Geological and geophysical investigations of the Gulf of Maine and surrounding land areas reveal the presence of a major rift system landward of the continental slope. This rift system is part of a linear fracture belt which developed along the eastern margin of the North American continent in the late Paleozoic and early Mesozoic as the Atlantic Ocean began to open. Rifting began in the Late Devonian along a nearly continuous belt between southeastern New England and the Grand Banks. Tensional movements were re-initiated in the Late Triassic following a period of quiescence between the Late Pennsylvanian and early Mesozoic. This latter rifting not only occurred within the late Paleozoic rift belt, but also along the North American continent from Newfoundland to Florida. Tensional fracturing continued into the Early Jurassic and was accompanied by translation of crustal blocks eastward. This final phase of rifting probably ended when the igneous body causing the east coast magnetic anomaly was intruded along the continental slope and the continent became coupled to the spreading North Atlantic sea floor.