the lower plains, which latter are identical in proportional numbers with
those now cast up on the beach. From this circumstance, and from not
finding, upon careful examination, near Coquimbo any shells at a greater
height than 252 feet, I believe that the recent elevation there has been
much less than at Valparaiso, where it has been 1,300 feet, and I may add,
than at Concepcion. This considerable inequality in the amount of elevation
at Coquimbo and Valparaiso, places only 200 miles apart, is not improbable,
considering, first, the difference in the force and number of the shocks
now yearly affecting different parts of this coast; and, secondly, the fact
of single areas, such as that of the province of Concepcion, having been
uplifted very unequally during the same earthquake. It would, in most
cases, be very hazardous to infer an inequality of elevation, from shells
being found on the surface or in superficial beds at different heights; for
we do not know on what their rate of decay depends; and at Coquimbo one
instance out of many has been given, of a promontory, which, from the
occurrence of one very small collection of lime-cemented shells, has
indisputably been elevated 242 feet, and yet on which, not even a fragment
of shell could be found on careful examination between this height and the
beach, although many sites appeared very favourable for the preservation of
organic remains: the absence, also, of shells on the gravel-terraces a
short distance up the valley of Coquimbo, though abundant on the
corresponding terraces at its mouth, should be borne in mind.

There are other epochs, besides that of the existence of recent Mollusca,
by which to judge of the changes of level on this coast. At Lima, as we
have just seen, the elevation has been at least eighty-five feet, within
the Indo-human period; and since the arrival of the Spaniards in 1530,
there has apparently been a sinking of the surface. At Valparaiso, in the
course of 220 years, the rise must have been less than nineteen feet; but
it has been as much as from ten to eleven feet in the seventeen years