1836.] DISTRIBUTION OF CORAL REEFS. 471 



through their normal changes, and through occasional 

 accidents of their existence, to their death and final 

 obliteration. 



In my volume on Coral Formations I have published a 

 map, in which I have coloured all the atolls dark blue, the 

 barrier-reefs pale blue, and the fringing-reefs red. These 

 latter reefs have been formed whilst the land has been 

 stationary, or, as appears from the frequent presence 01 

 upraised organic remains, whilst it has been slowly rising : 

 atolls and barrier-reefs, on the other hand, have grown up 

 during the directly opposite movement of subsidence, which 

 movement must have been very gradual, and in the case 

 of atolls so vast in amount as to have buried every 

 mountain-summit over wide ocean-spaces. Now in this 

 map we see that the reefs tinted pale and dark blue, 

 which have been produced by the same order of movement, 

 as a general rule manifestly stand near each other. Again 

 we see, that the areas with the two blue tints are of wide 

 extent ; and thatthey lie separate from extensive lines of coast 

 coloured red, both of which circumstances might naturally 

 have been inferred, on the theory of the nature of the reefs 

 having been governed by the nature of the earth's move- 

 ment. It deserves notice, that in more than one instance 

 where single red and blue circles approach near each other, 

 I can show that there have been oscillations of level ; for 

 in such cases the red or fringed circles consist of atolls, 

 originally by our theory formed during subsidence, but 

 subsequently upheaved ; and on the other hand, some of 

 the pale blue or encircled islands are composed of coral- 

 rock, which must have been uplifted to its present height 

 before that subsidence took place, during which the exist- 

 ing barrier-reefs grew upwards. 



Authors have noticed with surprise, that although atolls 

 are the commonest coral -structures throughout some 

 enormous oceanic tracts, they are entirely absent in other 

 sf-as, as in the West Indies : we can now at once perceive 

 ihe cause, for where there has not been subsidence, atolls 

 rannot have been formed ; and in the case of the West 

 Indies and parts of the East Indies, these tracts are known 



. have been rising within the recent period. The larger 



•as, coloured red and blue, are all elongated; and 

 i/'tween the two colours there is a dr-gree of rude alterna- 

 tion, as if the rising of one had balanced the sinking of the 



