INTRODUCTION, xvi 
and Suffolk to the North Downs, the other from the South 
Downs, along the range of chalk hills, into Dorsetshire. 
Some parts of these deposits attain the height of more than 
one thousand feet, indicating the great depth of the ocean 
into which they were poured.* 
At the time when these vast but gradual operations 
were taking place, an arm of sea extended from the 
north to the area called the Basin of Paris, which received 
the overflow of a chain of lakes extending thither from 
the highest part of the central mountain group of France.+ 
An enormous mass of mixed or alternating marine and 
freshwater deposits was accumulated in this basin, coeval, 
if we may judge from the identity of the species of shells, 
with the outpouring of the London and plastic clays upon 
the English chalk. Each division of the French eocene 
deposits is characterised either by the exclusive possession 
or the predominance of particular fossils, and the entire 
series must have required a long lapse of ages for its accu- 
mulation. 
Yet the sudden introduction, as it seems, of various 
forms of Mammalia, at this period of the earth’s history, 
corroborates the inference, from more direct evidence, of 
the long interval of time that elapsed between the ces- 
sation of the British chalk formation, and the ‘commence- 
ment of the tertiary deposits. 
The proofs of the abundant Mammalian inhabitants of 
the eocene continent were first obtained by Cuvier from the 
fossilized remains in the deposits that fill the enormous 
Parisian excavation of the chalk. But the forms which 
that great Anatomist restored were all new and strange, 
—specifically, and for the most part generically, distinct 
* Lyell, ‘ Principles of Geology,’ vol. iv. ch. xx. and xxi. 
+ Omalius d’Halloy, cited by Lyell, 1. c. p. 165. 
b 
