In 1848, the bones of a woolly mammoth (Mammuthus primigenius) were uncovered in Mount Holly, Vermont, during excavation for the first railroad tracks across the Green Mountains. While these bones offer dramatic evidence of the ice ages that once scoured New England, they are by no means the only evidence. The testimony of ice is everywhere.
Twenty thousand years ago, a continental glacier flowed from Hudson Bay south over all of New England. This was only the last of many glaciers to visit the region over the preceding 1.8 million years. This ice scraped, smeared, smothered, and bulldozed the entire region. Eventually the climate started to warm, the glacier stalled, and, in the manner of a giant conveyer belt, deposited the enormous piles of rubble we call Cape Cod and Long Island.
This continental glacier was over a mile thick and overtopped the highest peaks of the Green and White mountains. The slowly moving ice carved a gradual ramp up the northern slopes of mountains. In contrast, on the southern faces, the moving ice plucked away the bedrock to form cliffs. Camel’s Hump in Vermont offers a dramatic example of this plucking.
The moving ice also chiseled out flat-bottomed, steep-sided, U-shaped valleys where it flowed southward. The ice seems only momentarily departed from the flats along Route 4 in Killington, Vermont, or along Route 302 in Crawford Notch, New Hampshire.
Around 11,000 years ago, the continental glacier finished the slow process of melting out of New Hampshire and Vermont. Alpine glaciers continued on to further etch Tuckerman’s Ravine on Mount Washington and similar, steeply rounded valleys or cirques. On Mount Equinox in Vermont, there are potholes scoured into the bedrock by swirling melt-water and gravel. These potholes are curiously perched on the edge of a cliff, next to where a melting lobe of ice once held the water against the bedrock.
Now-vanished ice is also responsible for the geological features called kame terraces, which are found up and down the Connecticut valley. Gravel, sand, and boulders slumped off the emerging hillsides and piled up along the margins of the last tongue of ice that remained in the bottom of the valley. As the tongue continued to melt, these deposits were left behind as flat terraces, high above today’s river level.
As the melting progressed, cracks in the rotting glacier filled with melt-water. These cracks developed into rivers within the ice, which then created their own sand and gravel bottoms. When the glacier finished melting, these gravel ribbons, known as eskers, were left behind as steep ridges of sand and gravel, some more than 100 feet tall. The esker in the Connecticut River valley that runs between Hanover, New Hampshire, and Bradford, Vermont, is particularly prominent.
As the last ice melted, the Connecticut River valley flooded under a deep lake that was dammed up behind a debris pile in Rocky Hill, Connecticut. Later named Lake Hitchcock, the body of water eventually backed up all the way to the First Connecticut Lake, near the Canadian border. The lake also extended far west up the White River valley. Ice in western Vermont created a dam in the Winooski watershed. The resulting Lake Winooski drained south through Granville Notch to enter Lake Hitchcock in North Randolph, Vermont.
Along the larger brooks and tributaries that fed Lake Hitchcock, you now find sand and gravel quarries. The fast water of these brooks pushed small rocks and gravel to the edge of the lake, and a little farther into the quiet water, they deposited the finer sand. The St. Pierre quarry near Ox Brook in Charlestown, New Hampshire, is a perfect example. In some sections of the quarry, small pockets of clay are also found; clay settles out of suspension very slowly, only in the calmest of waters. In nearby Rockingham, Vermont, layers of clay and silt reveal the alternating seasons of quiet under winter’s ice with the renewed runoff of summer silt.
Life returned to Vermont and New Hampshire in the immediate wake of the glacier, colonizing the rocks, sand, gravel, and silt that covered the dry land. Lichens such as reindeer moss were first on the barren lands, followed by tundra and spruce trees. Giant sloths, horses, mastodons, and predators such as the short-faced bear soon thrived. The first human arrivals followed the megafauna into the valley around 11,000 years ago. At that time, Lake Hitchcock still filled the Connecticut Valley north to the retreating glacial margin at Littleton, New Hampshire.
The remains of the Mount Holly mammoth included vertebrae, a seven-pound, sedge-grinding molar, and a tusk. In 1865, another 40-inch mammoth tusk was recovered from a similar peat deposit in Brattleboro. These ancient teeth recall the time when Vermont and New Hampshire were freshly ice-shaped lands.
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