152 THEORY OF THE FORMATION Ch. V. 



It has, I think, been shown in this chapter, that 

 subsidence explains both the normal structure and 

 the less regular forms of those two great classes of 

 reefs which have justly excited the astonishment of all 

 the naturalists who have sailed through the Pacific and 

 Indian Oceans. The necessity, also, that a foundation 

 should have existed at the proper depth for the growth 

 of the corals over certain large areas, almost compels 

 us to accept this theory. But further to test its truth, 

 a crowd of questions may be asked. Do the different 

 kinds of reefs which have been produced by the 

 same kind of movement, generally lie within the 

 same or closely adjoining areas ? How are such reefs 

 related to each other in form and position, — for 

 instance, do neighbouring groups of atolls, and the 

 separate atolls in each group, bear the same relation 

 to each other as do ordinary islands ? Although coral- 

 reefs which have just begun to re-grow, after having 

 been killed by too rapid a subsidence, would at first 

 belong to the fringing class, yet, as a general rule, 

 reefs of this class indicate that the land has either 

 long remained at a stationary level, or has been up- 

 raised. Of a stationary level it is hardly possible 

 to find any evidence except of a negative kind ; but 

 of recent elevation, upraised marine remains afford a 

 sure proof: it may therefore be asked, do fringed 

 coasts often afford such evidence? Do the areas 

 which have subsided, as shown by the presence of 

 atolls and barrier-reefs, and the areas which have 

 either remained stationary or have been upraised, 



