The Classification of the Tertiary Period by means of the Mammalia

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Abstract
1. Introduction . T he . classification of the Tertiary, or the third of the great life-periods, sketched in outline more than fifty years ago, and since then altered in no important degree, seems to me not to be in harmony with our present knowledge; and the definitions of the series of events which took place in it have been materially modified by recent discoveries in various parts of the world. The terms Eocene, Miocene, and Pliocene* no longer express the idea of percentages of living species on which they were based, and Quaternary, Post-Tertiary, and Recent are founded on an assumed great break in the life-history between the present day and the Tertiary period, comparable to that which separates the Secondary from the Tertiary or the Primary periods, a break which has been disproved by more recent inquiries. It has therefore seemed to me opportune to lay before the Society the results of the investigations which I have carried on for some years into these questions, and to propose a classification of the Tertiary period of Europe by appealing to the Mammalia, by applying the same method by which the Pleistocene and the Prehistoric periods have already been defined*. 2. The Value of Invertebrates and Vertebrates in Classification . The Eocene, Miocene, and Pliocene divisions of the Tertiary period are based upon the varying percentages of living Mollusca in a comparison of three thousand fossil with five thousand living forms ; and the term Pleistocene† was subsequently invented to imply a nearer approximation

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