124 MOSTLY MAMMALS 



are good reasons for regarding a large part of the basin 

 of the South Atlantic as of no great antiquity, while the 

 area of the Indian Ocean seems to have been considerably 

 enlarged during the later geological epochs. Apparently, 

 therefore, the great extent of ocean at present characteristic 

 of the southern hemisphere is a relatively modern feature. 



Hence it is clear that the extreme views prevalent a few 

 years ago as to the absolute permanency of the existing 

 continental and oceanic areas stand in need of some 

 degree of modification. And what we have now to avoid 

 is that the pendulum should not once more take too long 

 a swing in the opposite direction. 



So far as the great continental masses of the northern 

 hemisphere are concerned, it would appear that portions 

 of these have always existed to a greater or lesser extent 

 as land. But the great extent and homogeneous character 

 of formations like the Mountain Limestone, the Chalk, and 

 the NummuUtic Limestone, suggest that sea was much 

 more prevalent in this area than it is at present, and that, 

 so far as the Old World is concerned, the continental area 

 has been growing. The North Atlantic, and probably also 

 the North Pacific, may apparently be regarded as basins 

 of great antiquity. On the other hand, in the southern 

 hemisphere, although Africa, parts of Australia, and at 

 least some portions of South America, are evidently land 

 surfaces of great antiquity, they, together with the islands 

 of the Coral Sea, seem to be mere remnants of a much 

 more extensive southern continent or continents. Con- 

 versely the southern oceans have gained in area by swallow- 

 ing up these long-lost lands. Obviously, then, although 

 true in a degree, continental permanency has not been 

 the only factor in the evolution of the present surface of 

 the globe, 



