Lake Hitchcock was a long, narrow glacial lake that filled the Connecticut River valley near the end of the last Ice Age after meltwater from the retreating Laurentide Ice Sheet was trapped behind a terminal moraine at present-day Rocky Hill, Connecticut. Stretching as much as 320 kilometers, or 200 miles, north to present-day St. Johnsbury, Vermont, it also helped redirect the Connecticut River southeast to its present outlet at Old Saybrook. Lasting about 3,000 years, the lake left annual sediment layers called varves that preserve a detailed record of postglacial environmental change and were later used by European settlers for brick-making. It was named for geologist Edward Hitchcock.