Ch. VI. DISTRIBUTION OF CORAL-REEES. 185 



the active volcanic vents in relation to neighbouring- 

 islands and coasts, situated at too great a distance for 

 any corals growing there to be injured by the eruptions ; 

 and where, from the presence of atoll-formed or barrier- 

 reefs, or of upraised marine remains, we have reason 

 to believe that either subsidence or elevation has 

 occurred within a recent period. 



The following cases offer a few partial exceptions to 

 the rule that active volcanos are situated at a distance 

 from the areas of subsidence. The Great Comoro 

 Island probably contains a volcano, and it is only 

 twenty miles distant from the barrier-reef of Mohila. 

 Ambil volcano, in the Phillippine Archipelago, is dis- 

 tant only a little more than sixty miles from the atoll- 

 formed Appoo reef : and there are two other volcanos 

 on the map within ninety miles of circles coloured 

 blue. But there is not a single active volcano within 

 several hundred miles of a group, even a small group, of 

 atolls ; and it is clear that a group of atolls, surmount- 

 ing a number of islands now all sunk beneath the level 

 of the sea, implies a much greater amount of subsi- 

 dence, than does a single atoll or a single encircling* 

 barrier-reef. It is a striking fact that Wo volcanos are 

 known to have been in recent action in the Friendly 

 Archipelago ; and the islands have here been formed 

 by the recent elevation of a group of atolls. Again, 

 extinct craters and well-preserved streams of lava occur 

 on many of the encircled islands in the Pacific, and 

 these by our theory have subsided at no very remote 

 period ; but although thus plainly formed of volcanic 



