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Show ~06 INFLUENCE OF MAN IN MODIFYING [Ch. XII. analogous in the agency of inferior beings. . For we ought always, before we decide that any part of the mfl.uence of man is novel and anomalous, carefully to consider all the powers of oth er am.m a t e agen t s wh i'ch may be limited or superseded by him. Many who have reasoned on these subjects seem to have forgotten that the human race often succeeds to th.e dis. charge of functions previously fulfilled by other species ; a topic on which we have already offered some hints, wh~n explaining how the distribution and numbers. of each species are dependent on the state of contemporary bemgs. Suppose the growth of some of the larger terrestrial plants, or in other words, the extent of forests, to be diminished by m~n and the climate to be thereby modified, it does not follow that' this kind of innovation is unprecedented. It is a change in the state of the vegetation, and such may often have been the result of the entrance of new species into the earth. The multiplication, for example, of certain insects in parts of Germany during the last century, destroyed more trees than man, perha~s, could have felled during an equal period. It is a curious fact, to which we shall again advert, that the sites of many European forests~ cut down since the time of the Romans, have become peat-mosses; and thus a permanent change has been effected in these regions. But other woods, blown down by winds, in the same countries, have also become peat-bogs; so that, although man may have accelerated s.omewhat the change, yet it may be doubted whether other ammate and inanimate causes might not, without his interference, have produced similar results. The atmosphere of our ~atitudes may have been slowly and insensibly cooling down smce. the ancient forests began to grow, and the time may have arrived when slight accidents were sufficient to cause the decrease of trees, and the usurpation of their site by other plants. We do not pretend to decide how far the power of man, to modify the surface, may differ in kind or degree from. that of other living beings, but we suspect that the problem IS more complex than has. been imagined by many who have speculated Ch. XII.] THE PHYSICAL GEOGRAPHY OF THE GLOBE. ~07 on such topics. If new land be raised from the sea the great-est alteration in its ph ys I. ca 1 con dI' ti·O n, wh 1' c h could' ever ari·s e from the influence of organic beings, would probably be produced by the first immigration of terrestrial plants, whereby the ~ra~t would become covered with vegetation. 'l'he change next m Importan~e would seem to be when animals enter, and modify the proportiOnate numbers of certain species of plants. If there be any anomaly in the intervention of man in farther varying the relati.ve ~umber~ in the vegetable kingdom, it may ~ot so ~uch con.sist m the kmd or absolute quantity of alteration, as m the Circumstance that a single species, in this case would exert, by its superior power and universal distribution' an m. fl uence equal to that of hundreds of other terrestria'l animals. If we inquire whether man, by his direct removing power, or by the changes which he may give rise to indirectly, tends, upon the whole, to lessen or increase the inequalities of the ear~h's surface, we shall incline, perhaps, to the opinion that he IS a levelling agent. He conveys upwards a certain quantity o~ materials from the bowels of the earth in mining operatiOns; but, on the other hand, much rock is taken annually from the land, in the shape of ballast, and afterwards thrown into the sea, whereby, in spite of prohibitory laws many harbours, in various parts of the world, have been blocked up. We rarely transport heavy materials to higher levels, and our pyramids and cities are chiefly constructed of stone brought down from more elevated situations. By ploughing up thousands of square miles, and exposing a surface for part of the year to the action of the elements, we assist the abrading force of rain, and destroy the conservative effects of vegetation. But the ag~regate force exerted by man is truly insignificant, when we consider the operations of the great physical causes, whether aqueous or igneous, in the inanimate world. If all the nat~ons of the earth should attempt to quarry a way the lava which flowed during one eruption from the Icelandic volcanoes |