Considering the
enormous power of denudation which the sea possesses, as shown by
numberless facts, it is not probable that a sedimentary deposit,
when being upraised, could pass through the ordeal of the beach, so
as to be preserved in sufficient masses to last to a distant
period, without it were originally of wide extent and of
considerable thickness: now it is impossible on a moderately
shallow bottom, which alone is favourable to most living creatures,
that a thick and widely extended covering of sediment could be
spread out, without the bottom sank down to receive the successive
layers. This seems to have actually taken place at about the same
period in southern Patagonia and Chile, though these places are a
thousand miles apart. Hence, if prolonged movements of
approximately contemporaneous subsidence are generally widely
extensive, as I am strongly inclined to believe from my examination
of the Coral Reefs of the great oceans--or if, confining our view
to South America, the subsiding movements have been coextensive
with those of elevation, by which, within the same period of
existing shells, the shores of Peru, Chile, Tierra del Fuego,
Patagonia, and La Plata have been upraised--then we can see that at
the same time, at far distant points, circumstances would have been
favourable to the formation of fossiliferous deposits, of wide
extent and of considerable thickness; and such deposits,
consequently, would have a good chance of resisting the wear and
tear of successive beach-lines, and of lasting to a future epoch.
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