14 INTRODUCTION. 
are found so high up as the London Clay ; and to the de- 
posits superior to this, the genus is entirely wanting. Nearly 
the same observations extend to the genera Orthocera, 
Belemnites and Hamites. We look to the Tertiary Forma- 
tion with peculiar interest, as its lower deposit or period 
contains the incipient state, or as Mr Lyell says, “the 
dawn of the existing state of the animate creation.” 
The division of the Tertiary Formation into three epochs, 
has been admitted by most modern geologists. For these, 
Mr Lyell* proposes, in the descending order, the names of 
Pliocene period, Miocene period, and Eocene period. The 
first is derived from the Greek words 7aeay major, and xasves 
recens, as most of them are recent species, and of course, 
of later deposit. This he subdivides into the Newer and 
Older Pliocene, in which division M. Deshayes does not 
agree with him. The second, Miocene, is from «ay 
minor, and xx«es recens, there being here a minority of 
recent species. The third, the Eocene, is derived from iws 
aurora, and xxv; recens, this being “the dawn of the 
existing state of the animate creation.” 
In the lowest of these, the Eocene period,t there have 
been observed in Europe one thousand two hundred and 
thirty-eight species, of which the very small number of 
forty-two have been identified with recent species. ‘ Of 
fossil species, not known as recent, forty-two are common 
to the Eocene and Miocene epochs.”{ It is remarkable, 
too, that the living species are rarely inhabitants of the 
shores of those countries in which they are found in a 
fossil state, inhabiting now more southern climates. 
The next period of deposit, that of the Miocene, is a for- 
* Principles of Geology, vol. 3, p. 53. 
t Mr. Lyell, with great propriety, includes in this period the Plastic 
Clay with the London Clay; the line of separation of which, he says, 
“is quite arbitrary.” Principles of Geology, vol. 3, p. 278. 
t Principles of Geology, vol. 3, p. 55. 
