273 PHYSICAL GEOGRAPHY. 



buted, together with other causes, to equalise climates, p,nd 

 to maintain a high temperature. It is only necessary to 

 add here, in reference to the progressive extension of 

 dry land, that a short time before the cataclysms which, 

 at longer or shorter intervals, caused the destruction 

 of so many gigantic vertebrated animals, part of the conti- 

 nental masses presented the same divisions as at present. 

 There prevails, both in South America and in Australia, a 

 great analogy between the living animals and the extinct 

 species of those countries Fossil species of Kangaroo have 

 been discovered in New Holland ; and in New Zealand, the 

 semi-fossilized bones of a gigantic struthious bird, the 

 Dinonris of Owen, closely allied to the present Apteryx of 

 the same islands, and remotely so to the recently extinct 

 Dodo of the island of Rodriguez. 



A considerable part of the height of the present continents 

 above the surrounding waters may perhaps be due to the erup- 

 tion of the quartzose porphyry, which overthrew with violence 

 the first great terrestrial flora, the material of our coal-beds. 

 The level portion of our continents, to which we give the 

 name of plains, are the broad summits of mountains, of 

 which the feet are at the bottom of the ocean : considered in 

 respect to submarine depths, these plains are elevated pla- 

 teaus, of which the original inequalities have been partially 

 filled up by horizontal layers of later sedimentary deposits, 

 and covered over with alluvium. 



Amongst the leading considerations in this part of the 

 general contemplation of nature, we must regard, first, the 

 quantity of land raised above the water ; next the configu- 

 ration of each great continental mass in horizontal extension 



