32 STUDIES, SCIENTIFIC AND SOCIAL chap. 



is 2,250 feet, ^vhile the mean depth of all the oceans and 

 seas is 12,456 feet. In this estimate, however, all the in- 

 land seas and shallow coast waters are included, and as 

 these, at least as far as the 100-fathom line, are univer- 

 sally admitted to be within the " continental area," we 

 omit them in our estimate of the mean depth of the 

 oceans proper, which are thus brought to something over 

 15,000 feet, or nearly seven times as much as the mean 

 height of the land. 



The accompanying diagram (taken from my book on 

 Danvinism) will better enable the reader to appreciate 

 these proportions, which are of vital importance in the 

 problem under discussion. The lengths of the two parts 

 of the diagram are in proportion to the areas of land and 



Diagram of proportionate mean lieight of Land and depth of Oceans. 



Ocean 

 Area. -72 of area of Globe. 



Fig. 8. 



ocean respectively, the vertical dimensions, although for 

 distinctness on a greatly exaggerated scale, showing the 

 coiwpaTativG mean height and depth with sufficient accuracy. 

 It follows that the areas of the two shaded portions are 

 proportional to the bulk of the continents and oceans 

 respectively. 



The mean depths of the several oceans and the mean 

 heights of the several continents do not differ enough from 

 each other to render this diagram a very inaccurate repre- 

 sentation of the proportion between any of the continents 

 and their adjacent oceans ; and it will therefore serve, 

 roughly, to keep before the mind what must have taken 

 place if oceanic and continental areas had ever changed 

 places. It will, I presume, be admitted that, on any large 



