616 



DYNAMICAL GEOLOGY. 



wooded side is that to the windward, unless it happens to be under 

 the lee of another island. On the leeward side there are often chan- 



Fig. 849. 



Fis. 850. 



Atolls.— Fig. 849, Apia, one of the Kingsmill Islands; 850, Menchikoff, one of the 

 Carolines. 



nels opening through to the lagoon (e, fig. 849), which, when deep 

 enough for shipping, make the atoll a harbor ; and some of these 

 coral-girt harbors in mid-ocean are large enough to hold all the 

 fleets of the world. 



Fig. 851 represents a section of an island, from the ocean (o) 

 to the lagoon {I). On the ocean. side, from o to a there is shallow 

 water for some distance out (it may be a quarter or half a mile or 

 more); and, where not too deep (not over one hundred feet), the 

 bottom is covered here and there with growing corals, a to b is a 

 platform of solid coral rock, mostly bare at low tide, but covered 



Fig. 851. 



Section of a coral island, from the ocean (o) to the lagoon (I). 



at high, and having a width usually of about a hundred yards : 

 there are shallow pools in many parts of it, abounding in living 

 corals of various hues, Actiniae (Sea-anemones), Star-fishes, Sponges, 

 Shells, Shrimps, and other kinds of tropical life, and towards 

 the outer margin it is quite cavernous, and the holes are fre- 

 quented by crabs, fishes, etc. At b is the. white beach, six or eight 

 feet high, made of coral sand or pebbles and worn shells ; b to d is 

 the wooded portion of the island. The whole width from the beach 

 (b) to the lagoon (c) is commonly not over three or four hundred 



