Newfoundland is surrounded by shallow seas covering the great submerged continental shelf of eastern North America. The 100 fathoms contour is usually considered to mark the shoulder of the slope which leads to the ocean depths. Across this shelf there are a number of deep valleys, particularly the one which lies between Nova Scotia and Newfoundland and leads toward the mouth of the St. Lawrence River. It is apparent that the island is only the more elevated undrowned portion of a great eastern continuation of the mainland of North America. The "Banks" are the more elevated portions of this submerged plateau; the most noted of these, the "Grand Banks", lying southeast of Newfoundland, have an area as great as that of the island itself.
The shallow waters of the Banks are located in the area where the warm Gulf stream is met by the cold Labrador current. The continuous mixing which takes place creates conditions of temperature, salinity and nutrient supply which are most favourable to the development of the small floating plants upon which the food supply of the fish population ultimately depends. Consequently the Banks, have, since their discovery, continued to be one of the greatest fishing grounds in the world.
Although the island might for the sake of simplicity be regarded as a plateau sloping gently in a northeasterly direction it is divided naturally into three physiographic units; the Western Uplands, the Central Plateau and the Avalon Peninsula.
The Western Uplands
The Long Range Plateau includes the northern peninsula of Newfoundland which extends unbroken from Bonne Bay to the Strait of Belle Isle, together with the more isolated highland masses extending southward from Bonne Bay to St. Georges Bay. It is separated from the rest of the island by a down-faulted lowland, marked by St. Georges Bay, Grand Lake and White Bay. The summits of the Long Range are found along the western margin of the Upland, below which a steep escarpment falls to a narrow coastal plain along the Gulf of St. Lawrence. Gros Morne, 2,651 feet above sea level, overlooking Bonne Bay and the isolated Lewis Hills, 2,763 feet, are the highest points on the island. A steep scarp marks the eastern border of the plateau, especially along White Bay where rocky cliffs 300 to 500 feet high overlook the sea. The Anguille Mountains, flat topped uplands whose highest point is 1,759 feet above sea level, overlook St. Georges Bay from the Southeast. On the east of these hills lies the Codroy Valley, bordered by steep escarpments. It merges northward with the coastal plain of St. Georges Bay.
The Central Plateau
The western edge of the central plateau is a more or less continuous escarpment overlooking the downfaulted lowlands which extend from the Codroy Valley to White Bay. Composed of more resistant rocks, this part of the plateau has summits over 2,000 feet, constituting the Southern Long Range. East of the valley of the Exploits River the Annieopsquotch Mountains also have summits about 2,000 feet in elevation. The general level of the plateau, however, is about 1,000 feet, with a barren rocky surface marked by innumerable lakes and bogs. The southern margin of the plateau is steep and fairly regular, suggesting that it also is a fault zone. From the south and west the surface slopes gently toward the northeast where it dips below sea level. In Bonavista Bay and Notre Dame Bay particularly, there are a great number of islands and indentations corresponding to the irregularities of the old peneplain surface.
Almost separated from the main body of the island by Trinity Bay and Placentia Bay, the Avalon Peninsula is essentially part of the same plateau. Its outline is very irregular with deep bays separating the peninsulas. The surface is generally between 500 and 1,000 feet in elevation and very rocky and barren.