( loo ) 



ERA OF THE TERTIARY FOR]\IATION. 



MAMMALIA ABUNDANT. 



The chalk-beds are the highest Avhich extend over a 

 considerable space ; but in hollows of these beds, com- 

 paratively limited in extent, there have been formed 

 series of vstrata — clays, limestones, marls, alternating — to 

 which the name of the Terfiarij Formation has been 

 applied. London and Paris alike rest on basins of this 

 formation, and another such basin extends from near 

 Winchester, under Southampton, and re-appears in the 

 Isle of Wight. A stripe of it extends along the east coast 

 of North America, from Massachusetts to Florida. It is 

 also found in Sicily and Italj^, insensibly blended with 

 formations still in progress. Though comparatively a 

 local formation, it is not of the less importance as a record 

 of the condition of the earth during a certain period. As 

 in other formations, it is marked, in the most distant, 

 localities, by identity of organic remains. 



The hollows filled by the . tertiary formation nnist bo 

 considered as the beds of estuaries left at the conclusion 

 of the ci-etaceous period. We have seen that an estuary, 

 either by the drifting up of its mouth, or a change of 

 level in that quarter, may be supposed to have become 

 an inland sheet of water, and that, by another change, 

 of the reverse kind, it may be supposed to have become 



