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Updated: May 31, 2025
Where the imputed forefathers lived, their relatives and supposed descendants now flourish. All the actual classes of the animal and vegetable kingdoms were represented in the tertiary faunas and floras, and in nearly the same proportions and the same diversities as at present.
Subject to these allowances, the fauna of each geological period undoubtedly is intermediate in character, between the preceding and succeeding faunas.
But each fauna is not necessarily exactly intermediate, as unequal intervals of time have elapsed between consecutive formations. It is no real objection to the truth of the statement that the fauna of each period as a whole is nearly intermediate in character between the preceding and succeeding faunas, that certain genera offer exceptions to the rule.
The evolutionary hypothesis here advocated also serves to explain all those remarkable facts which were stated in the first chapter to be explicable by the theory of Natural Selection, namely, the relation of existing to recent faunas and floras; the phenomena of homology and of rudimentary structures; also the processes gone through in development; and lastly, the wonderful facts of mimicry.
The mapping out of extinct faunas and floras and assigning pedigree to existing species are by no means the whole province of geologists. Productive industry owes to them a vast saving of time and cost in searching for useful minerals. They distinguish the same strata in widely separated districts by means of the characteristic fossils, and are thus enabled to guide the miner.
So that no one deposit near our shores can contain anything like a true representation of the Fauna of the surrounding sea; much less of the co-existing Faunas of other seas in the same latitude; and still less of the Faunas of seas in distant latitudes.
In the southern hemisphere, if we compare large tracts of land in Australia, South Africa, and western South America, between latitudes 25 and 35 degrees, we shall find parts extremely similar in all their conditions, yet it would not be possible to point out three faunas and floras more utterly dissimilar.
On the other hand, proceeding still further westward from the eastern islands of the tropical parts of the Pacific, we encounter no impassable barriers, and we have innumerable islands as halting-places, or continuous coasts, until after travelling over a hemisphere we come to the shores of Africa; and over this vast space we meet with no well-defined and distinct marine faunas.
In this Archipelago there are two distinct faunas rigidly circumscribed, which differ as much as those of South America and Africa, and more than those of Europe and North America: yet there is nothing on the map or on the face of the islands to mark their limits. The boundary line often passes between islands closer than others in the same group.
On the other hand, proceeding still further westward from the eastern islands of the tropical parts of the Pacific, we encounter no impassable barriers, and we have innumerable islands as halting-places, until after travelling over a hemisphere we come to the shores of Africa; and over this vast space we meet with no well-defined and distinct marine faunas.
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