COEAL STRUCTURES. 91 



mfr reefs, encircling or barrier reefs, and atolls or ring 

 reefs, is that propounded and ably maintained by Darwin, 

 that the whole area of the Pacific is slowly sinking; that 

 all the reefs and islands are the summits of former moun- 

 tains ; that all the coral structures were originally attached 

 to the land at a shallow depth, and that, to whatever depth 

 below they now extend, it is only in a dead condition, 

 and has been effected by the subsidence of the supporting 

 land carrpng the coral with it ; while the successive gene- 

 rations of the living polypes, ever working upwards on the 

 old dead foundation, have maintained a living coral struc- 

 ture near the surface, and that nearly in the same outline 

 and form as the orio-inal foundation. 



It does not accord with my purpose to enter into the 

 details of this beautiful theory, but rather to present my 

 readers with some vivid pictures of the wonderful struc- 

 tures themselves, as sketched by those who have seen 

 them. In coasting along a trojDical reef, the extreme 

 clearness of the water permits the coral shrubs and groves 

 to be distinctly seen, which rise from the blue transparent 

 depths. They take various forms — some massive, with 

 meandering channels over the rounded surface ; some 

 forming honey-combed blocks formed by the union of 

 thin plates at various angles ; many growing like trees or 

 shrubs with leafless branches, more or less ramified, and 

 with the twigs more or less slender and pointed, or thick 

 and rounded. Under water, the whole surface is covered 

 with a layer of jelly-like flesh, of many brilliant colours, 

 formed by the crowding together of the myriad tiny 

 polypes, which protrude their slender tentacles and ex- 



