INTRODUCTION. XVII 



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. 

 t Omalius d'Halloy, cited by Lyell, 1. c. p. 165. 



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