INTRODUCTION. xvii 



lagoon faces of which corals grow. The larger islands are often covered 

 with fine vegetation, large trees occupying the space bordered by the outer 

 belt of bushes growing close to the beach. The greater number of the 

 many islands which dot the large lagoons of the Maldives have been formed 

 in the manner described, and it is comparatively easy to trace the progress 

 of their development in all the stages intermediate between a mere ring, 

 not yet rising to the surface, and a steep to island with its rich vegetation 

 such as we find either in the lagoons or on the outer edge of a Maldivian 

 composite atoll. 



The small atolls which form the outer rim of the composite atolls owe 

 their existence to the same causes, and their development can be as easily 

 traced from a mere ring which has risen to the surface having more or less 

 extensive flats on which islands or islets or sand-bars have been thrown up. 

 The sea reef flats of the outer lines of atolls are usually wider than those 

 of the lee face, and naturally so. 



From my observations I am inclined to look upon Nullipores much as 

 does Mr. Gardiner, 1 as especially efficient in consolidating the corals and in 

 the protection of reef platforms and flats. Nullipores also flourish on the 

 sea faces of coral reefs to the greatest depths at which corals grow, but 

 they are far more important below that depth in lagoons. 



As far as I have examined the outer slopes of the reef flats or faros 

 of the various banks, they are covered with a growth of corals down to a 

 depth of twenty to twenty-one fathoms, taking their greatest development 

 at from five to nine or ten fathoms and rapidly disappearing from seven- 

 teen to twenty-five fathoms, where the coral slope passes into a region 

 barren of reef corals. 



Mr. Gardiner comes to the conclusion that about thirty fathoms is the 

 extreme limit of the growth of the effective reef-building corals. He also 

 noticed, what is generally the case in the Pacific, that, modified by local 

 conditions, corals grow more luxuriantly as the water becomes shallower 

 to within three to six fathoms of the surface. From his observations 2 

 Gardiner concludes Darwin is correct in stating that the extreme depth 

 of reef corals is not more than twenty-five fathoms. There are great diffi- 



1 Loc. cit., p. 177. a Loc. cit., p 325. 



