INTRODUCTION. 15 
mation distinct in its characters from the London Clay 
below, and the English Crag above it. In it, M. Deshayes 
has observed one thousand and twenty-one species, one 
hundred and seventy-six of which, only, are found ina 
recent state. 
Superior again to this, in the Pliocene period, we find 
the recent species comparatively abundant. Mr Lyell in 
dividing this into the Older and Newer Pliocene, observes, 
that “the plurality of living species is so very decided.” 
The former includes the Subappennine hills, and the En- 
glish Crag; the latter, the Sicilian beds. 
It has been stated that forty-five hundredths of the spe- 
cies found in the English Crag exist in a recent state ;* 
while in the Sicilian beds, according to Mr Lyell, ten only 
out of two hundred and twenty-six are extinct or un- 
known, nearly the whole of them existing at the present 
time in the neighbouring seas. 
In addition to the marine reliquiz, the remains of terres- 
trial mammiferous animals afford us, in the Tertiary Form- 
ation, a striking proof of the extraordinary change which 
has taken place. Of the numerous species the remains 
of which are there found, none now exist. ‘More than 
forty of these Eocene mammifers, are referable to a division 
of the order Pachydermata, which has now only four living 
representatives on the globe ; of these, not only the species, 
but the genera, are distinct from any of those which have 
been established for the classification of living animals.” 
The Mammalia of the Miocene agree in some of the 
genera with recent animals, and those of the Pliocene 
are “an intermixture of extinct and recent species of 
quadrupeds.” $ 
Superior, and next to the Tertiary, is De la Beche’s 
Erratic Block Group, and above it, his Modern Group. 
* Address of the Pres. of the Geo. Soc. 1833. 
t Principles of Geology, vol. 3, p. 59. 
{ Principles of Geology, vol. 3, p. 60. 
