Whereas formation of the Isthmus of Panama marks the beginning of the Pleistocene epoch (3 MYA), the receding glaciers some 12,000 years ago mark its end. Just before it’s end, around 15,000 years ago, the glacial lake Hitchcock extended from beyond Hartford to St. Johnsbury VT. Having mapped river deltas that trace their flow into Lake Hitchcock, geologists have charted the lakes shore elevation to 300 feet above sea level (corresponds to the present elevation of Eaglebrook School that lies tucked into the Pocumtuck ridge, just east of DA). 15,000 years ago, Deerfield Academy was under water on what would have been the bottom of the lake, hypothetically shown in upper right image (Little and Sillin). Under 150 feet of icy, muddy, Lake Hitchcock water, the soils of present day Deerfield valley remained that way, underwater, against the backdrop of glaciers, for more than a thousand years.
From a human perspective, by 15,000 years ago hunter-gatherers are thought to have passed over the Bering Land Bridge and had become well settled in North America. As the glacial period continued, humans are thought to have passed from North America across the Isthmus of Panama and ventured into South America.
By 8000 years ago, with glaciers retreating, humans migrated back into the northeast and followed their icy retreat venturing north up into Canada, the Arctic Circle and then Greenland.
Richard Little speculates that glacial retreat (technically post glacial crustal rebound) may account for why the Deerfield River unexpectedly flows north in the rift whereas it’s master, the Connecticut River flows south. The image lower left (Little and Sillin) takes a southerly view through the present day Deerfield valley. Crustal rebound says, as the weight of a glacier compressed land underneath by hundreds of feet, more southerly regions would have had the glacial force removed first, given their northerly retreat. From this reasoning, southerly landscapes would be subject to rebounding before northerly landscapes. Moreover, Deerfield river water entering the rift would flow downhill in a north direction where it’s flow eventually met with the Connecticut River.
And what effect was the isthmus of Panama having on human travels during these corresponding times? 