THE TERTIARY EPOCH. 
347 
proceed also, until the whole of the chalk strata 
were carried away, and the Wealden beds in their 
turn became exposed to the same destructive 
agency, ddie debris of both formations would 
thus become intermixed and deposited in the 
hollows of the chalk, giving rise to those accumula- 
tions of transported materials of which the tertiary 
strata are jirincipally composed. During these im- 
portant and extensive changes, the tertiary ocean 
which then covered the south-east of England 
must have been studded with islands, formed by 
the most elevated portions of the chalk and 
Wealden* ; the marshes of the then existing con- 
tinent were peopled with tribes of extinct animals 
allied to the Tapir (the pal<Potherians\ and the 
lacustrine formations of Hampshire and the Isle 
of ^^dght were deposited. 
The organic remains of the tertiary epoch differ 
entirely from those of the chalk upon which in 
the south-east of England they repose. In the 
Isle of Wight, in the Paris Basin, and many con- 
temporaneous deposits on the continent, they con- 
sist of alternations of marine and freshwater shells, 
indicating the existence of lakes communicating 
with the sea. The ammonites, and other ancient 
pelagian shells entirely disappear, and a small pro- 
portion of recent species occurs in the most an- 
cient, and a much more considerable number in 
the newer deposits. With these are associated the 
* Vide the “ Principles of Geology,” vol. ii. In the map illustrating 
the extent of the tertiary sea, or seas, it will be seen that Mr. Lyell 
has delineated a range of chalk islands in the south-eastern part of 
England, agreeably to this theory of the gradual elevation of the land. 
