The Elements of Geology eBook

This eBook from the Gutenberg Project consists of approximately 384 pages of information about The Elements of Geology.

Life of the Permian.  The close of the Paleozoic was, as we have seen, a time of marked physical changes.  The upridging of the Appalachians had begun and a wide continental uplift—­proved by the absence of Permian deposits over large areas where sedimentation had gone on before—­opened new lands for settlement to hordes of air-breathing animals.  Changes of climate compelled extensive migrations, and the fauna of different regions were thus brought into conflict.  The Permian was a time of pronounced changes in plant and animal life, and a transitional period between two great eras.  The somber forests of the earlier Carboniferous, with their gigantic club mosses, were now replaced by forests of cycads, tree ferns, and conifers.  Even in the lower Permian the Lepidodendron and Sigillaria were very rare, and before the end of the epoch they and the Calamites also had become extinct.  Gradually the antique types of the Paleozoic fauna died out, and in the Permian rocks are found the last survivors of the cystoid, the trilobite, and the eurypterid, and of many long-lived families of brachiopods, mollusks, and other invertebrates.  The venerable Orthoceras and the Goniatite linger on through the epoch and into the first period of the succeeding era.  Forerunners of the great ammonite family of cephalopod mollusks now appear.  The antique forms of the earlier Carboniferous amphibians continue, but with many new genera and a marked increase in size.

A long forward step had now been taken in the evolution of the vertebrates.  A new and higher type, the reptiles, had appeared, and in such numbers and variety are they found in the Permian strata that their advent may well have occurred in a still earlier epoch.  It will be most convenient to describe the Permian reptiles along with their descendants of the Mesozoic.



With the close of the Permian the world of animal and vegetable life had so changed that the line is drawn here which marks the end of the old order and the beginning of the new and separates the Paleozoic from the succeeding era,—­the Mesozoic, the Middle Age of geological history.  Although the Mesozoic era is shorter than the Paleozoic, as measured by the thickness of their strata, yet its duration must be reckoned in millions of years.  Its predominant life features are the culmination and the beginning of the decline of reptiles, amphibians, cephalopod mollusks, and cycads, and the advent of marsupial mammals, birds, teleost fishes, and angiospermous plants.  The leading events of the long ages of the era we can sketch only in the most summary way.

The Mesozoic comprises three systems,—­the Triassic, named from its threefold division in Germany; the jurassic, which is well displayed in the Jura Mountains; and the Cretaceous, which contains the extensive chalk (Latin, creta) deposits of Europe.

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The Elements of Geology from Project Gutenberg. Public domain.
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