304: A. Agassiz — Expedition to the Maldives. 



* 

 above the surface. The shape of these rings or bars or flats is 

 not necessarily circular, it varies greatly and is indirectly con- 

 trolled by the topography of the bottom. Some of these faros 

 are elliptical, pear-shaped, or crescent-shaped, varying greatly in 

 outline and dimensions on the outer lines of the composite 

 atolls. In some of the atolls the lagoons of the smaller atolls 

 have been formed by the growth of coral patches or lines of 

 corals rising at a short distance lagoonward, parallel with the 

 outer reef fiat. These patches become joined and form thus 

 elongated lagoons or a number of secondary lagoons on the 

 outer reef flats. 



There is no evidence that these small atolls are the result of 

 the splitting or breaking up of what was formerly a larger atoll, 

 nor that adjoining atolls or reef flats have become united or 

 coalesced except where the passages separating them have been 

 of very moderate depths. No such changes are indicated any- 

 where from a comparison of the conditions as marked on the 

 chart of 70 years ago and those existing to-day. 



The outer slopes of these rings are covered with corals grow- 

 ing with great luxuriance from the edge or even far on the 

 flats of the ring to a depth of from eight to twelve or fifteen 

 fathoms. The superb growth of corals found in all the so-called 

 lagoons of the Maldives is in marked contrast with the scanty 

 growth of corals in the lagoons of the atolls of the Pacific. 

 It seems we have a simple explanation of this in the fact that 

 the rim of these so-called atolls in the Maldives is full of wide 

 and deep passages. In fact, the extent of the passes is generally 

 much larger than the space occupied by the small atolls (the 

 atollons). As soon as the flats of the rings have reached the 

 surface, either wholly or in part, sand bars begin to form, and 

 these develop rapidly into islets and finally large islands more 

 or less covered with scrub vegetation and bushes. These rings 

 or faros either retain a central lagoon or it becomes partly or 

 wholly filled up. In the former case they appear as small atolls 

 with islands or islets on the reef flats ; in the next stage there is 

 only a smaller lagoon on the lee face of a larger island, or else 

 the island has grown to occupy the whole flat of the faro with 

 only very narrow flats on the lagoons faces of which corals 

 grow. These larger islands are often covered with fine vegeta- 

 tion, large trees occupying the space inside of the outer belt of 

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

 many islands which dot the so-called lagoons of the Maldives 

 have been formed in the manner described, and it is compara- 

 tively easy to trace the progress of development in all the 

 stages intermediate between a mere ring not yet rising to the 

 surface and an island with its rich vegetation such as we find 

 either in the lagoons or on the outer edge of the Maldivian 

 composite atoll. 



