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I cannot, however, think that botanical evidence of such a nature is sufficient to warrant a satisfactory reference of these Indian coal-fields to the same epoch as those of England or of Australia; in the first place the outlines of the fronds of ferns and their nervation are frail characters if employed alone for the determination of existing genera, and much more so of fossil fragments: in the second place recent ferns are so widely distributed, that an inspection of the majority affords little clue to the region or locality they come from: and in the third place, considering the wide difference in latitude and longitude of Yorkshire, India, and Australia, the natural conclusion is that they could not have supported a similar vegetation at the same epoch.
It was necessary to study the outlines, nervation, 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 characters so much more definite and satisfactory.
The term "nerves" still persists, in the old sense, in both botany and entomology, which speak of the "nerves" of a butterfly's wing, or the "nervation" of a leaf, meaning simply the branching, fibrous framework of each. It comes in the nature of a surprise to most of us to learn that "nerves" are real things. I shall never forget the shock of my own first convincing demonstration of this fact.
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