THE OLIGOCENE 69 



The strata gradually become more marine upwards. 

 The marine beds were called by Forbes the Corbula beds, 

 from two small shells, C. pisum and C. vectensis, of which 

 some of the clays are full. Remains of early mammalia 

 are found in the Hamstead beds, the most frequent being 

 a hog-like animal, of supposed aquatic habits, Hyopo- 

 tamus, of which there are more than one species. 



The fauna and flora of the Oligocene strata show that 

 the climate was still sub-tropical, though somewhat 

 cooling down from the Eocene. Palms grew in what is now 

 the Isle of Wight. Alligators and crocodiles swam in the 

 rivers. Turtle were abundant in river and lagoon. 

 Specially interesting in the Eocene and Oligocene are the 

 mammalian remains. They show us mammals in an 

 early stage before they branched off into the various 

 families as we know them to-day. The Palaeotherium 

 was an animal like the tapir, now an inhabitant of the 

 warmer regious of Asia and America. Recent discoveries 

 in Eocene strata in Egypt show stages of development 

 between a tapir-like animal and the elephant with long 

 trunk and tusks. There were in those days hog-like 

 animals intermediate between the hogs and the hippopo- 

 tami. There were ancestors of the horse with three toes 

 on each foot. There were hornless ancestors of the deer 

 and antelopes. Many of the early mammals showed 

 characters now found in the marsupials, the order to which 

 the Kangaroo and Opossum belong, members of which 

 are found in rocks of the Secondary Era, and are the only 

 representatives of the mammalia in that age. Some of 

 the early Eocene mammalia are either marsupials, or 

 closely related to them. In the Oligocene we find the 

 mammalian life becoming more varied, and branching out 

 into the various groups we know to-day ; while the 

 succeeding Miocene Period witnesses the culmination of 

 the mammalia mammals of every family abounding all 

 over the earth's surface, in a profusion and variety not 

 seen before or since, outside the tropics. 



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