Page:Popular Science Monthly Volume 32.djvu/631

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bottom of stone or contiguous rock." Palissy further sought means for establishing artificial fountains "in imitation of nature and as nearly approaching it as possible, by following the method of the sovereign Fountain-maker." He added the profound thought, which lies to-day at the foundation of experimental geology, "It is impossible to imitate Nature in anything, except we first contemplate her effects, and take her for our pattern and example." Hence we understand why springs are inexhaustible, because they are unceasingly renewed by the play of permanent forces; they result from a circulation which is in some respects symmetrical with the great aerial circulation of water.

Violent phenomena, like earthquakes, have certainly the prerogative of exciting the imagination. But other phenomena, though they take place slowly and in silence, are none the less worthy of interest; of this character are the mechanism and the fruitful action of the subterranean waters, of which springs are the exterior manifestation. Aside from their usefulness to man, the importance of the study of them is all the greater in that their work is not alone applicable to the present time. Since the crust of the earth has existed, and during all the periods of its development, the water circulating within it, sometimes at very high temperatures, has produced considerable and varied effects, which have in one way or another durably registered themselves, and the explanation of which is facilitated by recent experiments. It is, in fact, this incessant circulation which has engendered a large number of mineral species. The present functions of underground waters will first engage our attention, the examination of their part in the formation of minerals in ancient epochs being reserved for future studies.

As the course of rivers depends on the exterior contours of the soil, so is the régime of subterranean waters an immediate consequence of the nature and mode of arrangement of the masses through which they move.

Except for a very thin covering of vegetable soil, which is a kind of epidermis, the crust of the earth is composed of materials to which the name of rocks is applied, even when, like sand and clay, they are of little coherency. All of these masses have been formed successively, during periods of extremely long duration, and in the midst of conditions of which they bear in themselves the characteristic marks. They are veritable monuments, which delineate in their essential traits the successive revolutions of our globe.

The rocks constituting the greater part of the continents are called stratified, because they are divided into large parallel layers, to which are given the name of strata or beds. It is certain that the rocks of this category, whatever their composition, have been formed in the seas or lakes by sediments and organisms: a sure proof of this truth is furnished by their pebbles and sands, the origin of which can