The great Northwestern Plateau of New Brunswick with a general level of about 1,000-1,500 feet above tide, is developed upon the folded calcareous or lime-containing slates of the Devonian period, and is part of an even larger region including much of the adjoining portions of Quebec and Maine. The area is deeply dissected by valleys tributary to both the St. John and Restigouche rivers.
The Central Highlands of New Brunswick consist of a dissected plateau having a skyline at above 2,000 feet A.T., surmounted by numerous monadnocks or relic mountains, the highest of which is Mount Carleton (2,700′). Numerous river valleys have deeply' trenched the plateau to a depth of 1,000 feet or more below the summit level. The underlying rock of this highland area is an immense granite mass or batholith which was intruded into the stratified rocks in Devonian times. Hardened and folded sedimentary rocks around the edges of the batholith also take part in the formation of the plateau.
The Central or York Plateau laps around the southern and eastern edges of the highland. Its elevation averages about 1,000 feet A.T. and it is developed in part on the Devonian granite batholith and in part on hard metamorphosed Paleozoic sedimentaries. The Saint John River cuts directly across it from west to east in a rather deep and narrow valley to debouch on the Central Lowlands.
The Southern Uplands of New Brunswick are made up of several widely separated areas. Largest and highest of these is the great upland ridge along the Bay of Fundy east of the St. John River, comprising the Caledonia Hills, the Kent Hills, etc., with a maximum elevation of about 1,400 feet A.T. In structure it is a long oval dome or arched ridge, with a core of PreCambrian volcanic and intrusive rocks, pitching toward the northeast where it is overlapped by a fringe of the Lower Carboniferous system containing oil shales. To the north, across the Kennebecasis valley, is the long low ridge of the Kingston Hills, also with a Precambrian core which is exposed toward the west but covered by Carboniferous limestones and sandstones toward the northeast. Another narrow longitudinal valley intervenes between the Kingston Ridge and the Belle Isle Ridge to the north. Here the hard Precambrian outcrops give rise to numerous rounded summits, among these Bull Moose Hill is about 800 feet A.T. West of the St. John River lies another rugged area formed partly upon similar hard ancient rocks and partly upon another immense granite batholith of Devonian age. Although much of this area is below 500 feet A.T., large areas are above 1,000 feet in elevation, Mt. Champlain in the Nerepis Hills being 1,462 feet A.T. and Mt. Pleasant, thirty miles further west, is 1,175 feet A.T.
The Cobequid Mountains in Nova Scotia, although appearing as a sharp ridge from both north and south, in reality form a plateau with a skyline at about 900 feet A.T., on top of which rest a few low rounded remnants from 100 to 200 feet higher. This upland, which is from 8 to 12 miles wide and eighty-five miles long, is underlain by a complex of igneous and altered sedimentary rocks ranging in age from Precambrian to Devonian.
The Pictou-Antigonish uplands extend completely across both counties--from eastern Colchester to Cape George. They also are developed upon hard old rocks-Precambrian and older Paleozoic, igneous and metamorphic--and in part upon hard sandstones of the Carboniferous system. The highest point, McNeil Mountain (1,010 feet A.T.), is a volcanic plug.
The North Mountain which separates the Bay of Fundy from the Annapolis Valley is an inclined sheet of lava or trap rock, dipping northwestward beneath the Bay in a dish-like fold. Seen from the south it presents a long, steep escarpment, the top of which has an elevation of 500700 feet A. T.
The Atlantic Upland comprises more than half the area of the Nova Scotia mainland. It also is an inclined surface rising northward at the rate of about 15 feet per mile to the brow of the South Mountain -- a northfacing escarpment (600-700 feet A. T.) overlooking the Annapolis Valley. The surface is extremely irregular, yet the skyline is flat except for a few residual hills or monadnocks a hundred feet above the general level. In the eastern part of the mainland the upland ends in an abrupt escarpment overlooking the valley of the St. Mary's River. The highest parts of this upland are developed upon enormous granite batholiths of Devonian age, while between them and the Atlantic Ocean the country is underlain by Precambrian rocks, -- the folded slates and quartzites (whin) of the Gold Bearing Measures. The latter, having been strongly folded, are exposed in long narrow alternate belts parallel with the main axis of the province. Drainage is immature in the interior but the valleys become deeper and better developed southward although the mouths of all the rivers are drowned.
On Cape Breton Island there are several upland ridges trending from southwest to northeast, all on hard Precambrian crystalline rocks. The Southeastern Upland rises gradually from the water's edge to an elevation of about 400 feet on the brow of the escarpment overlooking Salmon River. The East Bay Hills and Sporting Mountain are from 500 to 600 A. T. The North Mountains, Boisdale and Coxheath Hills are from 600 to 700 feet A. T. Further northward the Craignish Hills, Kelly Mountains and Mabou Highlands are all more than 1,000 feet high.
The Northern Tableland, much of which is now included in the Cape Breton National Park rises abruptly from the narrow coastal lowlands to an elevation of 1,200 feet A.T., and reaches 1,500-1,700 feet A.T. in the interior. Poor drainage characterizes much of the upland surface but the edges of the plateau are scarred by deep V-shaped valleys.