, thus creating the prominent ridges of basalt lava mentioned above as well as the highlands (metamorphic rock) on either side of the Connecticut Valley.

With the uplift of the peneplain the Connecticut River's course gradually developed in a north-south direction, following geologic trends. However, a prominent divergence occurs at Portland, CT. The river flows southeast, leaving wide lowlands developed in soft rock of the Mesozoic rift valley to erode a narrow valley across 30 miles of hard metamorphic rocks of the eastern highlands to finally end at Long Island Sound. Since this exit to the sea corresponds with the trend of the Farmington River, it seems that the Connecticut appropriated this pathway.

The remainder of the Mesozoic rift valley with sedimentary rocks and lavas continues southerly to New Haven with no river of any consequence.

Glaciation profoundly affected the region as continental glaciers moved southward from Canadian source areas. While the Earth has been in the grip of the Ice Age for about 2 million years, it is the last ice advance, known as Wisconsinan, that is most important. The Wisconsinan ice was at its maximum only 20,000 years ago, only "yesterday" in geologic time. The ice sheet completely covered the Connecticut River drainage and surrounding areas, ending at the terminal moraine deposits of Long Island, NY, Marthas Vineyard, and Nantucket, MA.

During ice retreat, glacial meltwater deposits filled the Connecticut Valley in the New Britain - Rocky Hill area to create a dam. As the ice continued to melt back to the north, water backed up behind this dam, forming Lake Hitchcock, which, over the course of about 4,000 years, gradually extended up the Connecticut River drainage as far north as West Burke, VT, a distance of about 250 miles. Approximately 12 or 14,000 years ago Lake Hitchcock drained, allowing the Connecticut River to once again flow across its valley.

Many deposits filled Lake Hitchcock. Deltas were built into the lake by both tributary streams glacial meltwater. (Meltwater deltas are known as kame deltas.) These deposits are important sand and gravel deposits as well as aquifer zones. Lake bottom areas accumulated mud in annual layers called "varves". The varves can be counted and correlated like tree rings and help to trace the timing and events that shaped the lake. They also were the source of the valley's former brick industry, and are mined today for landfill lining and capping.

The climate remained cold enough to create permafrost in the soil after Lake Hitchcock drained. One of the permafrost features of significance is the pingo. Pingos are volcano-like ice blisters, perhaps 50 feet high. When the ice melted, shallow lakes remained on the landscape and some are even seen today, over 12,000 years later.

After draining, the Connecticut River and tributaries cut through the Hitchcock deposits, creating terraces and floodplains that are prominent features of today's landscape. Remnants of Lake Hitchcock's shoreline and lake bottom are also preserved as terrace levels high above the river. The stone-free, productive bottomlands that makes the Connecticut River Valley an agricultural paradise is due to this combination of old lake bottom clay capped by fluvial flood deposits, supplemented by the groundwater resources of nearby aquifers.

In places the Connecticut River was not able to find its preglacial course after Hitchcock's drainage, and instead of a wide, floodplained valley, the river found itself flowing over bedrock creating waterfalls and rapids, or coursing through a narrow valley. At its mouth, the river has been flooded by the sea, a consequence of glacial melting and worldwide sea level rise. In fact the lower river is an estuary, with tidal effects as far as Hartford. Extensive marshland dominates the river's end -- the only major American river not having a city at its mouth (Stekl & Hill, 1972), and beaches built at least in part from the river's flow, form final deposits as land and sea connect (Patton & Kent, 1991).

The unique combination of geology and landforms gives the Connecticut River Valley an outstanding landscape diversity. Its an excellent natural laboratory for exploration and recreation.

References Cited

Bain, G. and Meyerhoff, H., 1976, The Flow of Time in the Connecticut Valley: Geologic Imprints, CT Valley Historical Museum, Springfield, MA, 168 p.

Bell, Michael, 1985, The Face of Connecticut, Bull. 110, State Geol. and Nat. Hist. Surv., Hartford, 196 p.

Coombs, Walter P., 1980, Swimming ability of carnivorous dinosaurs, Science, v. 207, p. 1198-1200.

