CORAL-REEFS. 121 



reef-building polypifers can exist, and it be assumed that 

 they can flourish at a depth of even 100 fathoms, yet the 

 weight of the above argument is but little diminished, for 

 it is almost equally improbable, that as many submarine 

 mountains, as there are low islands in the several great and 

 widely separated areas above specified, should all rise 

 within 600 feet of the surface of the sea and not one 

 above it, as that they should be of the same height within 

 the smaller limit of one or two hundred feet. So highly 

 improbable is this supposition, that we are compelled to 

 believe, that the bases of the many atolls did never at any 

 one period all lie submerged within the depth of a few 

 fathoms beneath the surface, but that they were brought 

 into the requisite position or level, some at one period and 

 some at another, through movements in the earth's crust. 

 But this could not have been effected by elevation, for the 

 belief that points so numerous and so widely separated 

 were successively uplifted to a certain level, but that not 

 one point was raised above that level, is quite as improbable 

 as the former supposition, and indeed differs little from it. 

 It will probably occur to those who have read Ehrenberg's 

 account of the Reefs of the Red Sea, that many points in 

 these great areas may have been elevated, but that as soon 

 as raised, the protuberant parts were cut off by the destroy- 

 ing action of the waves : a moment's reflection, however, 

 on the bason-like form of the atolls, will show that this is 

 impossible ; for the upheaval and subsequent abrasion of an 

 island would leave a flat disc, which might become coated 

 with coral, but not a deeply concave surface ; moreover, we 

 should expect to see, in some parts at least, the rock of the 

 foundation brought to the surface. If, then, the founda- 

 tions of the many atolls were not uplifted into the requisite 

 position, they must of necessity have subsided into it ; and 



