ant, or _megatherium_, but was intimately related to
the Gnawers, the order which at the present day includes most of the
smallest quadrupeds; and judging from the position of the eyes, ears,
and nostrils, it was probably aquatic.

We have good evidence that these gigantic quadrupeds, more different
from those of the present day than the oldest of the Tertiary quadrupeds
of Europe, lived whilst the sea was peopled with most of its present
inhabitants. These animals migrated on land, since submerged, near
Behring's Strait, from Siberia into North America, and thence on land,
since submerged, in the West Indies into South America, where they
mingled with the forms characteristic of that southern continent, and
have since become extinct.

The existing animals of the pampas include the puma, the South American
lion, while the birds are numerous. The largest is the ostrich, which is
found in groups. The ostriches are fleet in pace, prefer running against
the wind, and freely take to the water. At first start they expand their
wings, and, like a vessel, make all sail. Of mammalia, the jaguar, or
South American tiger, is the most formidable. It frequents the wooded
and reedy banks of the great rivers. There are four species of
armadilloes, notable for their smooth, hard, defensive covering. Of
reptiles there are many kinds. One snake, a _trigonocephalus_, has in
some respects the structure of a viper with the habits of a rattlesnake.
The expression of this snake's face is hideous and fierce. I do not
think I ever saw anything more ugly, excepting, perhaps, some of the
viper-bats.

_III.--In the Extreme South_

From the Rio Plata the course of the Beagle was directed to the mouth of
the Santa Cruz river, on the coast of Patagonia. One evening, when we
were about ten miles from the bay of San Blas, vast numbers of
butterflies, in bands and flocks of countless myriads, extended as far
as the eye could range. One dark night, with a fresh breeze, the foam
and every part of the surface of the waves glowed with a pale light. The
vessel drove before her bows two billows of liquid phosphorus, and in
her wake she was followed by a milky train. I am inclined to consider
that the phosphorescence is the result of organic particles, by which
process (one is tempted almost to call it a kind of respiration) the
ocean becomes purified.

The geology of Patagonia is interesting. For hundreds of miles of coast
there is one great deposit c