« AnteriorContinuar »
of solid granite, as hard and impermeable as most of the rocks of that kind are which rise to the surface of the earth? If such granite continents could not have been disintegrated, and no permanent rivers could have run from them to boar off their detritus, is it not clear that they never could have furnished the materials of which the strata were formed? Have geologists noticed these difficulties in framing their theory? Have they proceeded in their calculations on the assumption that their fancied continents, instead of consisting exclusively of granite, were covered with loose soil, like the present lands of the globe, and were traversed by numerous permanent streams and rivers? Is that legitimate? Does the fact that some measure of mud, sand, and vegetable matter is borne to the sea by the continually running rivers of the present globe, which is covered by a deep layer of loose earth, and annually shoots up a vast growth of vegetables, prove that an equal quantity of similar matter would annually be borne to the sea from mere granite continents, which had neither any loose earth nor vegetable matter on their surface--nor any rivers to bear such materials, if they existed, to the ocean? Recapitulate the several impracticable positions they have thus incorporated in their theory of the origin of the strata.
The false Theories of Geologists respecting the Sources of the Materials of which
the Strata were formed.
But let us suppose that the chemical and mechanical agents that may be presumed to have acted on those rocky continents would have rapidly disintegrated their surface, and reduced them on a vast scale to such minute particles as could have been transported by streams to the sea; and their theory still continues embarrassed with equally insurmountable difficulties. For they proceed in it on the assumption, first, that their whole mass would, during the progress of the process, be converted into detritus; and next, that every particle of the detritus produced from them would be borne to the sea, and enter into the composition of the strata ; as otherwise they must have been of a still more enormous height than that which is assigned to them. As the bulk, which we have indicated as ascribed to them by the theory, is only equal to that of the strata which are held to have been formed from them, if but one third, one half, or three quarters of their mass is supposed to have been transferred to the sea, then they must have been of a still greater bulk, in order that that proportion may correspond to the dimensions of the strata that are held to have been built out of their ruins. But neither of those conditions is consistent with the laws that govern the disintegration of mountains and the transportation of their detritus to the ocean. Let us, in the first place, suppose the surface of those imagined continents to have become disintegrated to such a depth that the fragments and levigated particles, if spread out on the bottom of the ocean, would have formed a stratum of several feet in thickness; and yet no known or conceivable agency of streams, torrents, and rivers could have ever conveyed the whole, or any considerable portion of them, to the sea. The supposition is as inadmissible and preposterous as the fancy were that the rivulets and streams now running, can ever bear to the ocean all the comminuted dust, sand, and gravel with which our present continents and islands are overspread. So far from achieving such a stupendous result, they would never have made any more appreciable progress towards it than our present rivers have made in reducing the elevation of the continents and diminishing the quantity of dry land. If they were shaped, like the continents of this hemisphere, with a vast range of mountains running through their whole length along their western verge, so that no rains could have fallen on
their western slope to bear their debris on that side to the ocean; and if from the foot of that range on the east they were spread out like the vast regions of South America, that are traversed by the La Plata, the Amazon, and the Orinoco, and the immense plains and prairies drained in this division of the continent by the Mississippi, the St. Lawrence, and the Mackenzie, it is obvious that their detritus could never in any great quantity have been transported to the ocean. Ninety-nine parts out of a hundred--probably nine hundred and ninety-nine out of a thousandwould for ever have remained where they fell, as the materials that constitute the surface of our present continents have continued where they were first formed. The rivulets and rivers that are of sufficient force to bear particles of earth and sand from their places towards the sea, probably do not come in contact even with one particle in millions of those that constitute the soils and debris that are spread on the surface. They act only on the narrow line of their channels, which, compared to the whole area, are but. what the lines of longitude marked on an artificial globe are to the spaces that lie between them. If the supposed continents were formed like Europe, with a few lofty ranges, from the bases of which vast plains extended like those of the Po, the Rhine, and the Danube, or immense levels like those that stretch from the Baltic to the Ural Mountains, and the
steppes of northern Asia, then also a great share of their detritus must for ever have remained where it originated; and that would have been still more emphatically the fact, if, like Australia, their interior through vast spaces was depressed below the level of their coasts, so that the waters falling on them could have no outlet to the ocean. Whatever might have been their forms, therefore, if they corresponded in any considerable measure to those of our present continents, the transportation of any large quantity of detritus from their general surface by torrents and rivers must have been wholly impossible. We havo in the vast experiment that has been made on our present continents for four thousand years, the most ample demonstration that streams and rivers are altogether inadequate to such an effect. Were all the detrital matter that has in that period been borne by them from the dry land, and now lies buried beneath the seas, restored to the places from which it was removed, the largest portion of it would undoubtedly be lodged along the line of the streams. The share that nine tenths of the surface would receive would scarcely be appreciable.
And next, the conversion of the whole mass of those granite continents into detritus—the other condition of their theory-would be equally impossible. For the rate of disintegration and the area on which it took place, instead of advancing or continuing the