Mr Darwin on Coral Reefs. 



49 



reefs, and therefore to the protection afforded by them I can conceive 

 t; possible, that should, at some period, as far in atunty as Il.e 

 econiu'' rocks are in the past, the bed of the Paeme, .v.th .ts atoll and 

 barrier re'efs, be raised in reefs, by an elevation of some thousand feet, and 

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

 reefs" ould be preserved; but only widely spread beds of calcareous 

 matter derivedfrom their wear and tear. As a corollary from thi., 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- 

 bilit3^of upward movements after long periods of subsidence being exceed- 

 ingly slow and often interrupted by pauses of rest, and perhaps of osc.lla- 

 tioVs 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 tome, had I not several times, from independent reasons, been 

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

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

 heioht from its original level over a wide area) must be of great extent, 

 and must be covered by a great thickness of superincumbent matterm 

 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 trora 

 what I see of the ancient parts of the crust of the earth, that any ot 

 the numerous sub-llttoral formations (t. 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- 

 thouoh, no doubt, many of them must be of considerable thickness, wdl 

 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 

 ^vhich are accumulating over a wide area, and which shall hereafter chanee 

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

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

 subllttoral formations of the secondary »ras have generally suffered, 

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

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

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

 coral reefs have suffered-the same fate with sublittoral deposits. 



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

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

 re<.arding 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, winch is the 

 .amc thing, the probable thickness of the coral-reef, resolves itself into 

 tl.is,— What is the ordinary height of tracts of land, or groups ot islands 

 VOL. XXXIY. XO. LXYII. JANUARY 1843. ^ 



