CHANGES IN LAND AND SEA 329 



but one or two species occur in New Zealand ; and the same is 

 true of Calceolaria. The evergreen beech forests of New Zealand 

 must be extraordinarily like those which Darwin described in 

 Patagonia. Even the same curious genus of fungus (Cyttaria) 

 is found on the beech trees in South America, New Zealand and 

 Tasmania. A fresh water lamprey, Geotria, also occurs both in 

 New Zealand and South America and similar cases could be 

 quoted from the invertebrate fauna. 



It is very doubtful, however, whether such an extensive change 

 in the configuration of the earth's surface as the submergence of 

 an entire continent has ever taken place. According to 

 Dr. Wallace, who is recognized as tbe greatest authority on 

 tlie subject of geographical distribution, the existing continents 

 and oceans as a whole are permanent features, although their 

 outlines may be greatly affected by oscillations of the earth's 

 crust. 



Perhaps the strongest argument against the former existence 

 of continents where we now have oceans lies in the fact that the 

 average depth of the sea is many times greater than the average 

 height of the land, no less than twelve thousand feet as com- 

 pared with one thousand, for the great depths of the ocean 

 extend over vast areas while the greatest heights of the land 

 are narrow mountain ranges. Hence, although large areas of 

 land might be submerged by a comparatively slight change of 

 level, it would take an enormous movement to bring any extensive 

 tract of the ocean bed to the surface. 



In short, we are only justified in postulating the former 

 existence of land in places where the ocean is comparatively 

 shallow, but even this limitation leaves abundant opportunity 

 for changes in the relative distribution of land and sea which 

 would profoundly aflect the distribution of plants and animals. 

 The actual occurrence of such changes is abundantly proved by 

 geological evidence and they are known to be going on at the 

 present day in many parts of the world. 



There is good reason to believe that the principal groups of 

 terrestrial animals originated in the great northern land masses 

 and that the southern peninsular areas of Africa, Australasia 

 (now, of course, represented by detached islands) and South 

 America have been peopled mainly by successive waves of 

 migration from the north. We find in all these southern areas 

 primitive, ancient forms of life. Marsupials at the present day 



