President's Address. 29 



reefs and atolls are in vigorous growth. Such an associa- 

 tion of upheaval with an assumed general subsidence requires, 

 on the subsidence theory, a cumbrous and entirely hypo- 

 thetical series of upward and downward movements. These 

 are unnecessary, if we can be convinced that coral-reefs grow 

 up independent of terrestrial movements, which may, in one 

 area, be in an upward, in another, in a downward, direction. 

 From this point of view, the reefs stand up as the result of a 

 complex series of agencies, among which the more important 

 are, on the one hand, the temperature, solvent power, currents, 

 tides, and waves of the sea ; and, on the other hand, the 

 amount and direction of the supply of pelagic food, the up- 

 building of calcareous deposits to the zone of reef-builders, 

 the vigorous growth of the coral masses on their outer faces, 

 and their death, decay, and the solution of their skeletons in 

 the inner parts of the reefs. All these causes are known and 

 visibly active. Without the co-operation of any other sup- 

 posed or latent force, they appear to be entirely adequate to 

 the task of building up the present coral-reefs of the oceans. 

 I fear I have considerably overstepped the limits of time 

 within which this address should have been confined. Let 

 me only, in conclusion, advert to the interesting bearing of 

 our newer information about coral-reefs and modern marine 

 limestones upon the elucidation of the origin of ancient lime- 

 stones. Every geologist who has worked among the calcare- 

 ous intercalations of the older palaeozoic rocks, is familiar 

 with their frequent strangely lenticular character. A lime- 

 stone, several hundred feet thick, suddenly dwindles down 

 and disappears in a most inexplicable way. The suggestion 

 of cross-faults cannot be entertained. If, however, we regard 

 such limestones as akin in their mode of growth to modern 

 coral-reefs, whether formed by actual corals or by other reef- 

 builders, we obtain a possible solution of the difficulty. A 

 very successful attempt in this direction has recently been 

 made by my friend M. Dupont, Director of the Geological 

 Survey of Belgium, in reference to the remarkable lenticular 

 masses of limestone in the Devonian system of Belgium.^ 



^ Bulletin Acad. Royale Belgique, 3d ser., tome ii., 1881, p. 264; Bulletin 

 Mus. Royal Belgique, 1883. 



