MUSEUM OF COMPARATIVE ZOOLOGY. 161 



the isolated patches in the bay, we find mainly Pocilloporae, and shel- 

 tered by them in the interior circle of the coral patches solitary Fungire 

 with a few Gorgonise, which seem to be much less numerous than upon 

 the reef near Honolulu, and there are also comparatively few algae and 

 corallines. The large masses of Pontes growing near the shore have 

 little by little been choked by the silt coming down from the Pali, and 

 a volcanic sand flat, with a band of living corals on the outer edge, is 

 thus formed near the fringing reef, in marked contrast to the coral sand 

 flats formed by the action of the breakers. 



The whole bay before corals began to flourish upon it must have 

 contained a number of small volcanic islands, and a large number of 

 sunken volcanic rocks and ledges, which have become capped with coral 

 or surrounded by diminutive fringing reefs. What is now going on in 

 the Bay of Kaneohe on a diminutive scale, we may apply to groups of 

 volcanic islands in the Pacific. If we add to this the powerful agency 

 of accumulations of limestone on the deeper summits or banks, until 

 these surfaces are built up to a height at which corals can begin to grow, 

 we have all the various elements needed for the formation of fringing 

 reefs, barrier reefs, or atolls within a comparatively limited area, as is 

 the case in those archipelagoes of the Pacific where these various kinds 

 of reefs have been observed to occur together. The base upon which 

 the barrier reef of Kaneohe has been built up has probably been formed 

 by the washing down and disintegrating of a lava crest of considerable 

 height, if we may judge of it from Mokolii. 



According to Dana and Darwin the line of barrier reefs and of atolls 

 indicates the former extent of the area of land before the reefs began to 

 form, which in some cases was three or four times that now above the 

 level of the sea, and in the whole Pacific reef district the atolls and reefs 

 are the monuments of islands which have long ceased to exist. 



The formation of a barrier reef upon a foundation denuded to the 

 depth at which corals can flourish has not been observed before. Cap- 

 tain Wharton x gives a very interesting account of " the preparation of a 

 suitable foundation for coral builders by a process directly the reverse of 

 that of building up by marine organisms on mounds that have failed to 

 reach the surface," from which it appears probable " that the cinders 

 and ashes which formed, and still form, the summit of the volcanic 

 mound originally thrown up, are being by wave action gradually swept 

 away, and will continue to be so removed until the top of the bank is 

 reduced below the limit of such action, or the solid rock is laid bare." 



1 W. J. L. Wharton, "Foundation of Coral Reefs," Nature, October 11, 1888. 

 VOL. xvii. — no. 3. 11 



