MUSEUM OF COMPARATIVE ZOOLOGY. 163 



if raised fourteen feet, would become a true atoll. According to Guppy/ 

 elevation is necessary to form an atoll and bring it within the destruc- 

 tive range of the sea, and a fringing reef, according to him, could not 

 be formed near shore or grow outwards. No such elevating action exists 

 along the whole line of the Florida Keys, yet the reef has grown up to 

 the action of the breakers. The same is the case with Kaneohe Bay. 



Neither fringing reefs, nor barrier reefs, nor atolls, grow exclusively 

 outward. I am inclined to consider the islets on the inner side of a 

 lagoon as remnants of islands formed by coral heads and coral sand 

 flats, rather than to suppose that the intervening channel has been eaten 

 away solely by the solvent action of sea-water. Leconte, as I have 

 stated, ascribes the limitation of corals towards the shore, and their 

 growth seaward, on the one hand to the muddiness of the inner waters 

 of the lagoon, and on the other to the purity of the water due to its 

 depth. It really seems doubtful whether the islands in the lagoon chan- 

 nel at Tahiti, mentioned by Murray,^ are portions of the original reef 

 still left standing, and not, as is the case with the coral heads in the 

 ship channel of the Florida Reef, independent coral patches, which have 

 not been overwhelmed by the action of sediment from the outer reef, 

 or as in the Tortugas, where we find active coral growth in the inner 

 Ime of the open channels. He further says, when coral reefs are much 

 broken up the coi-al growths in the lagoon are relatively abundant, while 

 there are but few coral patches and heads in the lagoons and lagoon 

 channels when the reefs rise to the surHice, or are nearly continuous. 

 This ie certainly the case at Kaneohe Bay. 



Geikie * also calls attention, in the examination of maps of coral 

 regions, to the difficulty of the theory of subsidence, as in the case of 

 the Fiji Islands, where fringing and barrier reefs and atolls all occur in 

 close proximity, and where all evidence seems to point to elevation, or at 

 least to a long period of rest. 



The fringing reef of Kaneohe Bay forms a scalloped outline, with an 

 occasional white coral sand beach where the wind has a wider sweep 

 than in the eastern and more protected parts of the bay. But these 



1 Guppy, H. B., Notes on the Characters and Mode of Formation of the Coral 

 Reefs of the Solomon Islands, being the Results of Observations made in 1882-84, 

 dunng the Surveying Cruise of H. M. S. Lark. Proc= Royal Soc. Edinb., 1885-86, 

 p. 857. 



2 Murray, Proc. Royal Soc. Edinb., 1879-80, p. 515, April 5, 1880, Vol. X. 

 No. 107. 



3 Geikie, The Origin of Coral Reefs. An Address read before the Royal Phys- 

 ical Society of Edmburgh. Proceedings, Vol. VIII. p. 1, 1884. 



