CONTINENT (from

See also:

• LAT

Lat. continere, "to hold together "; hence " connected," " continuous ")  , a word used in physical geography of the larger continuous masses of land in contrast to the great oceans, and as distinct from the submerged tracts where only the higher parts appear above the sea, and from islands generally . On looking at a map of the world, continents appear generally as wedge-shaped tracts pointing southward, while the oceans have a polygonal shape . Eurasia is in some sense an exception, but all the southern terminations of the continents advance into the sea in the form of a wedge—South America, South Africa, Arabia, India, Malaysia and Australia connected by a submarine platform with Tasmania . It is difficult not to believe that these remarkable characters have some relation to the structure of the great globe-mass, and according to T . C . Chamberlin and R . D . Salisbury, in their Geology (1906), " the true conception is perhaps that the ocean basins and continental platforms are but the surface forms of great segments of the lithosphere, all of which crowd towards the centre, the stronger and heavier—the ocean basins—taking precedence and squeezing the weaker and lighter ones—the continents—between them." " The area of the most depressed, or master segments, is almost exactly twice that of the protruding or squeezed ones . This estimate includes in the latter about To,000,000 sq. m. now covered with shallow water . The volume of the hydrosphere is a little too great for the true basins, and it runs over, covering the borders of the continents" (see CONTINENTAL SHELF) . Several theories have been advanced to account for the roughly triangular shape of the continents, but that. presenting the least difficulty is the one expressed above, "since in a spherical surface divided into larger and smaller segments the major part should be polygonal,while the minor residual segments are more likely to be triangular." As bearing on this geological idea, it is interesting to notice in this connexion 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 Too to 300 M. broad, of which the Challenger Deep (11,400 ft.) and the great Tuscarora Deep are fragments . If on a map of the world a broad inked brush be swept seawards round Africa, passing into the Mediterranean, round North and South America, round India, then continuously south of Java and round Australia south of Tasmania and northward to the tropic, this broad band will represent the encircling ribbon-like " deep," which gives strength to the suggestion that the continents in their main features are permanent forms and that their structural connexion with the oceans is not temporary and accidental .

The great protruding or " squeezed " segments are the

Eurasian (with an area roughly of twenty-four, 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 sum of these will represent one-third of the earth's surface, while the remaining two-thirds is covered by the ocean . The foundation structure of the continents is everywhere similar . Their resulting rocks and soils are due to differential minor movements in the past, by which deposits of varying character were produced . These movements, taking place periodically and followed by long periods of rest, produce continued stability for the development and migration of forms of life, the grading of rivers, the development of varied 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 .