3fr Darwin on Coral Reefs. 49 



reefs, and tbercforo to the protection afforded by tliem. I can conceive 

 it vcr3' possible, that should, at some period, as far in futurity as the 

 secondary rocks are in the past, the bed of the Pacific, witli its atolls and 

 barrier reefs, be raised in reefs, b}' an elevation of some thousand feet, and 

 be converted into a continent, that scarcely any, or none of the existing 

 reefs would be preserved ; but only widely spread beds of calcareous 

 matter derived from their wear and tear. As a corollary from this, I sus- 

 pect that the reefs of the secondary periods (if any, as is probable, existed), 

 have been ground into sand, and no longer exist. This notion will cer- 

 tainly at first appear preposterous ; its only justification lies in the proba- 

 bility of upward movements after long periods of subsidence, being exceed- 

 ingl}' slow and often interrupted by pauses of rest, and perhaps of oscilla- 

 tions of land, during all which the soft coral rock would be exposed to the 

 action of waves never at rest. 



This notion, preposterous as it will probably appear, would not have 

 occurred to mc, had I not several times, from independent reasons, been 

 driven to the conclusion, that a formation to be preserved to a very dis- 

 tant a;ra (or which probably is the same thing, to be elevated to a great 

 height from its original level over a ivide area) must be of great extent, 

 and must be covered by a great thickness of superincumbent matter iu 

 order to escape the chances of denudation. I have come to this conclu- 

 sion chiefly from considering the character of the deposits of the long 

 series of formations piled one upon another, in Europe, with evidence 

 of land near many of them. I can explain my meaning more clearly 

 by looking to the future ; it scarcely seems probable, judging from 

 what I see of the ancient parts of the crust of the earth, tliat any of 

 the numerous sub-littoral formations {i. e. deposits formed along and 

 near shores, and not of great width or breadth), now accumulating on 

 most parts of the shores of Europe (and indeed of the whole world;, al- 

 though, no doubt, many of them must be of considerable thickness, will 

 be preserved to a period as far in the future, as the lias or chalk are in 

 the past, but that only those deposits of the present day will be preserved 

 which are accumulating over a wide area, and which shall hereafter chance 

 to be protected by successive thick deposits. I should think that most of the 

 sublittoral deposits of the present day will suffer, what I conclude the 

 sublittoral formations of the secondary reras have generally suffered, 

 namely, denudation. Now, barrier and atoll coral reefs, though, accord- 

 ing to my theory, of great thickness, are, in the above sense, not widely 

 extended j and hence I conclude they will suffer, as I suspect ancient 

 coral rccCs have suffered — the same fate with sublittoral deposits. 



With respect to the vertical amount of subsidence, requisite by my 

 threory to have produced the spaces coloured blue on the map, more facts 

 regarding the average heights of islands and tracts of land are wanted 

 than all those, even if perfectly known, which this one world of ours 

 would afford ; for the question of the probable amount, or, which is the 

 same thing, the probable tliickncss of the coral-reef, resolves itself into 

 this, — AVlint is the ordin;iry luight of tracts of land, or groups of islands 



VOL. XXXIV. XO. LXVII. JANUARY 1843. 1) 



