(;EOLOGY. Massachusetts has a very complex geological history. At the beginning of Cambrian time three mountain masses of granitic rock ex tended across the State to the northeast, alter nating with arms of the sea. Cambrian and Ordovi cian strata were deposited on the shore of the Champlain channel, west of lloosoe Mountain; in a narrow gulf, which extended from Gaspe Point to Worcester; and in a trough extending from western Rhode Island via Portsmouth to Fundy Bay. The lloosae Mountain and its eon tinuation in the Green Mountains represent the axis of the Appalachian mountain-making in New England, and the older Paleozoic elastics to the west were very strongly metamorphosed— the limestones into marbles, the muds and gra vels into slates and schists, and some of the sandstones into quartzites. In Carboniferous time the whole State had been worn down to base level, and coal measures were deposited in the Rhode lsland-Nova Scotia basin. and in the Gaspe-Worcester trough. In Triassic time there was an estuary in the Connecticut River Valley extending to the northern boundary of the State, with an average of twenty miles in width. This
estuary was gradually tilled with sandstones; and during their formation there were great out flows of trap rock. In the later Cretaceous all New England was reduced to base level, the south eastern margin of Massachusetts being under a shallow sea, receiving deposits of clays, as at Gay's Bead, in Martha's Vineyard. The State was involved in the uplift of the Appalachian region at the close of the Cretaceous, and was raised into a plateau of moderate elevation. Massachusetts shared with the whole of New England in the denudation and erosion of the Pleistocene glaciation. The ice moved south ward and southeastward across the State, dis charging into the sea beyond Nantucket and Long Island. It strongly accentuated the southward trending valleys, while the higher ridges were denuded of soil, and the ice, on receding to the north, left the State strewn with a mantle of d rift.