THEIR RELATION TO VOLCANOES. 279 



Authors have noticed with surprise that although 

 atolls are the commonest coral-structures through- 

 out some enormous oceanic tracts, they are entire- 

 ly 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 ai-eas, coloured red and blue, are all elon- 

 gated ; and between the two colours there is a de- 

 gree 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 in- 

 stance, in South America) where there are no 

 reefs, we are led to conclude that the great conti- 

 nents 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 volcanoes 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 are led to con- 

 clude, 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 hun- 

 dred miles of an archipelago, or even small groups 



