species thus produced being themselves dominant owing to inheritance,
and to having already had some advantage over their parents or over
other species; these again spreading, varying, and producing new
species. The forms which are beaten and which yield their places to the
new and victorious forms, will generally be allied in groups, from
inheriting some inferiority in common; and therefore as new and
improved groups spread throughout the world, old groups will disappear
from the world; and the succession of forms in both ways will
everywhere tend to correspond.
There is one other remark connected with this subject worth making. I
have given my reasons for believing that all our greater fossiliferous
formations were deposited during periods of subsidence; and that blank
intervals of vast duration occurred during the periods when the bed of
the sea was either stationary or rising, and likewise when sediment was
not thrown down quickly enough to embed and preserve organic remains.
During these long and blank intervals I suppose that the inhabitants of
each region underwent a considerable amount of modification and
extinction, and that there was much migration from
other parts of the world. As we have reason to believe that large areas
are affected by the same movement, it is probable that strictly
contemporaneous formations have often been accumulated over very wide
spaces in the same quarter of the world; but we are far from having any
right to conclude that this has invariably been the case, and that
large areas have invariably been affected by the same movements. When
two formations have been deposited in two regions during nearly, but
not exactly the same period, we should find in both, from the causes
explained in the foregoing paragraphs, the same general succession in
the forms of life; but the species would not exactly correspond; for
there will have been a little more time in the one region than in the
other for modification, extinction, and immigration.
I suspect that cases of this nature have occurred in Europe. Mr.
Prestwich, in his admirable Memoirs on the eocene deposits of England
and France, is able to draw a close general parallelism between the
successive stages in the two countries; but when he compares certain
stages in England with those in France, although he finds in both a
curious accordance in the numbers of the species belonging to the same
genera, yet the species themselves differ in a manner very difficult to
account for, considering the proximity of the two areas, unless,
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