Continent

CONTINENT, a term used in physical ,geography for the larger continuous masses of land, namely: Asia, Africa, North America, South America, Europe and Australia in the order of their .size. See CONTINENTS, ORIGIN OF ; CONTINENTAL SHELF.

It

is interesting to take into consideration that the areas of volcanic activity are mostly where continent and ocean meet; and that around the continents there is an almost continuous "deep" from ioo to 3oom. broad, of which the Challenger Deep (I i,400ft.) and the great Tuscarori Deep are fragments. The great floating segments are the Eurasian (with an area roughly of 24, reckoning in millions of square miles), strongly ridged on the south and east, and relatively flat on the north-west ; the African (twelve) rather strongly ridged on the east, less abruptly on the west and north; the North American (ten), strongly ridged on the west, more gently on the east, and relatively flat on the north and in the interior; the South American (nine), strongly ridged on the west and somewhat on the north-east and south-east, leaving ten for the smaller blocks. The delicate balance or isostasy of lighter land material and heavier ocean-bed substance was made the subject of considerable work by Hayford The Figure of the Earth and Isostasy (1909) and a statement of modern views on the subject was made by A. Morley Davies in the Geographical Journal (July 1925).

The foundation structures of the continents are similar. Their rocks and soils are due to differential minor movements in the past, by which various deposits were produced. These move ments, followed by long periods of rest, allow of the development and migration of forms of life, the development of varied char acteristic land forms, the migration and settlement of human beings and intercourse between races and communities, with finally the commercial interchange of commodities produced upon different parts of the continental surface by varying soil and climatic conditions; in short, for those geographical factors which form the chief influences upon past and present human history. That such movements have not ceased is known by the fact that certain coastal regions are now undergoing changes of level by which land is emerging from the sea, or sinking beneath it. Such changes take place very slowly. There is general agreement that the positions of the present continents were determined as long ago as Archaean times. (See GEOGRAPHY.)