324 TROPICAL NATURE, AND OTHER ESSAYS. 



leopards, and hyaenas, the zebras, giraffes, buffaloes, 

 and antelopes, the elephants, rhinoceroses, and hippo- 

 potami, and perhaps even the numerous monkeys, 

 baboons, and anthropoid apes, are every one of them 

 comparatively recent immigrants, who took possession of 

 the country as soon as an elevation of the old Eocene 

 and Miocene sea-bed afforded a passage from the southern 

 borders of the Palsearctic region. This event probably 

 occurred about the middle of the Miocene period, and 

 it must have effected a vast change in the fauna of 

 Africa. A number of the smaller and more defenceless 

 of the ancient inhabitants must have been soon exter- 

 minated, as surely as our introduced pigs, dogs, and 

 goats, exterminate so many of the inhabitants of 

 oceanic islands ; while the new comers finding a country 

 of immense extent, with a tropical climate, and not too 

 much encumbered with forest vegetation, spread rapidly 

 over it, and thenceforth, greatly multiplying, became 

 more or less modified in accordance with the new condi- 

 tions. We shall find that this theory not only accounts 

 for the chief specialities, but also explains many of the 

 remarkable deficiencies of the Ethiopian fauna. Thus, 

 bears and deer are absent, because they are compara- 

 tively late developments, and were either unknown or 

 rare in Europe till late Miocene or Pliocene times ; 

 while, on the other hand, the immense area of open 

 tropical country in Africa has favoured the preservation 

 of numerous types of large mammalia which have 

 perished in the deteriorated climate and diminished area 

 of Europe. 



Our knowledge of the geology of Africa is not suffi- 

 ciently detailed to enable us to determine its earlier 



