lly choking it up with ashes and lava, might produce a new barrier
as effectually as a series of earthquakes; especially if thermal
springs, charged with carbonate of lime, silica, and other mineral
ingredients, should promote the rapid multiplication of corals and
shells, and cement them together with solid matter precipitated during
the intervals between eruptions. Suppose in this manner a stoppage to be
caused of the Bahama channel between the bank of that name and the coast
of Florida. This insignificant revolution, confined to a mere spot in
the bottom of the ocean, would, by diverting the main current of the
Gulf stream, give rise to extensive changes in the climate and
distribution of animals and plants inhabiting the northern hemisphere.

_Illustration from the formation of new islands._--A repetition of
elevatory movements of earthquakes might continue over an area as
extensive as Europe, for thousands of ages, at the bottom of the ocean,
in certain regions, and produce no visible effects; whereas, if they
should operate in some shallow parts of the Pacific, amid the coral
archipelagos, they would soon give birth to a new continent. Hundreds of
volcanic islands may be thrown up, and become covered with vegetation,
without causing more than local fluctuations in the animate world; but
if a chain like the Aleutian archipelago, or the Kurile Isles, run for a
distance of many hundred miles, so as to form an almost uninterrupted
communication between two continents, or two distant islands, the
migrations of plants, birds, insects, and even of some quadrupeds, may
cause, in a short time, an extraordinary series of revolutions tending
to augment the range of some animals and plants, and to limit that of
others. A new archipelago might be formed in the Mediterranean, the Bay
of Biscay, and a thousand other places, and might produce less important
events than one rock which should rise up between Australia and Java, so
placed that winds and currents might cause an interchange of the plants,
insects, and birds.

_From the wearing through of an isthmus._--If we turn from the igneous
to the aqueous agents, we find the same tendency to an irregular rate of
change, naturally connected with the strictest uniformity in the energy
of those causes. When the sea, for example, gradually encroaches upon
both sides of a narrow isthmus, as that of Sleswick, separating the
North Sea from the Baltic, where, as before stated, the cliffs