No survey of the geological workings of plant and animal life upon the surface of the globe is complete which does not take account of the Influence of man--an influence of enormous and increasing consequence in physical geography, for man has introduced what seems superficially an element of antagonism to nature. Not content with gather ing the fruits and capturing the animals which nature has offered for his sustenance, he has, with advancing civilization, engaged in a contest to subdue the earth and possess it. His warfare, indeed, has often been a blind one, successful for the moment, but leading to sure and sad disaster. He has, for instance, stripped the forests from many a region of bill and mountain, gaining his immediate object in the possession of their stores of timber, but exposing the slopes to parching droughts or fierce rains. Countries once rich in beauty and plenteous in all that was needful for his support, are now burnt and barren, or washed bare of their soil. But now when that truth is coming more and more to be recognized and acted on, man's influence is none the less marked. His object is still to subdue the earth; and he attains it, not by setting nature and her laws at defiance, but by enlisting her in his service. The action of man may be witnessed on climate, on the flow of water, on the character of the terrestrial surface, and on the distribution of life. Human interference affects meteorological conditions—by removing forests and laying bare to the sun and winds areas which were previously kept cool and damp under the trees, or which, lying on the lee side, were protected from tempests; as already stated, it is supposed that the wholesale destruction of the forests formerly existing in countries bordering the Mediterranean has been in part the cause of the desiccation of these districts by drainage, the effect of this operation being to remove rapidly the diseharg-cd rainfall, to lessen evaporation, and thereby to diminish the rain fall and somewhat increase the general temperature of a country; by the other processes of agriculture, suet' as the transformation of moor and bog into cultivated land, and the clothing of bare hillsides with green crops or plantations of coniferous. and 11M.dwood trees. By increasing or diminishing the rainfall man directly affects the course of the waters over the land. By his drainage operations, be makes the rain to run off more rapidly than before, and thereby increases the floods in the rivers. By wells, bores, mines, or other stibterraneous works he interferes with the underground waters and con sequently with the discharge of springs. By embanking rivers he confines them to narrow/channels, sometimes increasing their scour, and enabling them to carry their sediment further seaward; sometimes causing them to deposit it over the plains and raise their level. Man's operations alter the aspect of a country in many ways; by making forest-clad mountains bare, or clothing bare mountains with forest; by promoting the growth or causing the removal of peat-mosses; by heedlessly uncovering sand,dunes, and thereby setting in motion a process of destruction which may convert hundreds of acres of fertile land into waste sand, or by prudently planting the dunes with sand loving vegetation or pines, and thus arresting their landward progress: by so guiding the course of rivers as to make them aid him in reclaiming waste land and bringing it under cultivation: by piers and bulwarks, whereby the ravages of the sea are stayed; or by the thoughtless removal from the beach of stones which the waves had themselves thrown up, and which would have served for a time to protect the land; by forming new deposits either designedly or incidentally. The, roads, bridges, canals, railways,
tunnels, villages, and towns with which man has covered the surface of the land will in many cases. form a permanent record of his presence. Under his hand the whole surface of civilized countries is very slowly covered with a stratum, either formed wholly by him, or due in great measure to his operations, and containing many relics of his presence. The earth of'old cities has been raised many feet by the rubbish of his buildings; the level of the streets of modern Rome stands high above that of the pave ments of the Caesars, and that again above the roadways of the early republic. Over cultivated fields his potsherds are turned up in abundance by the plow. The loam has risen within the walls of his graveyards, as generation after generation has moldered there into dust. It is on the Distribution of Life, perhaps, that the most subtle of human influences come. Sonic of man's doings in this domain are indeed plain enough, such as the extirpation of wild animals, the diminution or destruction of some forms of vegetation, the introduction of plants and animals useful to himself, and especially the enormous predominance given by him to the cereals and to the spread of sheep and cattle. But no such extensive disturbance of the normal conditions of the distribution of life can take place without carrying with it many secondary effects, and setting in motion a wide cycle of change and of reaction in the animal and vegetable kingdoms. For example, the incessant warfare waged by man against birds and beasts of prey in districts given up to the chase leads sometimes to unforeseen results. The weak game is allowed to live which would otherwise be killed off and give room for the more healthy remainder. Other animals whieh feed perhaps on the same materials as the game are by the same cause permitted to live unchecked, and thereby to act as a further hindrance to the spread of the protected species. But the indirect results of man's inter ference with the regime of plants and animals still require much prolonged observation.