188 TERMS EOCENE, MIOCENE, AND PLIOCENE. [Ch. XIII. 



pressive of their different degrees of affinity to the living fauna. With 

 this view, I obtained information respecting the specific identity of many 

 tertiary and recent shells from several Italian naturalists, and among 

 others from Professors Bonelli, Guidotti, and Costa. Having in 1829 

 become acquainted with M. Deshayes, of Paris, already well known by 

 his conchological works, I learnt from him that he had arrived, by inde- 

 pendent researches, and by the study of a large collection of fossil and 

 recent shells, at very similar views respecting the arrangement of tertiaiy 

 formations. At my request he drew up, in a tabular form, lists of all 

 the shells known to him to occur both in some tertiary formation and in 

 a living state, for the express purpose of ascertaining the proportional 

 number of fossil species identical with the recent which characterized 

 successive groups ; and this table, planned by us in common, was pub- 

 lished by me in 1833.* The number of tertiary fossil shells examined 

 by M. Deshayes was about 3000 ; and the recent species with which they 

 had been compared about 5000. The result then arrived at was, that 

 in the lower tertiary strata, or those of London and Paris, there were 

 about 3± per cent, of species identical with recent ; in the middle ter- 

 tiary of the Loire and Gironde about 1 7 per cent. ; and in the upper 

 tertiary or Subapennine beds, from 35 to 50 per cent. In formations 

 still more modern, some of which I had particularly studied in Sicily, 

 where they attain a vast thickness and elevation above the sea, the num- 

 ber of species identical with those now living was believed to be from 

 90 to 95 per cent. For the sake of clearness and brevity, I proposed 

 to give short technical names to these four groups, or the periods to 

 which they respectively belonged. I called the first or oldest of them 

 Eocene, the second Miocene, the third Older Pliocene, and the last or 

 fourth Newer Pliocene. The first of the above terms, Eocene, is derived 

 from 7jw£, eos, dawn, and xouvo^, cainos, recent, because the fossil shells of 

 this period contain an extremely small proportion of living species, which 

 may be looked upon as indicating the dawn of the existing state of the 

 testaceous fauna, no recent species having been detected in the older or 

 secondary rocks. 



The term Miocene (from fxsiov, meion, less, and xaivog, cainos, recent) 

 is intended to express a minor proportion of recent species (of testacea), 

 the term Pliocene (from nXetov, pleion, more, and xaivog, cainos, recent) a 

 comparative plurality of the same. It may assist the memory of stu- 

 dents to remind them, that the Miocene contain a minor proportion, and 

 Pliocene a comparative plurality of recent species ; and that the greater 

 number of recent species always implies the more modern origin of the 

 strata. 



It has sometimes been objected to this nomenclature that certain spe- 

 cies of infusoria found in the chalk are still existing, and, on the other 

 hand, the Miocene and Older Pliocene deposits often contain the remains 

 of mammalia, reptiles, and fish, exclusively of extinct species. But the 



* See Princ. of Geol. vol. iii. 1st ed 



