In succeeding years they were introduced into other places where the
Spaniards settled; and, in the space of half a century, they were found
established in the New World, from the latitude of 25 deg. north, to the
40th deg. of south latitude. Sheep, also, and goats have multiplied
enormously in the New World, as have also the cat and the rat, which last,
as we before stated, has been imported unintentionally in ships. The dogs
introduced by man, which have at different periods become wild in America,
hunted in packs like the wolf and the jackal, destroying not only hogs,
but the calves and foals of the wild cattle and horses.

Ulloa in his voyage, and Buffon on the authority of old writers, relate a
fact which illustrates very clearly the principle before explained by us,
of the check which the increase of one animal necessarily offers to that
of another. The Spaniards had introduced goats into the island of Juan
Fernandez, where they became so prolific as to furnish the pirates who
infested those seas with provisions. In order to cut off this resource
from the bucaneers, a number of dogs were turned loose into the island;
and so numerous did they become in their turn, that they destroyed the
goats in every accessible part, after which the number of the wild dogs
again decreased.

As an example of the rapidity with which a large tract may become peopled
by the offspring of a single pair of quadrupeds, we may mention that in
the year 1773, thirteen rein-deer were exported from Norway, only three of
which reached Iceland. These were turned loose into the mountains of
Guldbringe Syssel, where they multiplied so greatly, in the course of
forty years, that it was not uncommon to meet with herds consisting of
from forty to one hundred in various districts.--_Lyell's Geology_, vol.
ii.