Coleman was an authority on glaciation, visiting and studying every known ancient and modern glacier.

Pleistocene glaciation of southern Ontario, especially around Toronto, was one of Coleman's favourite studies. He started publishing his opinions and results in 1887 and continued to deal with this subject for the next fifty years. Pleistocene geology of the Eastern Provinces provided another area of interest and led to sustained publication from 1916 to 1937.

Once retired, Coleman visited mountain systems throughout the world. This research resulted in the 1926 book, Ice Ages, Recent and Ancient and the posthumously published The Last Million Years (1941). He was active into his eighties making scientific expeditions to the Colombian Andes, to the mountains in Southern Mexico, and to mountains in Central America.

The details of A. P. Coleman's early twentieth-century scientific discoveries, theories and explanations have been further sharpened, often superseded, and sometimes abandoned in the more than half a century of work by thousands of researchers which followed. Nevertheless, Coleman in his "... search for high mountains" played an important historic role in laying a solid foundation upon which many generations of earth scientists were able to build and then to "search" for their high mountains.