ed
characteristic land forms, the migration and settlement of human beings,
the facility or difficulty of intelligent intercourse between races and
communities, with finally the commercial interchange of those
commodities produced by varying climatic conditions upon different parts
of the continental surface; in short, for those geographical factors
which form the chief product of past and present human history. (See
Geography.)

CONTINENTAL SHELF, the term in physical geography for the submerged
platform upon which a continent or island stands in relief. If a coin or
medal be partly sunk under water the image and superscription will stand
above water and represent a continent with adjacent islands; the sunken
part just submerged will represent the continental shelf and the edge of
the coin the boundary between it and the surrounding deep, called by
Professor H. K. H. Wagner the continental slope. If the lithosphere
surface be divided into three parts, namely, the continent heights, the
ocean depths, and the transitional area separating them, it will be
found that this transitional area is almost bisected by the coast-line,
that nearly one-half of it (10,000,000 sq. m.) lies under water less
than 100 fathoms deep, and the remainder 12,000,000 sq. m. is under 600
ft. in elevation. There are thus two continuous plain systems, one above
water and one under water, and the second of these is called the
continental shelf. It represents the area which would be added to the
land surface if the sea fell 600 ft. This shelf varies in width. Round
Africa--except to the south--and off the western coasts of America it
scarcely exists. It is wide under the British Islands and extends as a
continuous platform under the North Sea, down the English Channel to the
south of France; it unites Australia to New Guinea on the north and to
Tasmania on the south, connects the Malay Archipelago along the broad
shelf east of China with Japan, unites north-western America with Asia,
sweeps in a symmetrical curve outwards from north-eastern America
towards Greenland, curving downwards outside Newfoundland and holding
Hudson Bay in the centre of a shallow dish. In many places it represents
the land planed down by wave action to a plain of marine denudation,
where the waves have battered down the cliffs and dragged the material
under water. If there were no compensating action in the differential
movement of land and sea in the transitional area