be out of place if we attempt to summarise,
in the briefest possible manner, some of the principal results
which may be deduced as to the succession of life upon the earth
from the facts which have in the preceding portion of this work
been passed in review. That there was a time when the earth was
void of life is universally admitted, though it may be that the
geological record gives us no direct evidence of this. That the
globe of to-day is peopled with innumerable forms of life whose
term of existence has been, for the most part, but as it were
of yesterday, is likewise an assertion beyond dispute. Can we
in any way connect the present with the remote past, and can we
indicate even imperfectly the conditions and laws under which the
existing order was brought about? The long series of fossiliferous
deposits, with their almost countless organic remains, is the
link between what has been and what is; and if any answer to the
above question can be arrived at, it will be by the careful and
conscientious study of the facts of Palaeontology. In the present
state of our knowledge, it may be safely said that anything like
a dogmatic or positive opinion as to the precise sequence of
living forms upon the globe, and still more as to the manner in
which this sequence may have been brought about, is incapable of
scientific proof. There are, however, certain general deductions
from the known facts which may be regarded as certainly established.

In the first place, it is certain that there has been a _succession_
of life upon the earth, different specific and generic types
succeeding one another in successive periods. It follows from
this, that the animals and plants with which we are familiar
as living, were not always upon the earth, but that they have
been preceded by numerous races more or less differing from them.
What is true of the species of animals and plants, is true also
of the higher zoological divisions; and it is, in the second
place, quite certain that there has been a similar _succession_
in the order of appearance of the primary groups ("sub-kingdoms,"
"classes," &c.) of animals and vegetables. These great groups
did not all come into existence at once, but they made their
appearance successively. It is true that we cannot be said to
be certainly acquainted with the first _absolute_ appearance of
any great group of animals. No one dare assert positively that
the apparent first appearance of Fishes in the Upper