The Appalachian Highlands, extending from Alabama to Newfoundland, include South-eastern Quebec. They reach their widest extent in the Eastern Townships and their greatest relief in Gaspé where the Shickshock Mountains have many summits above 3,500 feet.
The rocks here are different from those of the Laurentian Upland. They are mostly sediments of the Paleozoic Era, ranging from Cambrian to Carboniferous. The Cambrian rocks are mostly altered sediments: quartzites, argillites, schists and slates; the other formations contain limestones, sandstones and conglomerates as well as schists and slates. The strata have been folded, broken and crushed by mountain building. In the process igneous rocks were intruded. Bodies of serpentinized peridotite date from the earliest period; basalts, granites, diabases and syenites appeared later. The intrusive rocks are harder than the sediments and stand out now as the highest summits.
The Appalachians became ridges of high mountains during the latter part of the Paleozoic Era. Two chief periods of mountain-building are known: the Taconic revolution at the close of the Ordovician; and the Acadian during the Devonian; other disturbances occurred later. Then came cycles of erosion lasting for more than 200 million years, until glaciation happened here as in all other parts of the Province. So, it is no Surprise to find in the Appalachian Highlands a smooth relief of plateaus and deep valleys with only a few ridges.
The highest summits are seen in the Gaspé peninsula. Mount Jacques-Cartier, Quebec's highest peak, rises to 4,160 feet and is surrounded by twenty others ranging from 3,500 to 4,000 feet. Westward the serpentine mass of Mount Albert is 3,775 feet high, and southwestward the bold range of the Shickshocks stretches for 55 miles towards Matapedia valley. Its highest summits are: Logan (3,700′) Bayfield (3.470′), and Mattawa (3,370′). There is a great contrast in relief between the northern and southern shores of the peninsula. The first one is bold; in some places shore cliffs rise 800 to 1,000 feet; the other is low and irregular; the 1,000 foot contour lies some 25 miles away from the Chaleur shoreline.
Between the Matapedia and Chaudiere Valleys, very few summits rise above the old peneplain of 1,200 feet. Valley floors afford easy passages from the St. Lawrence estuary to New Brunswick. In the Eastern Townships the relief becomes bolder. From west to east, three parallel ranges are to be found: the Sutton range, extending from the Green mountains of Vermont into Canada, the Stoke range, from west side of lake Memphremagog to lake St. François and the Megantic range, close to the New Hampshire and Maine border. Amongst the highest summits are: Sutton (3,200′), Orford (2,860′), Chapman (1,800′), Gosford (3,875′) and Megantic (3,620′). Between the ridges, the deeply dissected plateaus seldom exceed 1,200 feet in altitude.
The Pleistocene glaciation is nearly as evident here as in the Laurentian plateau. Ice erosion has deepened the long lakes such as Memphremagog in the south; Temiscouata and Matapedia in the north. A mantle of glacial drift covers the underlying rocks. The rivers were ponded back of the glacial ridges forming high level lakes. The moraines have yielded better soils for agriculture than in the Laurentians, especially when buried by more recent clay and sand deposits.