btless 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 (_epaisseur_) 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
debris 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 debris, 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 debris of organisms is
manifestly inadequate, our aerial 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