the coast about twenty-five feet. Nor if the ground sinks fifty
feet at a time, as in the harbor of Port Royal, in Jamaica, in 1692,
will such alterations of level work any general fluctuations in the
state of organic beings inhabiting the West Indian Islands, or the
Caribbean Sea.

It is only when the subterranean powers, by shifting gradually the
points where their principal force is developed, happen to strike upon
some particular region where a slight change of level immediately
affects the distribution of land and water, or the state of the climate,
or the barriers between distinct groups of species over extensive areas,
that the rate of fluctuation becomes accelerated, and may, in the course
of a few years or centuries, work mightier changes than had been
experienced in myriads of antecedent years.

Thus, for example, a repetition of subsidences causing the narrow
isthmus of Panama to sink down a few hundred feet, would, in a few
centuries, bring about a great revolution in the state of the animate
creation in the western hemisphere. Thousands of aquatic species would
pass, for the first time, from the Caribbean Sea into the Pacific; and
thousands of others, before peculiar to the Pacific Ocean, would make
their way into the Caribbean Sea, the Gulf of Mexico, and the Atlantic.
A considerable modification would probably be occasioned by the same
event in the direction or volume of the Gulf stream, and thereby the
temperature of the sea and the contiguous lands might be altered as far
as the influence of that current extends. A change of climate might thus
be produced in the ocean from Florida to Spitzbergen, and in many
countries of North America, Europe, and Greenland. Not merely the heat,
but the quantity of rain which falls, would be altered in certain
districts, so that many species would be excluded from tracts where they
before flourished: others would be reduced in number; and some would
thrive more and multiply. The seeds also and the fruits of plants would
no longer be drifted in precisely the same directions, nor the eggs of
aquatic animals; neither would species be any longer impeded in their
migrations towards particular stations before shut out from them by
their inability to cross the mighty current.

Let us take another example from a part of the globe which is at present
liable to suffer by earthquakes, namely, the low sandy tract which
intervenes between the sea of Azof and the Caspian. If there