This erratic boulder on top of a hill in Mansfield was photographed in 1902. Because the boulder lies on top of the hill, there is no higher place from which it could have rolled. Only the ice sheet, thousands of feet thick, could have left this boulder on such high ground.

look like the kind of stuff flowing water leaves behind. Many deposits covering the bedrock were found to be completely unsorted by grain size, or at best only slightly sorted. (These are the deposits we now call till.) Such confused deposits could not be the product of flowing water, the great sorter of sediment. Plainly, the Noachian theory did not explain away all the problems of surficial geology.

In 1825, one Peter Dobson of Vernon, Connecticut, was supervising the construction of a cotton mill when he became puzzled by the rounded boulders randomly mixed in with sand and clay (till, again) that his workmen kept digging up. He proposed an explanation that was published the next year in Silliman's American Journal of Science. Dobson wrote, "I think we cannot account for these appearances unless we call in the aid of ice along with water and that they [the boulders] have been worn by being suspended and carried in ice, over rocks and earth, under water."" This was the first theory published anywhere that suggested erosion and transportation by ice might in some way be

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