CORAL-REEFS. 179 



have been immense which at some period have been 

 upraised : in South America we may feel sure, and on the 

 north-western shores of the Indian Ocean we may suspect, 

 that this rising is either now actually in progress, or has 

 taken place quite recently. By our theory, we may con- 

 clude that the areas are likewise immense which have lately 

 subsided, or, judging from the earthquakes occasionally felt 

 and from other appearances, are now subsiding. The 

 smallness of the scale of our map should not be over- 

 looked : each of the squares on it contains (not allowing 

 for the curvature of the earth) 810,000 square miles. Look 

 at the space of ocean from near the southern end of the 

 Low Archipelago to the northern end of the Marshall 

 Archipelago, — a length of 4,500 miles, in which, as far as is 

 known, every island, except Aurora, which lies just without 

 the Low Archipelago, is atoll-formed. The eastern and 

 western boundaries of our map are continents, and they are 

 rising areas : the central spaces of the great Indian and 

 Pacific Oceans, are mostly subsiding ; between them, north 

 of Australia, lies the most broken land on the globe, and 

 there the rising parts are surrounded and penetrated by 

 areas of subsidence, 1 so that the prevailing movements now 

 in progress, seem to accord with the actual states of surface 

 of the great divisions of the world. 



The blue spaces on the map are nearly all elongated ; but 

 it does not necessarily follow from this (a caution, for which 

 I am indebted to Mr. Lyell), that the areas of subsidence 

 were likewise elongated; for the subsidence of a long, 

 narrow space of the bed of the ocean, including in it a 



1 I suspect that the Arru and Timor-laut Islands present an included 

 small area of subsidence, like that of the China Sea ; but I have not 

 ventured to colour them from my imperfect information, as given in the 

 Appendix. 



