1836.] AREAS OF SUBSIDENCE AND ELEVATION. 461 



sidence 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, coloitred 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 considera- 

 tion 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 continents 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 areas. 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 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 

 the chief volcanic chains with the parts coloured red, which we arc 

 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 archi- 

 pelago, which consists of a group of atolls upheaved and since 

 partially worn down, two volcanos, and perhaps more, are histori- 

 cally 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 

 distinguishable, not one of them is known to have ever been in 

 eruption. Hence in these cases it would appear, that volcanos 

 burst forth into action and become extinguished on the same spots, 

 accordingly as elevatory or subsiding movements prevail there. 



