n6 CORAL-REEFS. 



like the northern Maldiva atolls, made up of numerous 

 ring-formed reefs, placed on the margin of a disc, — one of 

 which discs is eighty-eight miles in length, and only from 

 ten to twenty in breadth. It is, also, not a little improbable 

 that there should have existed as many craters of immense 

 size crowded together beneath the sea, as there are now in 

 some parts atolls. But this theory lies under a greater 

 difficulty, as will be evident, when we consider on what 

 foundations the atolls of the larger archipelagoes rest : 

 nevertheless, if the rim of a crater afforded a basis at the 

 proper depth, I am far from denying that a reef like a 

 perfectly characterised atoll might not be formed ; some 

 such, perhaps, now exist ; but I cannot believe in the 

 possibility of the greater number having thus originated. 



An earlier and better theory was proposed by Chamisso; 1 

 he supposes that as the more massive kinds of corals prefer 

 the surf, the outer portions, in a reef rising from a sub- 

 marine basis, would first reach the surface and consequently 

 form a ring. But on this view it must be assumed, that in 

 every case the basis consists of a flat bank ; for if it were 

 conically formed, like a mountainous mass, we can see no 

 reason why the coral should spring up from the flanks, 

 instead of from the central and highest parts : considering 

 the number of the atolls in the Pacific and Indian Oceans, 

 this assumption is very improbable. As the lagoons of 

 atolls are sometimes even more than forty fathoms deep, it 

 must, also, be assumed on this view, that at a depth at 

 which the waves do not break, the coral grows more 

 vigorously on the edges of a bank than on its central part ; 

 and this is an assumption without any evidence in support 

 of it. I remarked, in the third chapter, that a reef, growing 



1 Kotzebue's First Voyage, vol. iii. p. 331. 



