162 BULLETIN OF THE 



Dana argues agaiust the possibility of coral reefs being planted upon 

 submarine banks of the requisite depths for corals to thrive, yet this is 

 actually what we see going on in Florida, and we can there trace all 

 the steps from the barrier reef to the keys, and to the incipient reef or 

 coral bank making a beginning upon the limestone bank which has been 

 raised by accretion to the depth requisite for the growth of corals. It 

 seems to me that a wide flat reef cannot be formed by a slow subsid- 

 ence, but must have gi'own, during a period of rest or slow elevation, 

 simply by the dying out of the coral next to the land, as has been ob- 

 served on the shore edge of Kaneohe Bay. 



Captain Wharton x has also given, in a recent number of "Nature," a 

 number of instances of the growth of corals on banks, or on the edge of 

 banks, illustrating the formation of barrier reefs and of atolls without 

 the introduction of subsidence. He instances many cases in which reefs 

 now growing will when awash form perfect atolls of large size, enclosing 

 deep lagoons, without any further deepening by solution. He also calls 

 attention to the great width of many of the existing fringing reefs, 

 which should show more signs of solution than they do if Murray's 

 theory is sufficient to account for the formation of the whole interven- 

 ing lagoon. The rotten state of the surface of all coral reefs, espe- 

 cially fringing reefs, shows that there is considerable solution as well as 

 removal of material going on ; but the very fact that the majority of 

 these reefs are of great width goes to show also that solution alone is 

 not active enough to remove great masses and form lagoons. The 

 case of Rodriguez is cited by Captain Wharton, where, although there is 

 a rise of tide of nearly six feet, with every facility for a scouring action 

 and rapid change of water, yet there is a fringing reef of a width of 

 nearly four miles and three quarters, intersected only by narrow shal- 

 low channels. In the case of the Florida Reef there is nothing to show 

 that the outside reef has not arisen on the southern edge of the Florida 

 Reef plateau, when it attained a depth at which corals can grow. The 

 lagoon between the reef and the keys was certainly never filled by 

 corals which have been carried away by solution, though it has been 

 occasionally obstructed by the growth of patches of corals, which are of 

 the same date or of a later growth than the coral reef proper. 



Dr. Coppinger 2 describes Amirante Bank as a submerged atoll, which, 



1 " Coral Formations," Nature, February 23, 1888, p. 393. 



2 Cruise of the Alert, by R. W. Coppinger, London, 1882, p. 225. In Florida 

 there is nothing to show that detached barrier reefs cannot grow up to reach the 

 constructive power of breakers, as Guppy seems to argue from the existence of 

 sunken barrier reefs. 



