on successive beach-lines during a gradual elevation of the land. The
presence, however, of so many whole and perfectly preserved shells appears
at first a difficulty on this view, considering that the coast is exposed
to the full force of an open ocean: but we may suppose, either that these
shells were thrown during gales on flat ledges of rock just above the level
of high-water mark, and that during the elevation of the land they are
never again touched by the waves, or, that during earthquakes, such as
those of 1822, 1835, and 1837, rocky reefs covered with marine-animals were
it one blow uplifted above the future reach of the sea. This latter
explanation is, perhaps, the most probable one with respect to the beds at
Concepcion entirely composed of the Mytilus Chiloensis, a species which
lives below the lowest tides; and likewise with respect to the great beds
occurring both north and south of Valparaiso, of the Mesodesma
donaciforme,--a shell which, as I am informed by Mr. Cuming, inhabits
sandbanks at the level of the lowest tides. But even in the case of shells
having the habits of this Mytilus and Mesodesma, beds of them, wherever the
sea gently throws up sand or mud, and thus protects its own accumulations,
might be upraised by the slowest movement, and yet remain undisturbed by
the waves of each new beach-line.

It is worthy of remark, that nowhere near Valparaiso above the height of
twenty feet, or rarely of fifty feet, I saw any lines of erosion on the
solid rocks, or any beds of pebbles; this, I believe, may be accounted for
by the disintegrating tendency of most of the rocks in this neighbourhood.
Nor is the land here modelled into terraces: Mr. Alison, however, informs
me, that on both sides of one narrow ravine, at the height of 300 feet
above the sea, he found a succession of rather indistinct step-formed
beaches, composed of broken shells, which together covered a space of about
eighty feet vertical.