reefs, was able to establish conclusively that it is, in 

 fact, a form of animal life. Once this fact was accepted, 

 scientists who followed the early navigators to the tropi- 

 cal seas began to take a great interest in the manner 

 whereby such creatures were able to build atolls, barrier 

 reefs and fringing reefs. The great difficulty v/as to 

 explain the appearance of atolls in the middle of deep 

 oceans. At one time it was thought that corals grew at 

 the bottoms of the deep tropical seas, and that succeed- 

 ing generations of them, growing upon the accumulated 

 dead limestone skeletons of their ancestors, would in 

 the course of millions of years reach the surface. Such 

 ideas however, were soon dispelled by the dredging 

 operations carried out by naturalists, whereby specimens 

 of sea life are dragged up from the bottom. The result 

 of these early studies showed quite clearly that reef 

 corals are unable to grow except in relatively shallow 

 water. Darwin, in his celebrated book, 'The Struc- 

 ture and Distribution of Coral Reefs,'' made it plain 

 that reef corals grow vigorously in water less than 1 00 

 feet deep and that they are unable to live at all below 

 about 1 50 feet. Thus any theory of the origin of coral 

 reefs must, first of all, account for the existence of a 

 platform upon which the coral may grow, situated at a 

 distance below the surface of less than about 1 50 feet. 

 The reasons for the inability of corals to grow below this 

 depth are briefly discussed in Section 1 of this hand- 

 book. 



It will be seen immediately that no particular prob- 

 lem attaches to fringing reefs, since these are always 

 close to land, which acts as a suitable platform where 

 it extends below the surface. In order to account for 

 barrier reefs, up to 100 miles from land, or for atolls, 



27 



