truths of paleontology testify in relation to the common doctrines of
progressive modification, which suppose that modification to have taken
place by a necessary progress from more to less embryonic forms, or
from more to less generalized types, within the limits of the period
represented by the fossiliferous rocks?

It negatives those doctrines; for it either shows us no evidence of any
such modification, or demonstrates it to have been very slight; and as
to the nature of that modification, it yields no evidence whatsoever
that the earlier members of any long-continued group were more
generalized in structure than the later ones. To a certain extent,
indeed, it may be said that imperfect ossification of the vertebral
column is an embryonic character; but, on the other hand, it would be
extremely incorrect to suppose that the vertebral columns of the older
Vertebrata are in any sense embryonic in their whole structure.

Obviously, if the earliest fossiliferous rocks now known are coeval with
the commencement of life, and if their contents give us any just
conception of the nature and the extent of the earliest fauna and
flora, the insignificant amount of modification which can be
demonstrated to have taken place in any one group of animals, or
plants, is quite incompatible with the hypothesis that all living forms
are the results of a necessary process of progressive development,
entirely comprised within the time represented by the fossiliferous
rocks.

Contrariwise, any admissible hypothesis of progressive modification must
be compatible with persistence without progression, through indefinite
periods. And should such an hypothesis eventually be proved to be
true, in the only way in which it can be demonstrated, viz. by