256 APPENDIX. 



the shores of Southern Brazil, 1 and of the United States 

 from Long Island (as observed by Professor Rogers) to 

 Florida have the same character. Professor Rogers, in his 

 Report to the British Association (vol. iii. p. 13), speculates 

 on the origin of these low, sandy, linear islets ; he 

 states that the layers of which they are composed are too 

 homogeneous, and contain too large a proportion of 

 shells, to permit the common supposition of their formation 

 being simply due to matter thrown up, where it now lies, 

 by the surf: he considers these islands as upheaved bars 

 or shoals, which were deposited in lines where opposed 

 currents met. It is evident that these islands and spits of 

 sand parallel to the coast, and separated from it by shallow 

 lagoons, have no necessary connection with coral-forma- 

 tions. But in Southern Florida, from the accounts I have 

 received from persons who have resided there, the upraised 

 islands seem to be formed of strata, containing a good deal 

 of coral, and they are extensively fringed by living reefs; 

 the channels within these islands are in some places 

 between two and three miles wide, and five or six fathoms 

 deep, though generally 2 they are less in depth than width. 

 After having seen how frequently banks of sediment in the 

 West Indian Sea are fringed by reefs, we can readily con- 

 ceive that bars of sediment might be greatly aided in their 

 formation along a line of coast, by the growth of corals; 

 and such bars would, in that case, have a deceptive 

 resemblance with true barrier-reefs. 



1 In the London and Edinburgh Philosophical Journal \ 1S41, p. 257, 

 I have described a singular bar of sandstone lying parallel to the coast 

 off Pernambuco in Brazil, which probably is an analogous formation. 



2 In the ordinary sea-charts, no lagoons appear on the coast of 

 Florida, north of 26 ; but Major Whiting [Sillimans Journal, vol, 

 xxxv. p. 54) says that many are formed by sand thrown up along the 

 whole line of coast from St. Augustine's to Jupiter Inlet. 



