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 Nummulitic 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, 
