It has been emphasized that the uplands are all underlain by hard crystalline rocks. The lowlands, on the other hand, are found on the weaker sandstones, shales and limestones; sedimentaries in large part belonging to the Carboniferous system.
The Chaleur Bay region was a basin of deposition as far back as Devonian and Carboniferous times. The present lowland, developed on these rocks, consists of a narrow coastal strip both north and south of the Bay.
The Maritime Basin
The central feature of the structure of the Maritime Provinces is, of course, the broad syncline or depositional basin in which the great areas of Carboniferous or coal-bearing rocks were laid down. It underlies the whole southwestern part of the Gulf of St. Lawrence as well as the whole of the Province of Prince Edward Island, nearly one half the area of New Brunswick, and the Northumberland Coastal Lowlands of Nova Scotia. The most prevalent rocks in the Central and Eastern Lowlands of New Brunswick are the Millstone Grits, sterile sandstones of the Pennsylvanian or Upper Carboniferous system. Coal is found in the central portion near Minto, and a few thin seams are also known along the shore of Chaleur Bay. Much of the area is flat and swampy, the drainage having been deranged by glaciation. Much of the plain is covered with deep sandy drift, but in places the rock lies almost at the surface over broad areas. In general, the plain is below 500 feet A. T., but around the edges of the basin the limestones of the Lower Carboniferous system come to the surface in ranges of rocky hills, 500-600 feet A. T. More or less to be considered an outlier of this system, is the Petitcodiac-Kennebecasis valley carved in Carboniferous rocks preserved in the syncline between the Kingston Hills and the Southern Uplands. The eastern end is floored by Pennsylvanian sandstones while the western end is underlain by Mississippian limestones.
The North Shore or Northumberland Coastal Lowland of Nova Scotia is the eastward extension of the Carboniferous lowland of New Brunswick. Here, however, the beds are of slightly different character. While the Millstone Grits still appear in the crests of the long low anticlines, which cross the country in a direction slightly north of east, the coal measures occupy the synclines, giving rise to the productive mines at Joggins, Springhill and Stellarton. Gypsum, salt and oil shales are found in the Windsor beds of the Carboniferous system. By far the greatest area, however, is underlain by the red beds of Permian age which characterize the northern part of the coastal plain and the whole of Prince Edward Island where boreholes have proven them to be more than 2,000 feet thick.
The Antigonish-Guysborough Lowland is also underlain by Pennsylvanian or Upper Carboniferous rocks, mainly sandstones, shales and conglomerates. In the lowest part of this basin around Antigonish, however, are found the Windsor beds containing limestones and gypsum.
Cape Breton Lowlands, involving almost half the area of the island, are also developed upon Carboniferous rocks, both the sandstones and the gypsum-bearing limestone beds being in evidence. The coal measures are preserved only in broad, pitching synclines with outcrops near the shore in the Port Hood, Inverness and Sydney areas so that the greater part of the coal reserve lies beneath the sea.
The last system of lowlands, with which we must deal, is that connected with the Bay of Fundy and its head waters. Here again, we have a great syncline in which are preserved rocks of Triassic age, the youngest rocks in Eastern Canada. While the outcrop of Triassic lava stands out as the North Mountain ridge, the underlying red shales and sandstones are eroded to form the Annapolis-Cornwallis Valley, Annapolis Basin and St. Mary's Bay. This long lowland is generally known as the Annapolis Valley. Further east the syncline contains Minas Basin and the red sandstones outcrop around the shores of Cobequid Bay. The greater part of the Hants-Colchester Lowland, however, is developed upon rocks of Carboniferous age, the limestone and gypsum beds in the vicinity of Windsor being extensively worked.