THE LAxns. There is a eonflict of forces at the present time operating to modify the forms of the lands whWb themselves so greatly influence life. On the one hand contraction id the inte rior of the earth is eausing changes in the level of the eruct as a result of which continents are raised and (wean bottoms depre—ed. while moun tain chains, volcanoes. plateaus, and plains are being made. (in the other hand opposing forces are at work on the land removing the rocks that lie above the sea level and dragging the fragments into the :ea. The weather disintegrates the rocks, the rains. rivers, and winds remove the frag ments. I:laeier- occasionally aid in this erosion, and the seacoast is the seat of farther important work of this kind. The result of the opposing forces of elevation and destruction has been to produce a very complex land surface. and it is one of tuiyt important provinces of 'thy-Mora phy to understand thin lantl surface and to (mint out its effect on life. For this phase of physi ography the name geomorphology has been pro posed. It is intimately related to geology use of geological principles. It is by some eon-idered as a branch of geology; that is, the geology of the present.
Many of the principles to the physi ography of the lands are stated under other topics.
(See nivER; LAKE: ..NIOUNTAI etc.) In this place only the scope of the subject will be indi cated. The simplest land form is the plain (q.v.), the most extensive and perfect plains be ing on the sea bottom. They may be elas:ified as constructional and destruetional, the former be ing represented by elevated sea-bottom plains, lake-bottom plains, delta plains, flood-plains, etc.; the latter by plains of marine denudation, plains caused by lateral erosion of rivers, etc. In the beginning their surfaces are level. they permit the ready spread of animals and plants, and. if the climate favors, they are usually well suited to occupation by man. if newly formed, or young, the surface may be so level that water stands on it as lakes or swamps; but with in creasing age the surface is drained. streams cut valleys, the flat-topped divides are narrowed, and the lakes and swamps are destroyed. In the devel opment of these stream valley:, if the plain stands high enough above sea level. or base level, the rapid cutting along the channels permits the de velopment of deep, steep-sided valleys. In these young valleys the vigorously working streams flow with rapid slope. and with occasional falls where hard layers are encountered. If the land is high above base level, that is. if it is a plateau, the young streams may so trench the land that travel across country is prohibited by the deep callous. In such cases the interstream areas only are habitable and are chosen for roads and railways. With time the valleys broaden. the slopes become more gentle. and both the valley bottoms and sides invite settlement. Such a land surface is mature, and is well illustrated by the Mississippi Valley. There are few if any falls.,
the river, are navigable. and they are bordered by flood plains—waste from the land along the course which the river i- unable to bear to the sea over its gentle lower slope.
The Alps as a barrier to the spread of life. and as a refuge from invasion, stand as rugged moun tains reaching above the snow line. Their rug gedness is due to their youth and to the fact that denudation, working high above base level, on rocks of very different degrees of hardness. has been able to work rapidly and sear and carve the mountains profoundly. With greater age moun tain peak, and ridges are lowered, the valleys are broadened. and the rivers slowly shift position, eating their way backward at the headwaters. rob bing weaker opponents of drainage area, and push ing their way across ridge after ridge. as in the Appalachians. The importance of the river gaps to transportation and the influence of mountains on occupation are observable throughout the world.
Rising land gives a straight coast, as along Western South America; sinking forms an irregu lar coast. with many islands, peninsulas, har bors, and straits, as in the 'Northeastern United States. A shelving coast of soft materials which has recently assumed its position is skirted by sandbars. like the coast south of New York. while a young coast of hard roek has bold head lands, with beaches in the bays. Here again are innumerable opportunities to study land forms in order to understand their cause and point out their influence on life.
The physiography of the lands investigates isl ands, peninsulas, capes. plains. plateaus, and val leys: it studies their differences in form; it dis tinguishes between the different kinds of hills.
cliffs, talus slopes, etc. In fact, it studies all land features, and in all cases it is concerned with the form. its cause, its relation to other land forms, and its effects on life. It shows how, in their conflict. the movements of the crust and the operation of the agents of denudation make land forms by constructional and by destructional processes. It shows that there is a constant building up of land forms by both the internal forces of elevation and the external forces of denudation; and that there is constant tearing clown by the force. of denudation. It is the province of physiography to trace the operation of these processes. both to see how they modify the lands and to discover the influences of these modifications on life.
BIBLIOGRAPHY. Powell. Stealer, etc., PhysiogBibliography. Powell. Stealer, etc., Physiog- raphy of the United N fates (National Geographic Society Monograph. Washington. 1896) ; Huxley, Physiography (London, 1SSO) ; Alackinder, Brit ain and the British Seas (New York, 1902) ; Tarr, Physical Geography of New York State (ib., 1901) ; id., New Physical Geography (ib., 1897) ; Davis. Physical Geography ( Boston, 1900) ; Stealer. Nature and Man in America New York, 18971; id.. Sea and Land (ib., 1890. See GEOLOGY; GEOGRAPHY. etc.