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Our little layer of Tertiary strata on the top is, however, very important. It took several million years in forming, although it is only one-fortieth of the whole thickness of aqueous deposit on the crust of the earth. We divide it into Pliocene, Miocene, and Eocene, and each of these into upper, middle, and lower, the Eocene being the oldest.
In the first extract we have the thin end of the wedge driven a little way; in the last, the wedge driven home. We have already sketched some of the reasons suggestive of such a theory of derivation of species, reasons which gave it plausibility, and even no small probability, as applied to our actual world and to changes occurring since the latest tertiary period.
Trinidad seems to have had its full share of those later disturbances of the earth-crust, which carried tertiary strata up along the shoulders of the Alps; which upheaved the chalk of the Isle of Wight, setting the tertiary beds of Alum Bay upright against it; which even, after the Age of Ice, thrust up the Isle of Moen in Denmark and the Isle of Ely in Cambridgeshire, entangling the boulder clay among the chalk how long ago?
The long and interesting story of the mammals must be told in a separate chapter, and a further chapter must be devoted to the appearance of the human species. We saw that the Angiosperms, or flowering plants, appeared at the beginning of the Cretaceous period, and were richly developed before the Tertiary Era opened. We saw also that their precise origin is unknown.
From these facts, and from the generic resemblance of the fossils from the different localities, I cannot avoid the suspicion that they all belong to nearly the same epoch, which epoch, as we shall immediately see, must be a very ancient tertiary one.
The greater the difficulties by which he is confronted, the more gnawing becomes the Englishman's, hunger for action. "Something must be done!" is his instinctive cry when dangers or perplexities arise, and he is feverishly eager to do it. What exactly "it" should be, and how it may be most wisely done, are secondary, and even tertiary, considerations.
In the majority of cases the child recovers from these early manifestations, especially when efficiently treated, and may enjoy an indefinite period of good health. On the other hand, when it attains the age of from two to four years, it may begin to manifest lesions which correspond to those of the tertiary period of acquired syphilis.
We have seen that the highly remarkable fact of the absence of any EXTENSIVE formations containing recent shells, either on the eastern or western coasts of the continent, though these coasts now abound with living mollusca, though they are, and apparently have always been, as favourable for the deposition of sediment as they were when the tertiary formations were copiously deposited, and though they have been upheaved to an amount quite sufficient to bring up strata from the depths the most fertile for animal life can be explained in accordance with the above proposition.
These wide step-formed plains have been formed by the denuding action of the coast-waves on the old tertiary strata; and therefore, when the surface of the 350 feet plain, with the shells on it, first rose above the level of the sea, the 250 feet plain did not exist, and its formation, as well as the spreading out of the gravel on its summit, must have taken place subsequently.
Such a shrinkage and eruption made the Hawaiian Islands, probably in Tertiary times; such a shrinkage may make other islands and other continents before another period of equal time has elapsed.
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