nt that we
understand the many complex contingencies, on which the existence of
each species depends. If we forget for an instant, that each species
tends to increase inordinately, and that some check is always in action,
yet seldom perceived by us, the whole economy of nature will be utterly
obscured. Whenever we can precisely say why this species is more
abundant in individuals than that; why this species and not another
can be naturalised in a given country; then, and not till then, we may
justly feel surprise why we cannot account for the extinction of this
particular species or group of species.

ON THE FORMS OF LIFE CHANGING ALMOST SIMULTANEOUSLY THROUGHOUT THE
WORLD.

Scarcely any palaeontological discovery is more striking than the fact,
that the forms of life change almost simultaneously throughout the
world. Thus our European Chalk formation can be recognised in many
distant parts of the world, under the most different climates, where not
a fragment of the mineral chalk itself can be found; namely, in North
America, in equatorial South America, in Tierra del Fuego, at the
Cape of Good Hope, and in the peninsula of India. For at these distant
points, the organic remains in certain beds present an unmistakeable
degree of resemblance to those of the Chalk. It is not that the same
species are met with; for in some cases not one species is identically
the same, but they belong to the same families, genera, and sections
of genera, and sometimes are similarly characterised in such trifling
points as mere superficial sculpture. Moreover other forms, which are
not found in the Chalk of Europe, but which occur in the formations
either above or below, are similarly absent at these distant points of
the world. In the several successive palaeozoic formations of Russia,
Western Europe and North America, a similar parallelism in the forms of
life has been observed by several authors: so it is, according to Lyell,
with the several European and North American tertiary deposits. Even
if the few fossil species which are common to the Old and New Worlds be
kept wholly out of view, the general parallelism in the successive forms
of life, in the stages of the widely separated palaeozoic and tertiary
periods, would still be manifest, and the several formations could be
easily correlated.

These observations, however, relate to the marine inhabitants of distant
parts of the world: we have not sufficient data to judge whether the