3$d 1)l$TRIBLtlON OF CORAL-REEFS. [CHAR x>. 



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 ef 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 that they 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 movement. 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 

 existing 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 seas, as in the West Indies : we can 

 now at once perceive the cause, for where there has not been subsidence, 

 atolls cannot have been formed ; and in the case of the West Indies 

 and parts of the East Indies, these tracts are known to have been rising 

 within the recent period. The larger areas, coloured red and blue, are 

 all elongated ; and between the two colours there is a degree of rude 

 alternation, as if the rising of one had balanced the sinking of the other. 

 Taking into consideration the proofs of recent elevation both on the 

 fringed coasts and on some others (for instance, in South America) 

 where there are no reefs, we are led to conclude that the great con- 

 tinents are for the most part rising areas ; and from the nature of the 

 coral-reefs, that the central parts of the great oceans are sinking aceas. 

 The East Indian Archipelago, the most broken land in the world, is 

 in most parts an area of elevation, but surrounded and penetrated, 

 probably in more lines than one, by narrow areas of subsidence, i 



I have marked with vermilion spots all the many known active 

 volcanos within the limits of this same map. Their entire absence 

 from every one of the great subsiding areas, coloured either pale or 

 dark blue, is most striking ; and not less so is the coincidence of tlie 

 chief volcanic chains with the parts coloured red, which we are led to 

 conclude have either long remained stationary, or more generally have 

 been recently upraised. Although a few of the vermilion spots occur 

 within no great distance of single circles tinted blue, yet not one single 

 active volcano is situated within several hundred miles of an archipelago, 

 or even small group of atolls. It is, therefore, a striking fact that in 

 the Friendly Archipelago, which consists of a group of atolls upheaved 

 and since partially worn down, two volcanos, and perhaps more, are 

 historically known to have been in action. On the other hand, although 

 most of the islands in the Pacific which are encircled by barrier- reefs, 

 are of volcanic origin, often with the remnants of craters still distin- 

 guishable, not one of them is known to have ever been in eruption. 



