346 
DARWINISM 
CHAP. 
above the surface could occur without an equivalent depression 
elsewhere. The fact that the waters of the ocean are sufficient 
to cover the whole globe to a depth of two miles, is alone 
sufficient to indicate that the great ocean basins are permanent 
features of the earth’s surface, since any process of alterna¬ 
tion of these with the land areas would have been almost 
certain to result again and again in the total disappearance of 
large portions, if not of all, of the dry land of the globe. But 
the continuity of terrestrial life since the Devonian and Car¬ 
boniferous periods, and the existence of very similar forms in 
the corresponding deposits of every continent—as well as the 
occurrence of sedimentary rocks, indicating the proximity of 
land at the time of their deposit, over a large portion of the 
surface of all the continents, and in every geological period— 
assure us that no such disappearance has ever occurred. 
Oceanic and Continental Areas. 
When we speak of the permanence of oceanic and conti¬ 
nental areas as one of the established facts of modern research, 
we do not mean that existing continents and oceans have 
always maintained the exact areas and outlines that they now 
present, but merely, that while all of them have been under¬ 
going changes in outline and extent from age to age, they 
have yet maintained substantially the same positions, and 
have never actually changed places with each other. There 
are, moreover, certain physical and biological facts which 
enable us to mark out these areas with some confidence. 
We have seen that there are a large number of islands 
which may be classed as oceanic, because they have never 
formed parts of continents, but have originated in mid-ocean, 
and have derived their forms of life by migration across the 
sea. Their peculiarities are seen to be very marked in com¬ 
parison with those islands which there is good reason to 
believe are really fragments of more extensive land areas, and 
are hence termed “continental.” These continental islands 
consist in every case of a variety of stratified rocks of various 
ages, thus corresponding closely with the usual structure of 
continents; although many of the islands are small like 
Jersey or the Shetland Islands, or far from continental 
land like the Falkland Islands or New Zealand. They all 
