erless other cases where the geological record does testify to
connecting links in a most satisfactory manner. For in view of this
consideration the burden of proof is thrown upon those who point to
particular cases where there is thus a conspicuous absence of
transitional forms--the burden, namely, of proving that such cases are
not due merely to a break in the record. Besides, the break in the
record as regards this particular case may be apparent rather than real.
For I suppose there is no greater authority on the pure geology of the
subject than Sir Charles Lyell, and this is what he says of the
particular case in question. "If the passage seem at present to be
somewhat sudden from the flora of the Lower or Neocomian to that of the
Upper Cretaceous period, the abruptness of the change will probably
disappear when we are better acquainted with the fossil vegetation of
the uppermost tracts of the Neocomian and that of the lowest strata of
the Gault, or true Cretaceous series[59]."

[59] _Elements of Geology_, p. 280.

Lastly, the fact of the flora of the glacial epoch not having exhibited
any modifications during the long residence of some of its specific
types in Great Britain and elsewhere, is a fact of some importance to
the general theory of evolution, since it shows a higher degree of
stability on the part of these specific types than might perhaps have
been expected, supposing the theory to be true. But I do not see that
this constitutes a difficulty against the theory, when we have so many
other cases of proved transmutation to set against it. For instance, not
to go further afield than this very glacial flora itself, it will be
remembered that in an earlier chapter I selected it as furnishing
specially cogent proof of the transmutation of species. What, then, is
the explanation of so extraordinary a difference between Mr. Carruthers'
views and my own upon this point? I believe the explanation to be that
he does not take a sufficiently wide survey of the facts.

To begin with, it seems to me that he exaggerates the vicissitudes to
which the species of plants that he calls into evidence have been
exposed while advancing before, and retreating after, the ice. Rather do
I agree with Darwin that "they would not have been exposed during their
long migrations to any great diversity of temperature; and as they all
migrated in a body together, their mutual relations will not have been
much disturbed; hence, in ac