between our consecutive formations; and in these intervals there may
have been much slow extermination. Moreover, when by sudden immigration
or by unusually rapid development, many species of a new group have
taken possession of a new area, they will have exterminated in a
correspondingly rapid manner many of the old inhabitants; and the forms
which thus yield their places will commonly be allied, for they will
partake of some inferiority in common.
Thus, as it seems to me, the manner in which single species and whole
groups of species become extinct, accords well with the theory of
natural selection. We need not marvel at extinction; if we must marvel,
let it be at our presumption in imagining for a moment 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 pal ontological 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 pal ozoic formations of Russia,
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