mple organisms, able to
flourish under simple conditions of life, would be the first successful
immigrants; and that more complex organisms, needing for their existence
the fulfilment of more complex conditions, would afterwards establish
themselves in something like an ascending succession. At the one extreme
we see every facility. The new individuals can be conveyed in the shape
of minute germs; immense numbers of these are perpetually being carried
in all directions to great distances by ocean-currents--either detached
or attached to floating bodies; they can find nutriment wherever they
arrive; and the resulting organisms can multiply asexually with great
rapidity. At the other extreme, we see every difficulty. The new
individuals must be conveyed in their adult forms; their numbers are, in
comparison, utterly insignificant; they live on land, and are very
unlikely to be carried out to sea; when so carried, the chances are
immense against their escape from drowning, starvation, or death by
cold; if they survive the transit, they must have a pre-existing Flora
or Fauna to supply their special food; they require, also, the
fulfilment of various other physical conditions; and unless at least two
individuals of different sexes are safely landed, the race cannot be
established. Manifestly, then, the immigration of each successively
higher order of organisms, having, from one or other additional
condition to be fulfilled, an enormously-increased probability against
it, would naturally be separated from the immigration of a lower order
by some period like a geologic epoch. And thus the successive
sedimentary deposits formed while this new continent was undergoing
gradual elevation, would seem to furnish clear evidence of a general
progress in the forms of life. That lands thus raised up in the midst of
a wide ocean, would first give origin to unfossiliferous strata; next,
to strata containing only the lowest marine forms; next to strata
containing only the higher marine forms, ascending finally to fish; and
that the strata above these would contain reptiles, then small mammals,
then great mammals; seems to us demonstrable. And if the succession of
fossils presented by the strata of this supposed new continent, would
thus simulate the succession presented by our own sedimentary series;
must we not conclude that our own sedimentary series very possibly
records nothing more than the phenomena accompanying one of these great
up