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When LI Sound Was A Lake

June 30, 2020

Sometime around 19,000 years ago, Long Island Sound was a freshwater lake! Had you, at the time, been able to walk its beaches, you might have seen icebergs floating on its surface and its waters clouded by fine glacial sediments. As the lake grew, it evolved into what would become an important waterway and a rich estuarine (mix of fresh and salt water) habitat for marine life.
Canadian glaciers covered parts of North America at least 16 times over the earth’s early history. Some 85,000 or more years ago, the last glacier, the Laurentide Ice Sheet, had spread across most
of Canada. Reaching Wisconsin some 31,500 years ago, it became known as the Wisconsinan Glacier. From there, its ice advanced southward eventually reaching the Missouri and Ohio Rivers. At some northerly locations, its thickness is believed to have attained a height of about 6,000-7,000 feet (1.3 miles)! The glacier covered most of northern New England including Connecticut, Rhode Island and Massachusetts. Ice over Hartford was estimated to have been about 2,500 feet thick; New Haven’s was about 1,800 feet thick. Sheet ice is also said to have managed to cover New Hampshire’s Mt Washington, standing at 6,288 feet above sea level! In the meantime, the glacier spread across parts of Long Island where its remnants, called terminal moraine, marked the extent of glacial ice. One possible relic of the glacier, a nearly one and half+-story tall boulder, stands at the north-west corner of Smithtown Bay, New York. Other massive boulders lie submerged in Long Island Sound, with some located just offshore of Long Island. In Block Island Sound, a 16 to 20+ feet tall boulder is frequently explored by scuba divers. The rocks serve as habitat for some of the area’s fascinating marine creatures.
As they advanced across North America, the glaciers bulldozed larg

e amounts of rock and debris, sometimes digging as far as down as 65 feet below the surface. The glacier’s weight also compressed the land. However, it later rebounded as the ice melted and retreated. With so much of the ocean’s waters incorporated into glacial ice, global sea levels eventually dropped by some 300 feet! By that time, the shoreline south of Long Island, is said to have extended out 50 to 70 or more miles.
By approximately 26,000 years ago, the Wisconsinan glacier had reached its maximum expansion. The glacial materials that were deposited at the edge of its spread, added to Long Island’s landscape. Then, around 20,000 years ago, the glacier began to melt. As it retreated from areas that it had covered, it did so in spurts, leaving behind its calling card, recessional moraines. Glacial spoils added to the surface of Connecticut’s Great Captain’s Island, the Norwalk Islands and Falkner Island off Guilford. Farther north, the ice sheet remains contributed to the above-water portions of Fishers and Plum Islands. In the vicinity of the present-day Race, just off the south end Fishers Island, piled-up glacial debris produced a moraine dam. It served to withhold melting ice water, allowing its retention in the basin partially developed by the glacier. The meltwater-fed Connecticut Glacial Lake eventually grew to the approximate size of today’s Long Island Sound. Though the open Sound’s depth varies from 65 to 230 feet, clay sediments, deposited by the glacier, contributed to its average depth of about 64 feet.
Long Island Sound’s freshwater lake, which may have lasted about 3,000 years, was according to Connecticut’s geologist Ralph Lewis, considerably deeper and obviously much colder than today’s Sound. It was further believed that it may have been devoid of any species of fish. But by around 15,000 years ago, melting glaciers allowed the seas to rise sufficiently to breach the moraine dam. The future Long Island Sound was then gradually invaded by ocean salt water with its accompanying tides and currents.
    As the glaciers had retreated northward and out of Connecticut, they left behind a vast treeless tundra with little plant life. In time, reforestation began, accompanied with sufficient plant life to allow return of mastodons. They would roam Connecticut, New York and many other sites. Distant relatives of elephants, these ancient mammals were 8 to 10 feet tall. The males were equipped with tusks that could reach 8 feet in length.
Herds of the ancient mammals occupied parts of North America between 125,000 to approximately10,000 years ago, when they became extinct. Just what caused their extinction is unsure. Was it disease, overexploitation by early hunters, global temperature change following the ice age or a combination of these factors?
In 1845, a mastodon skeleton was unearthed in a Newburg, New York bog. As described by investigators, the 11,000 years old remains were “one of the most complete mastodon skeleton ever found.” When unearthed, it was found standing upright with its legs stretched forward, as if trying to free itself from the soggy bog. This same awe-inspiring, prehistoric mammal’s skeleton, now stands tall on display at New York’s American Museum of Natural History. It is said that Founding Father Thomas Jefferson, who had an intense interest in mastodons, proposed designating them as a symbol of American strength during the American Revolution,
In the mid to late 1800’s, mastodon bones and teeth were recovered in New Britain, Sharon, Bristol and Cheshire, Connecticut. In late August, 1913, a trench was being dug at the Hill-Stead Estate, near Farmington. Water was being redirected from a nearby swamp to a retention pond. At some point, a worker’s shovel struck what was at first believed to be a tree stump. It was then concluded that it might be a bone. Help was sought from Yale experts. As careful digging proceeded, more bones were recovered along with one of the creature’s tusks, located some 23 feet away from the original find. Believed to have died some 12,000 to 14,000 years earlier, it was the most complete skeleton of the extinct mammal unearthed in New England.
Long before Long Island Sound was a freshwater lake, dinosaurs roamed many parts of the globe. Dinosaur bones were uncovered in East Windsor, Connecticut during the early 1800’s. But, during the late summer of 1966, even more evidence of the giant reptiles’ existence in the state were discovered at Rocky Hill. As excavation was being conducted for the construction of a State Research and Testing Lab, bulldozer operator Edward McCarthy uncovered a slab of gray stone with strange-looking footprints imbedded in the stone. Yale’s Peabody Museum and University of Connecticut paleontologists were called in. They soon identified the footprints as those of dinosaurs, dating back as far as 200 million years. Barely one month later, the State’s governor announced that the area was to be preserved as the “Dinosaur State Park.”.
    Connecticut Glacial Lake was barely a microsecond hiccup in the earth’s history, yet it was vital in the formation of Long Island Sound. Adults and children can experience much of the earth’s past and present natural history, and the world’s beyond at New York’s American Museum of Natural History and Planetarium. At the Dinosaur State Park, along with its engaging exhibits and nature trails, the facility allows children and interested adults the opportunity to even make cast of real dinosaur footprints.  
In late December of 2019, Yale Peabody Museum’s Great Hall of Dinosaurs closed for renovation. The 200 million-dollar project is expected to take about 3 years. With the reopening of its exhibit hall, it will be yet another resource for learning more about the planet’s natural history.

Websites: American Museum of Natural History:   https://www.amnh.org
Connecticut Dinosaur State Park: https://www.dinosaurstatepark.org/
Yale Peabody Museum:     https://peabody.yale.edu/

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