Ch. VI. DISTRIBUTION OF CORAL-REEFS. 187 



appended map, it may, I think, be considered as 

 almost established, that volcanos are often present in 

 the areas which have lately risen or are still rising, 

 and are invariably absent in those which have lately 

 subsided or are still subsiding ; and this, I think, is 

 the most important generalisation to which the study 

 of coral-reefs has indirectly led me. 1 



On the dimensions and relative positions of the 

 subsiding areas on our map, as indicated by the pre- 

 sence of atolls and barrier-reefs ; and of the rising or 

 stationary areas, as knoivn by upraised organic re- 

 mains, or inferred from the presence of f ringing-reefs. 

 — The immense surfaces seen on the map, which ac- 

 cording to our theory, or from the plain evidence of 

 upraised remains, have undergone either a downwards 

 or upwards change of level within a geologically late 

 period, is a highly remarkable fact. The existence of 

 continents shows that the areas which have been up- 

 raised are immense. With respect to South America 

 we may feel sure, and with respect to the western shores 

 of the Indian Ocean we have reason to suspect, that 

 this rising is either now actually in progress, or has 

 taken place quite recently. By our theory, it may 

 safely be inferred that the areas which have lately sub- 

 sided are likewise immense ; or, judging from the earth- 

 quakes now occasionally felt there, and from other ap- 



1 We may infer from this rule, that at any place where an old formation 

 contains interstratified beds of erupted matter, the surface of the land 

 or the bed of the sea, formed, at the period of eruption, a rising, at 

 least not a subsiding area. 



