Having alluded to the threefold division of this series of rocks, we shall proceed to notice them, dwelling a while upon each, and showing the principle on which each is based, as originated and enunciated by Lyell. Of the three divisions, the first is called _Eocene_ (_ēōs_, the dawn, and _kainŏs_, recent), by which term is represented the oldest or lowest of this tripartite series. Then we have the _Miocene_ (_meiōn_, less, and _kainŏs_, recent)—a name, we think, not the most appropriate, and likely to mislead the beginner, because really it represents a series of beds, _more_ and not _less_ recent than the _Eocene_; but the idea of the name is this (and it must be carefully borne in mind), that although it is _more_ recent than the series of beds _below_, it is _less_ recent than those _above_; it is nearer the “dawn” of our present era than the _Eocene_, but not so near the dawn as the _Pliocene_. This last term, the _Pliocene_ (from _pleiōn_, more, and _kainŏs_, recent), is applied to the newest of the beds of the tertiary series in which there are found many _more recent_ than extinct shells. The Tertiary system or series, then, is divided into these three sections: viz. 1. The older Tertiary or Eocene; 2. The middle Tertiary or Miocene; and 3. The newer Tertiary or Pliocene. We used a term just now, in quoting from Mr. Juke’s most useful manual, which we will explain; we said, the “distinction between the secondary and tertiary rocks is wholly a _palæontological_ one;” that is, it is a distinction founded not on the character of the rocks, but on the character of the _organic remains_ found in the rocks. “This character,” says Sir Charles Lyell, “must be used as a criterion of the age of a formation, or of the contemporaneous origin of two deposits in different places, under very much the same restrictions as the test of mineral composition. “First, the same fossils may be traced over wide regions, if we examine strata in the direction of their planes, although by no means for indefinite distances.