How Animals Work. 



then, is the substratum, and how was it formed ? If 

 composed of a coral rock, then it is clear that it must 

 have been formed at a time when it was nearer to the 

 surface of the sea than it is now, and that it must later 

 on have subsided to greater depths. If, however, this 

 substratum is a primitive rock, then it would appear 

 that in such regions as the Indian and South Pacific 

 Oceans, where archipelagoes and atolls extend for 

 hundreds of miles, there must exist submerged chains 

 of mountain ranges whose peaks reach to a uniform 

 level beneath the surface of the sea. This is highly 

 improbable, for, as Charles Darwin states in his Coral 

 Reefs, " we cannot believe that a broad mountain summit 

 lies buried at a depth of a few fathoms beneath every 

 atoll, and nevertheless that throughout the immense 

 areas above named not one point of rock projects above 

 the level of the sea. For we may judge of mountains 

 beneath the sea by those on land, and where can we find 

 a single chain, much less several such chains many hun- 

 dred miles in length, and of considerable breadth, with 

 broad summits attaining the same height from within one 

 hundred and twenty to one hundred and eighty feet ? " 



To account for this, Darwin worked out his famous 

 subsidence theory, according to which the regions where 

 atolls now occur were once dry land, or an archipelago 

 of volcanic islands surrounded by fringing coral reefs. 

 We have the most convincing proof in almost all parts 

 of the world that land has disappeared beneath the 

 surface of the sea, only to reappear again at a later 

 epoch in the earth's history. Thus Darwin, as in all 

 his work, was building his theory upon a solid founda- 

 tion of ascertained fact. In the regions, therefore, where 



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