The Story of Central Massachusetts
The protracted story of central Massachusetts might be that of many another section of eastern North America, except for minor details. In Cambrian time an inland sea, well stocked with simple marine organisms, washed the shores of an archipelago which extended north and south through the Berkshire Hills, the Green Mountains, and the Notre Dame Mountains. Composed of rocks which themselves had had a long and involved geological past, the islands rose intermittently as streams and waves wore them away. Clear water and sandy beaches stretched along their western shore, and the original Adirondack Mountains were just visible from the summits of the higher islands. Swift streams raced down their eastern slopes, carrying gravels, sands, and silts into the eastern arm of the sea, and only free-swimming animals could survive in its turbid waters. For a time, volcanoes erupted and fumed along the entire eastern coast from Thetford Mines, Quebec, to Plainfield, Massachusetts, but their activity was short-lived. Only the streams which drained the broad islands endured, and they never ceased to pour mud into the eastern ocean. Gaps in the island chain permitted some of the free-swimming organisms to migrate to the western sea, where bottom-living plants and animals were actively secreting the limy shells and skeletons which helped build thick deposits of Cambrian limestone.
These conditions continued into the ensuing Ordovician period of geologic time, but gradually the situation changed. Again the volcanoes renewed their activity, and masses of dark peridotite were intruded along the eastern shore; the island chain rose rapidly, and the straits closed. The elevated land began to expand outward, and folds spread eastward on the east and westward on the west, like waves from a center of disturbance. So great was the pressure that portions of the old land were sheared outward over the folded sediments. The Taconic disturbance was on from the city of Quebec to the city of Washington; and the streams, like ants, kept at their endless task of carrying sand and gravel into any and every depression they could find. They piled up great thicknesses of Silurian sandstone in Maine and New York, and so effectively did they tear down the Taconic Mountains that the Silurian sea was ultimately able to penetrate the region from Thetford Mines, Quebec, almost to White River Junction on the Connecticut River.
Fig. 13. Block diagram showing main features of central New England during middle Ordovician time.
Fig. 14. Block diagram showing main features of central New England at the end of Ordovician time.
Fig. 15. Block diagram showing main features of central New England during the Devonian period.
One period later a Devonian sea followed in the wake of the Silurian sea, but its waters penetrated even farther south to Leverett, Massachusetts. The quartz gravels of its advancing beach covered the worn flanks of the Taconic folds. Sea animals left their shells to form a bed of limestone which may be seen today at Bernardston. But again the sea was shouldered aside by the restive land, which rose from Gaspé to Virginia. Much of the region affected by the Taconic disturbance was elevated again, and a broad band of Devonian sediments was folded closely through northern New Brunswick, southern Quebec, northern Maine, northern and central New Hampshire, and central Massachusetts. Granites welled up into the sediments, and dikes filled all the fissures. The baking, stewing, and reinforcing they gave to the older sediments made them so firm that they are still one of the most coherent and resistant series of rocks in New England and maritime Canada. This was the Shickshock or Acadian disturbance. Meanwhile the first forests took root on the long piedmont plains that spread from the rising mountains westward into the Catskill Plateau of New York State (Catskill sandstone) and eastward to the coast of Maine (Perry formation).