1904-1905-] Recent Views regarding Coral Reefs. 177 



after a time as a shelf or rocky ledge, which cannot well 

 extend very far seawards without some support beneath. 

 This support is furnished by the blocks of coral that are fre- 

 quently broken off by the heavy seas which pound and batter 

 the outer edge of the reef. This destructive work of the sea 

 is much facilitated by the fact that the reef is riddled through 

 and through in all directions by the tunnels driven by various 

 boring animals, which make their way into the solid substance 

 of the reef in order to obtain shelter from their numerous 

 enemies. So large blocks of coral are from time to time 

 broken off, and they fall on to the slopes beneath the edge of 

 the reef, where they help to form what one may term step- 

 ping-stones, upon which the growing corals gradually make 

 their way farther out to sea. 



The growth of a coral reef is only in part effected by 

 corals. Much coral sand is cast up by the waves into the 

 reef. The tiny shells of foraminifera accumulate there from 

 the same cause. Numerous lime-secreting animals of various 

 kinds live and die on a reef. All these contribute more or 

 less to the accumulation of carbonate of lime, and the solvent 

 action of surface-waters helps to reduce much of this matter 

 to a fluid state, in which it serves to bind the loose parts of 

 the reef into one hard compact mass, which may eventually 

 become even crystalline in texture, and as close-grained as 

 one of the limestones of the Carboniferous rocks. But the 

 chief agent concerned in this cementing and compacting pro- 

 cess, and therefore in the conservation of the reef, is that of 

 the Millepores. These are lime -secreting algae, belonging 

 chiefly to the Florideae, and they are represented mostly by 

 the algae of the genus Lithothamnion, Enormous quantities 

 of carbonate of lime are fixed upon each reef by the action of 

 these rock -forming plants. Indeed the Millepores may be 

 regarded as taking a part in the construction of the reef but 

 little inferior in importance to that played by the corals 

 themselves. 



The seaward growth of a reef tends, as time goes on, to 

 leave the earlier formed corals farther and still farther re- 

 moved from the source of food-supply. Hence these older 

 portions of the reef after a time come to consist of little else 



