312 EOCENE PERIOD. [Ch. XXII. 



Eocene deposits originated while the chalk and other secondary 

 rocks were rising from the deep and wasting away. 



Earthquakes during the Eocene period. We have pointed 

 out, in a former chapter, our reasons for concluding that the 

 Paris basin was a theatre of subterranean convulsions during 

 the Eocene period, the older beds of the calcaire grossier 

 having been raised and exposed to the action of the waves 

 before, or at least during, the deposition of the upper or second 

 marine group *. These convulsions w r ere doubtless connected 

 with that depression which let in the sea upon the second fresh- 

 water formation, and gave rise to the superposition of the 

 upper marine beds. We have also demonstrated, in a pre- 

 ceding chapter, that some of the earlier volcanic eruptions in 

 Auvergne happened before the Eocene species of animals were 

 extinct, and we suggested that the great lakes of Central France 

 may have been drained by alterations of level which accompa- 

 nied the outbreak of those earlier Eocene volcanos of Auvergne. 

 We ought not, therefore, to be surprised if we discover proofs 

 that the south-east of England participated in the earthquakes 

 which seem to have extended at that time over a considerable 

 part of the neighbouring continent ; and we may refer the 

 alternation of marine and fresh-water beds in the Isle of Wight 



O 



and coast of Hampshire, to changes of level analogous to those 

 which gave rise to the intercalation of the upper marine for- 

 mation in the Paris basin. 



Why the English Eocene strata rise nearly as h'ujh as the 

 denuded secondary districts. Those geologists who have 

 hitherto regarded the rise and denudation of the lands in 

 the south-east of England as events posterior in date to the 

 deposition of the London clav, will object to the foregoing 

 reasoning, that not only certain outlying patches of tertiary 

 strata, but even the central parts of the London and Hamp- 

 shire basins, attain very considerable altitudes above the level 

 of the sea. Tims the London clay at Highbcach, in Essex, 

 reaches the height of 750 feet, an elevation exceeding that 

 * Si'c above, p. 248. 



