One of Coleman's lifelong driving interests was the study and understanding of glaciations throughout the earth's history. His work on the Pleistocene of Southern Ontario led him to interpret the interglacial scene. Coleman was able to peek into the past before human habitation, in the Don Valley in Toronto.

.. . one can see the ancient forest of maples and oaks and many other trees on the river shore with deer coming down to drink, bears tearing open a rotten log for its small inhabitants; and at some creek mouth the giant beaver fells a tree with a splash to feed on its branches; while openings in the forest show buffalo grazing. A thunder-storm comes up, lightning strikes a blasted tree, and fire runs along the river bank, stampeding the forest dwellers which rush to the water for safety -all recorded with many more features not referred to in the sand and clay beds between two sheets of [glacial] boulder clay. ..

A. P. Coleman. The Last Million Years: a History of the Pleistocene in North America. Toronto:
University of Toronto Press, 1941: 76 – 77