Delaney, Edmund, 1983, The Connecticut River, New England's Historic Waterway, Globe-Pequot, 182 p.

Hartshorn, J. and Colton, R., 1967, Geology of the southern part of glacial Lake Hitchcock and associated deposits, in Robinson, P., ed, Guidebook to field trips, New England Intercollegiate Geological Conf., Amherst, MA, p. 73-88.

Hitchcock, E., 1858, Ichnology of Massachusetts, W. White State Printer, Boston, 205 p.

---------, 1865, Supplement to the Ichnology of New England, Wright and Potter, State Printers, 96 p.

Hubert, J., 1978, Paleosol caliche in the New Haven Arkose, Newark Group, CT, Palaeogeog. Palaeoclim. Palaeoecol., v. 24, p. 151-168.

Lee, C., 1985, West Rock to the Barndoor Hills: The Traprock Ridges of CT, State Geol. and Nat. Hist. Surv., Vegetation of CT Natural Areas no. 4, Hartford, CT., 60 p.

Little, Richard D., 1982, Lithified armored mud balls of the lower Jurassic Turners Falls Sandstone, north-central MA, Jour.Geology, v. 90, p. 203-207.

----------, 1986, Dinosaurs, Dunes, and Drifting Continents: The Geohistory of the Connecticut Valley, Valley Geology Publications, 107 p.***(This book is being significantly revised and will be available (tentatively) Fall, 2000)

----------, 1994, The Flow of Time: 500 million years of Geohistory in the Connecticut River Valley, 35 min. videorecording, Pioneer Valley Institute, Greenfield Community College, Greenfield, MA

McDonald, Nicholas, 1975, Fossil fishes from the Neward Group of the Connecticut Valley, MA Thesis, Wesleyan Univ., Middletown, CT, 230 p.

----------, 1991, Paleontology of the Early Mesozoic (Newark Supergroup) Rocks of the Connecticut Valley, in Mattson, L., ed., Geology of Western New England -- Field Trip Guidebook and Proceedings, Nat. Assoc. Geol. Teachers, Eastern & New England Section Ann. Mtg., Greenfield Comm. Coll., Greenfield, MA, 131 p.

Olsen, P., 1986, A 40-million-year lake record of early Mesozoic orbital forcing, Science, v. 234, p. 842 - 848.

Olsen, P., McCune, A, Thomson, K., 1982, Correlation of the early Mesozoic Newark Supergroup by vertebrates, principally fishes, Am. Jour. Sci, v. 282, p. 1-44.

Ostrom, J, 1968, Geology of Dinosaur Park, Rocky Hill, CT, in Orville, P., ed., New England Intercollegiate Geological Conference Guidebook, Guidebook No. 2, CT Geol. and Nat. Hist. Surv., Hartford, CT, p. 1-12 (c-3).

__________, 1972, Were some dinosaurs gregarious?, Palaeogeog. Palaeoclim. Palaeoecol., v. 11, p. 287-301.

Patton, P. and Kent, J., 1991, A Moveable Shore: the face of the CT coast, Duke Univ. Press, 159 p.

Raymo, C. and Raymo, M., 1989, Written in Stone: A Geological History of the Northeastern United States, Globe-Pequot, 163 p.

Stekl, W. F., & Hill, E., 1972, The Connecticut River, Wesleyan Univ. Press, 143 p.

Stone, J. and Ashley, G., Ice-wedge casts, pingo scars, and the drainage of Lake Hitchcock, p. 305-331, in Robinson, P. and Brady, J., eds, Guidebook for field trips in the Connecticut Valley Region of MA and adjacent states, 84th Annual Meeting, New England Intercollegiate Geological Conf., 1992, Contrib. 66, Univ. of MA Dept. of Geol. and Geog., Amherst, MA, 535 p.

Contact Information

Earth View LLC
Geology Education Products and Services
C/O Prof. Richard D. Little
6 Grand View Lane
Easthampton, MA 01027-1075

Phone / Fax (413) 527-8536
rdlittle2000@aol.com