206 THE BERMUDA ISLANDS. 



fathoms depth. There are probably few geologists who will 

 permit such a long period for the formation of this accessory 

 structure in a coral-reef. And if the lagoon itself is so ancient, 

 how old must be the structure in which it is implanted ? I 

 have discussed this subject on pp. 57-59, and have, I believed, 

 demonstrated that according to the determinations of the 

 quantity of organic and inorganic lime-sediment contained in 

 sea-water it would require a period of 100,000 years to build 

 up the thickness of a single foot from the oceanic abyss. In 

 shallow water, on the contrary, the process of construction may 

 be a very rapid one. 



H. B. Guppy. " Coral Formations." Nature, Mch. 15, 1888. 



The author defines the conditions governing the form and 

 the life of reefs as follows : " On the outer side of a reef we 

 have the directing influence of the currents, the increased food- 

 supply, the action of the breakers, etc. In the interior of a 

 reef we have the repressive influence of sand and sediment, 

 the boring of the numerous organisms that find a home on 

 each coral block, the solvent agency of the carbonic-acid in 

 the sea-water, and the tidal scour. These are all real agencies, 

 and we only differ as to the relative importance we attach to 

 each." No new facts bearing on these points are given. 



G. C. Bourne. " The Atoll of Diego Garcia and the Coral Formations of the Indian 

 Ocean." Nature, April 5, 1 888. 



A description of the southernmost atoll of the Chagos Group, 

 with considerations bearing on the structure of the other reefs 

 and coral islands of the Indian Ocean. The main facts con- 

 tained in this paper, as well as those contained in the more 

 elaborate article published by the same author in the Proc. 

 Royal Soc., XLIII, 1888, are discussed in the body of this 

 work. Mr. Bourne finds evidence of an elevation of some 4 

 feet in the Diego Garcia reef, and hence concludes that the 

 fact precludes "the idea of any subsidence being in progress, 

 as Mr. Darwin fancied to be the case in the Keeling atoll." 

 The raised atolls " atolls whose dry land just rises above the 

 waves and submerged banks " of the coral formations north 



