Set a geol­o­gist down any­where in New Eng­land and some­where near­by he will show you the work of ice. Eigh­teen thou­sand years ago all of New Eng­land lay beneath a half-mile-thick sheet of ice, part of a con­ti­nent-span­ning glac­i­er that reached from the deeply indent­ed coast of the Pacif­ic North­west to the gen­tly slop­ing con­ti­nen­tal shelf of New England.