"The other cause, as we shall see, is found in the detritus of organic bodies successively accumulated, which perpetually elevates, although with extreme slowness, the soil of the dry portions of the globe, and which does it all the more rapidly, as the situation of these parts gives less play to the degradation of the surface caused by the rivers. "Doubtless a plain which is destined some day to furnish the mountains which the rivers will carve out from its mass would have, when still but a little way from the sea, but a moderate elevation above its river channels; but gradually as the ocean basin removed from this plain, this basin constantly sinking down into the interior (_épaisseur_) of the external crust of the globe, and the soil of the plain perpetually rising higher from the deposition of the detritus of organic bodies, it results that, after ages of elevation of the plain in question, it would be in the end sufficiently thick for high mountains to be shaped and carved out of its mass. "Although the ephemeral length of life of man prevents his appreciation of this fact, it is certain that the soil of a plain unceasingly acquires a real increase in its elevation in proportion as it is covered with different plants and animals. Indeed the débris successively heaped up for numerous generations of all these beings which have by turns perished, and which, as the result of the action of their organs, have, during the course of this life, given rise to combinations which would never have existed without this means, most of the principles which have formed them not being borrowed from the soil; this débris, I say, wasting successively on the soil of the plain in question, gradually increases the thickness of its external bed, multiplies there the mineral matters of all kinds and gradually elevates the formation." Our author, as is evident, had no conception, nor had any one else at the time he wrote, of the slow secular elevation of a continental plateau by crust-movements, and Lamarck's idea of the formation of elevated plains on land by the accumulation of débris of organisms is manifestly inadequate, our aërial or eolian rocks and loess being wind-deposits of sand and silt rather than matters of organic origin. Thus he cites as an example of his theory the vast elevated plains of Tartary, which he thought had been dry land from time immemorable, though we now know that the rise took place in the quaternary or present period. On the other hand, given these vast elevated plains, he was correct in affirming that rivers flowing through them wore out enormous valleys and carved out high mountains, left standing by atmospheric erosion, for examples of such are to be seen in the valley of the Nile, the Colorado, the Upper Missouri, etc. He then distinguishes between granitic or crystalline mountains, and those composed of stratified rocks and volcanic mountains.