Lyell has made similar
observations on some of the later tertiary formations. Barrande, also,
shows that there is a striking general parallelism in the successive
Silurian deposits of Bohemia and Scandinavia; nevertheless he finds a
surprising amount of difference in the species. If the several formations
in these regions have not been deposited during the same exact periods--a
formation in one region often corresponding with a blank interval in the
other--and if in both regions the species have gone on slowly changing
during the accumulation of the several formations and during the long
intervals of time between them; in this case the several formations in the
two regions could be arranged in the same order, in accordance with the
general succession of the forms of life, and the order would falsely appear
to be strictly parallel; nevertheless the species would not all be the same
in the apparently corresponding stages in the two regions.
ON THE AFFINITIES OF EXTINCT SPECIES TO EACH OTHER, AND TO LIVING FORMS.
Let us now look to the mutual affinities of extinct and living species.
All fall into a few grand classes; and this fact is at once explained on
the principle of descent. The more ancient any form is, the more, as a
general rule, it differs from living forms. But, as Buckland long ago
remarked, extinct species can all be classed either in still existing
groups, or between them.
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