344 
DARWINISM 
CHAP. 
Now the whole series of marine stratified rocks, from the 
earliest Palaeozoic to the most recent Tertiary beds, consist of 
materials closely corresponding to the land debris now being 
deposited within a narrow belt round the shores of all con- 
' tinents; while no rocks have been found which can be identified 
with the various oozes now forming in the deep abysses of the 
ocean. It follows, therefore, that all the geological formations 
have been formed in comparatively shallow water, and always 
adjacent to the continental land of the period. The great 
thickness of some of the formations is no indication of a deep 
sea, but only of slow subsidence during the time that the 
deposition was in progress. This view is now adopted by 
many of the most experienced geologists, especially by Dr. 
Archibald Geikie, Director of the Geological Survey of Great 
Britain, who, in his lecture on “ Geographical Evolution,” says : 
“From all this evidence we may legitimately conclude that 
the present land of the globe, though consisting in great 
measure of marine formations, has never lain under the deep 
sea ; but that its site must always have been near land. Even 
its thick marine limestones are the deposits of comparatively 
shallow water.” 1 
But besides these geological and physical considerations, 
there is a mechanical difficulty in the way of repeated 
change of position of oceans and continents which has not 
yet received the attention it deserves. According to the 
recent careful estimate by Mr. John Murray, the land area 
of the globe is to the water area as - 28 to •72. The mean 
height of the land above sea-level is 2250 feet, while the 
mean depth of the ocean is 14,640 feet. Hence the bulk 
of dry land is 23,450,000 cubic miles, and that of the waters 
of the ocean 323,800,000 cubic miles; and it follows that if 
the whole of the solid matter of the earth’s surface were 
reduced to one level, it would be everywhere covered by an 
ocean about two miles deep. The accompanying diagram will 
serve to render these figures more intelligible. The length of 
the sections of land and ocean are in the proportion of their 
respective areas, while the mean height of the land and the 
mean depth of the ocean are exhibited on a greatly increased 
1 I have given a full summary of the evidence for the permanence of 
oceanic and continental areas in my Island Life, chap. vi. 
