CENOZOIC ERA: AGE OF MAMMALS 577 



Eocene as that of North America. Seas covered large areas that are 

 now land, and there were probably extensive land masses which are 

 now covered by the ocean. Europe was smaller than at present and 

 at times was entirely separated from Asia by a narrow sea on the 

 east side of the Ural Mountains. The most marked feature of the 

 Eocene European continent was the greatly expanded Mediterranean 

 Sea which, with its extensive arms, covered the sites of the conspicu- 

 ous mountains of the present : the Pyrenees, Apennines, Alps, and 

 Urals. Above the surface of this sea numerous islands probably stood 

 on the sites of some of the ranges. The greater part of Spain seems 

 to have been separated for a time from the mainland by a sea which 

 also covered a portion of southern France. 



Not only Europe, but Asia and Africa as well, were far from having 

 attained their present outlines. The greater part of Africa north of 

 the equator was under water, and an extension of the Mediterranean 

 Sea reached to the Indian Ocean. Portions of Australia, New Zea- 

 land, Patagonia, and the West Indies were also submerged. 



In portions of Europe and Africa a great thickness of limestone, 

 made up of large Foraminifera (nummulites, p. 626), was deposited ; 

 besides which, an immensely thick mass of sandstone and shale which 

 now outcrops on the Alps was also laid down. The nummulitic lime- 

 stone was largely used in the construction of the pyramids of Egypt. 

 The Eocene strata have since been raised to great heights, as is indi- 

 cated by their presence on the Tibet Plateau at an altitude of 20,000 

 feet, in the Himalayas 16,000 feet above the sea, as well as high up on 

 the Alps, Pyrenees, Caucasus, and other mountain ranges. 



It will be seen from the above imperfect history that the outlines 

 and mountainous regions of Europe and Asia were very different 

 during the Eocene from what they are to-day. 



Oligocene 



The Oligocene, which followed the Eocene, is sometimes included in 

 the latter, but is usually separated from it because of the distinctness 

 of the two series in Europe, and also because they can be readily 

 separated in North America whenever fossils occur. 



Atlantic and Gulf Coasts. — The Oligocene does not have a wide 

 distribution on the Atlantic coast, but is well represented in the Gulf 

 region, where 2000 feet of strata, rich in marine invertebrates, occur. 

 The Oligocene in these regions rests upon the Eocene without a break, 

 the two series being distinguished by a change in fauna. A great de- 



