relation to the time occupied by the deposition of geological formations,
is extraordinarily small. Of all animals the higher _Vertebrata_ are the
most complex; and among these the carnivores and hoofed animals
(_Ungulata_) are highly differentiated. Nevertheless, although the
different lines of modification of the _Carnivora_ and those of the
_Ungulata_, respectively, approach one another, and, although each group
is represented by less differentiated forms in the older tertiary rocks
than at the present day, the oldest tertiary rocks do not bring us near
the primitive form of either. If, in the same way, the convergence of the
varied forms of reptiles is measured against the time during which their
remains are preserved--which is represented by the whole of the tertiary
and mesozoic formations--the amount of that convergence is far smaller
than that of the lines of mammals between the present time and the
beginning of the tertiary epoch. And it is a broad fact that, the lower
we go in the scale of organization, the fewer signs are there of
convergence towards the primitive form from whence all must have
diverged, if evolution be a fact. Nevertheless, that it is a fact in some
cases, is proved, and I, for one, have not the courage to suppose that
the mode in which some species have taken their origin is different from
that in which the rest have originated.

What, then, has become of all the marine animals which, on the hypothesis
of evolution, must have existed in myriads in those seas, wherein the
many thousand feet of Cambrian and Laurentian rocks now devoid, or almost
devoid, of any trace of life were deposited?

Sir Charles Lyell long ago suggested that the azoic character of these
ancient formations might be due to the fact that they had undergone
extensive metamorphosis; and readers of the "Principles of Geology" will
be familiar with the ingenious manner in which he contrasts the theory of