4 DEFINITION OF THE TERMS CHAP. i. 



was, that in the lower tertiary strata there were about 3'. 

 j)er cent, identical with recent; in the middle tertiary (the 

 faluns of the Loire and Gironde), about 17 j)er cent. ; and in 

 the upper tertiary, from 35 to 50, and sometimes in the most 

 modern beds as much as 90 to 95 per cent. For the sake of 

 clearness and brevity, I proposed to give short technical names 

 to these sets of strata, or the periods to which they respect- 

 ively belonged. I called the first or oldest of them Eocene, 

 the second Miocene, and the third Pliocene. The first of 

 the above terms, Eocene, is derived from ifd)': eos, dawn, and 

 xaivoq kainos, recent; because an exti'emely small propor- 

 tion of the fossil shells of this period could be referred to 

 living species, so that this era seemed to indicate the dawn of 

 the present testaceousfauna, no living species of shells having 

 been detected in the antecedent or secondary rocks. 



Some conchologists are now unwilling to allow that any 

 Eocene species of shell has really survived to our times so 

 mialtered as to allow of its specific identification with a living 

 species. I cannot enter in this place into this wide controversy. 

 It is enough at present to remark that the character of the 

 Eocene fauna, as contrasted with that of the antecedent 

 secondary formations, wears a very modern aspect, and that 

 some able living conchologists still maintain that there are 

 Eocene shells not specifically distinguishable from those now 

 extant; though they may be fewer in number than was 

 supposed in 1833. 



The term Miocene (from /iscujv vicion, less, and x.atv6<; 

 kainos, recent) is intended to express a minor proportion of 

 recent species (of testacea) ; the term Pliocene (from Tihicuv 

 pleion, more, and xaT^oc kainos, recent), a comparative 

 plurality of the same. 



It has sometimes been objected to this nomenclature that 

 certain species of infusoria found in the chalk are still 

 existing, and, on the other hand, the Miocene and Older 



