CORALS. 525 



the better growth of the corals on the outer edges of the reef which are most 

 exposed to the action of the surf, and the sweeping of the coral material out of the 

 lagoon through the agency of oceanic currents, and the dissolving action of the 

 carbonic acid contained in the sea water. The deep canals which divide the 

 barrier-reefs from the neighbouring mainland are formed in the same way. The 

 enormous magnitude of the reefs which the theory of subsidence demands is 

 nowhere realised. Neither among modern reefs nor among geological formations 

 do we find any traces of such gigantic masses of coral-rock. We are thus in 

 face of a fascinating and important scientific problem, which still remains to 

 be solved, a problem which was long thought to have found its solution. After 

 Darwin's and Dana's subsidence theory had been generally for many years 

 accepted as beautiful and completely satisfactory, we are told that it is not 

 always applicable, and that much simpler causes suffice to explain the phenomena. 

 It is obvious, then, that we have an ample supply of possible explanations of 

 coral-reefs, and it is most probable that among the many scattered reefs in the 

 world, in one case one set of factors have played the chief part, in another case 

 a slightly different set, and further, a detailed and exhaustive study of any 

 particular reef would probably reveal natural processes of no small importance 

 which have not as yet been taken into account. 



H. AND M. BERNARD. 



MOUTHS OP MADREPORE. 



