266 TOILERS IN THE SEA. 



of the growth, or extension of coral, either laterally 

 or vertically, in the formation of reefs, as considered 

 apart from the growth of individual species. On 

 this point all the evidence we can produce is that 

 collected by Darwin, and that of a very limited 

 character. It has been assumed that the vertical 

 growth of coral must be slow, as inferred from a few 

 instances often cited, but which Darwin declares 

 are inconclusive. Ehrenberg has said, for instance, 

 that in the Red Sea, corals only coat other rocks in 

 a layer from one to two feet in thickness, or at most 

 to nine feet, and he did not believe that in any case 

 they would, of their own proper growth, form stratified 

 masses. He alludes to certain large massive corals 

 in the Red Sea, which he imagined of such vast 

 antiquity as to have been cotemporaneous with 

 Pharoah. On this point Darwin admits that there 

 are reefs in the Red Sea which do not appear to 

 have increased in dimensions during half a century, 

 and from comparison of old charts, probably not 

 during the last two hundred years. These, and 

 similar facts, have strongly impressed many with 

 the belief of the extreme slowness of the growth of 

 corals, so that they have even doubted the possibility 

 of islands in the ocean being formed by this agency. 

 On the contrary, there are facts, from which it may 

 be inferred with certainty, that masses of considerable 

 thickness have been formed by the growth of coral. 



