290 ZOOLOGICAL GEOGRAPHY. [part hi. 



carnivora had reached it ; and we consequeutly find there, no 

 wholly terrestrial form of bird but the gigantic and powerful 

 jMpyornis, well able to defend itself against such enemies. As 

 already intimated, we refer the South American element in 

 Madagascar, not to any special connection of the two countries 

 independently of Africa, but to . the preservation there of a 

 number of forms, some derived from America through Africa, 

 others of once almost cosmopolitan range, but which, owing to the 

 severer competition, have become extinct on the African con- 

 tinent, while they have continued to exist under modified forms 

 in the two other countries. 



The depths of all the great oceans are now known to be so 

 profound, that w^e cannot conceive the elevation of their beds 

 above the surface without some corresponding depression else- 

 where. And if, as is probable, these opposite motions of the 

 earth's crust usually take place in parallel bands, and are to 

 some extent dependent on each other, an elevation of tlie sea 

 bed could hardly fail to lead to the submergence of large tracts 

 of existing continents ; and tliis is the more likely to occur on 

 account of the great disproportion that we have seen exists 

 between the mean heiglit of the land and the mean depth of the 

 ocean. Keeping this principle in view, we may, with some 

 probability, suggest the successive stages by which the Ethiopian 

 region assumed its present form, and acquired the striking 

 peculiarities that characterise its several sub-regions. During 

 the early period, when the rich and varied temperate flora of the 

 Cape, and its hardly less peculiar forms of insects and of low type 

 mammalia, were in process of development in an extensive 

 south temperate land, we may be pretty sure tliat the whole of 

 the east and much of the north of Africa was deep sea. At a 

 later period, when this continent sank towards the south and 

 east, the elevation may have occurred which connected ]\[ada- 

 gascar with Ceylon ; and only at a still later epoch, when the 

 Indian Ocean had again been formed, did central, eastern, and 

 northern Africa gradually rise above the ocean, and effect a 

 connection with tlie great northern continent by way of Abys- 

 sinia and Arabia. And if this last change took place with 



