Thousands of years ago New England was blanketed by a great sheet of packed snow and ice. The ice pack moved slowly across the landscape, sometimes advancing, sometimes retreating. More than a mile thick, it flowed across even the highest mountains in a generally southeasterly course. As the ice passed over rock outcroppings, blocks of otherwise resistant material, were broken from the parent rock along naturally occurring fracture lines. Usually the fragments were carried only a short distance allowing their source to be easily traced.

The great glacial boulders we find when rambling across New England's countryside are an integral part of our history, past and present. Other signs also reflect and illuminate our glacial past. The swamps and bogs that formed in unsorted glacial debris, U-shaped valleys like the Pinkham, Crawford and Franconia Notches carved by glacial ice, precipitous waterfalls, striated rocks scraped by rock fragments packed in ice, and even our soils, owe their origin to glacial action.