216 
ELEMENTS OF GEOLOGY. 
ever alFord sufficient data for determining even genera and 
families in the vegetable kingdom. -In truth, before such 
remains could be rendered available a new science had to 
be created. It was necessary to study the outlines, nerva¬ 
tion, and microscopic structure of the leaves, with a degree 
of care which had never been called for in the classification 
of living plants, where the flower and fruit afforded charac-’ 
ters so much more definite and satisfactory. As geologists, 
we can not be too grateful to those who, instead of despair¬ 
ing when so difficult a task was presented to them, or being 
discouraged when men of the highest scientific attainments 
treated the fossil leaves as worthless, entered with full faith 
and enthusiasm into this new and unexplored field. That 
they should frequently have fallen into errors was unavoid¬ 
able, but it is remarkable, especially if we inquire into the 
history of Professor Heer’s researches, how often early con¬ 
jectures as to the genus and family founded on the leaves 
alone were afterwards confirmed when fuller information 
was obtained. As examples to be found on comparing 
Heer’s earlier and later works, I may instance the chestnut, 
elm, maple, cinnamon, magnolia, buckbean or Menyanthes, 
vine, buckthorn [Hhamnus)^ Andromeda and Myrica^ and 
among the conifers Sequoia and Taxodium, In all these 
cases the plants were first recognized by their leaves, and 
the accuracy of the determination was afterwards confirmed 
when the fruit, and in some instances both fruit and flower, 
were found attached to the same stem as the leaves. 
But let us suppose that no fruit, seed, or flower had ever 
been met with in a fossil state, we should still have been in¬ 
debted to the persevering labors of botanical palaeontologists 
for one of the grandest scientific discoveries for which the 
present century is remarkable—namely, the proofs now es¬ 
tablished of the prevalence of a mild climate and a rich ar¬ 
borescent flora in the arctic regions in that Miocene epoch 
on the history of which we are now entering. It may be 
useful if I endeavor to give the reader in a few words some 
idea of the nature of the evidence of these important conclu¬ 
sions, to show how far they may be safely based on fossil 
leaves alone. When we begin by studying the fossils of the 
I^^ewer Pliocene deposits, such as those of the Upper Val 
d’Arno, before alluded to, we perceive that the fossil foliage 
agrees almost entirely with the trees and shrubs of a mod¬ 
ern European forest. In the plants of the Older Pliocene 
strata of the same region we observe a larger proportion of 
species and genera which, although they may agree with 
well-known Asiatic or other foreign types, are at present 
