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. 



