A Connecticut Department of Energy & Environmental Protection and University of Connecticut Partnership
Geological > Geology of Long Island Sound
Figure 5:  26,000 - 21,500 Years Ago
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A View of Connecticut and a Portion of the Atlantic Coastal Plain at the Height of the Last Glaciation, About 21,000 Radiocarbon Years Ago

Tills associated with two Pleistocene glaciations have been found in Connecticut and as far south as Montauk Point on Long Island. Not much is known about the first glaciation, which is thought to have occurred in Illinoian time (about 150,000 years ago). The second glaciation, which is depicted here, occurred in Wisconsinan time. This glacier advanced into Connecticut about 26,000 radiocarbon years ago, reached its terminal (southernmost) position on Long Island about 21,000 radiocarbon years ago, and had melted out of the state by about 15,000 radiocarbon years ago. When the Wisconsinan glacier was at its maximum, sea level was about 300 feet lower than it is today.

The pre-glacial topography of the region was altered but not completely changed by these ice advances. On Long Island, prominent east-west trending moraine ridges mark the southernmost advance of the last glacier (shown here), and a melt back (recessional) position along the north shore. The basin that Long Island Sound now occupies was smoothed but aspects of its stream-cut character can still be detected. Further to the north, pre-existing bedrock hills were rounded and valleys were widened and deepened but the overall north-south grain of the land was not materially changed.

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