The continental shelves are parts of the great continental blocks which have been covered by the sea in comparatively recent times, and their surface consequently presents many similarities to that of the land, modified of course by the destructive and constructive work of the waters.
The continental shelves include not only the oceanic border of the continents but also great areas of the enclosed seas and particularly of the fringing seas, the origin of which through secular subsidence is often very clearly apparent, as for instance in the North Sea and the tract lying off the mouth of the English Channel.
As so defined the hemipelagic deposits are those which occur in general on the slope from the continental shelves to the ocean depths and also in the deep basins of enclosed and fringing seas.
Glacial detritus naturally plays a great part in the deposits on the polar continental shelves.
In the Atlantic it is the characteristic deposit of the slopes of continental shelves of western Europe and of New England, being largely mixed with ice-borne material to the south of Newfoundland.