"When the expanse of more recently formed land on which Nantucket stood was submerged, Nantucket was insulated by the advance of the sea around it, and the other islands in the same chain—, , , and s—were similarly left standing in the ocean. Nantucket was, therefore, a —a halting-place of the glacial movement,—that is,it was formed by the advancing lower rim of the glacier which, melting, deposited its accumulation of —sand, clay, and s—caught up in its southward march, and frozen within its substance, in great heaps where they exist to-day as islands in the ocean."