324 NATURE AND MAN. 



present bed of the North Atlantic has ever been raised into dry 

 land since the termination of the Cretaceous epoch, which was 

 marked by the elevation of the chalk formations of Europe and 

 Asia on the one side, and of North America on the other, into 

 dry land ; and that the persistence of a considerable number of 

 cretaceous types in its marine fauna justifies the conclusion that 

 the deep sea-bed of this ocean has not undergone any essential 

 change of condition through the whole of the Tertiary period. 

 This conclusion I unhesitatingly indorsed; and though the an- 

 nouncement of it rather startled some of our geological Nestors, 

 it has come to be generally accepted by the younger generation 

 as by no means improbable. Subsequent reflection upon the 

 disproportion to which I have just referred, though from imperfect 

 data I at first z^^/^ffr-estimated it, disposed me to extend the ?ame 

 view to the ocean basins generally ; and happening at the same 

 time to become acquainted with the doctrines which had been 

 advanced by Professor Dana (then little known in this country), 

 I was strongly impressed by their accordance — this being the 

 more remarkable on account of the entire difference of the data 

 and lines of reasoning which led Professor Dana and myself to 

 the same conclusion.* 



We are now able to form an estimate of the relative masses of 

 Land and Sea which is probably not far from the truth. The 

 area of the existing land is to that of the sea as about i to 2f , or 

 as 4 : ii; so that if the entire surface of the globe were divided 

 into fifteen equal parts, the land would occupy only four of these, 

 or rather more than a quarter, whilst the sea would cover eleven, 

 or rather less than three-quarters. But the average height of 

 the whole land of the globe above the sea-level certainly does 

 not exceed looo feet, that of Asia and Africa being some- 

 what above that amount, while that of America (North and 

 South), Europe, and Australia is considerably below it. On the 

 other hand, the average depth of the ocean-floors is now known to 

 be at least 2\ miles, and may be taken (for the convenience of 

 round number) at 13,000 feet. Thus the average depth of 

 the ocean being 13 times as much as the average height of the 



* See my article "Atlantic," in the ninth edition of the Encyclopadia 



Bntannica. 



