Principles of Geology Volume 3 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1840 Excerpt: ...of the globe; for we must class his agency among the powers of organic nature. Felling of forests.--The felling of forests has been attended, in many countries, by a diminution of rain, as in Barbadoes and Jamaica. For in tropical countries, where the quantity of aqueous vapour in the atmosphere is great, but where, on the other hand, the - De la Beche, Geol. Man., p. 184 first ed. t Phil. Trans., vol.ii. p. 294. direct rays of the sun are most powerful, any impediment to the free circulation of air, or any screen which shades the earth from the solar rays, becomes a source of humidity; and wherever dampness and cold have begun to be generated by such causes, the condensation of vapour continues. The leaves, moreover, of all plants are alembics, and some of those in the torrid zone have the remarkable property of distilling water, thus contributing to prevent the earth from becoming parched up. Distribution of the American forests.--There can be no doubt, then, that the state of the climate, especially the humidity of the atmosphere, influences vegetation, and that, in its turn, vegetation re-acts upon the climate; but some writers seem to have attributed too much importance to the influence of forests, particularly those of America, as if they were the primary cause of the moisture of the climate. The theory of a modern author on this subject that forests exist in those parts of America only where the predominant winds carry with them a considerable quantity of moisture from the ocean, seems far more rational. In all countries, he says, having a summer heat exceeding 70, the presence or absence of natural woods, and their greater or less luxuriance, may be taken as a measure of the amount of humidity, and of the fertility of the so...