126 CRITIQUES AND ADDRESSES. [vi. 



accumulation, at the foot of its seaward face, of a talus 

 of coral fragments torn off by the violence of the waves, 

 which talus might, in course of time, become high 

 enough to bring its upper surface within the limits of 

 coral growth, and in that manner provide a sort of 

 factitious sea-bottom upon which the coral embryos 

 might perch. If, on the other hand, the level of the 

 sea were slowly and gradually lowered, it is clear that 

 the parts of its bottom, originally beyond the limit of 

 coral growth, would gradually be brought within the 

 required distance of the surface, and thus the reef might 

 be indefinitely extended. But this process would give 

 rise neither to an encircling reef nor to an atoll, but to a 

 broad belt of upheaved coral rock, increasing the dimen- 

 sions of the dry land, and continuous seawards with the 

 fresh frin <nn reef. 



o o 



Suppose, however, that the sea-level rose instead of 

 falling, at the same slow and gradual rate at which we 

 know it to be rising in some parts of the world not 

 more, in fact, than a few inches, or, at most, a foot or 

 two, in a hundred years, Then, while the reef would be 

 unable to extend itself seaward, the sea-bottom outside 

 it being gradually more and more removed from the 

 depth at which the life of the coral polypes is possible, 

 it would be able to grow upwards as fast as the sea rose. 

 But the growth would take place almost exclusively 

 around the circumference of the reef, this being the only 

 region in which the coral polypes would find the con- 

 ditions favourable for their existence. The bottom of 

 the lagoon would be raised, in the main, only by the 

 coral debris and coral mud, formed in the manner 

 already described ; consequently, the margins of the reef 

 would rise faster than the bottom, or, in other words, 

 the lagoon would constantly become deeper And, at 

 the same time, it would gradually increase in breadth ; 



