258 APPENDIX. 



remarked that some atoll-like reefs probably did exist, which 

 had originated in the manner here supposed. 



Proofs of elevation within recent tertiary periods abound, 

 as referred to in the sixth chapter, over nearly the whole area 

 of the West Indies. Hence it is easy to understand the origin 

 of the low land near those coasts where sediment is now ac- 

 cumulating ; for instance, on the northern part of Yucutan, and 

 on the N.E. part of Mosquito. Hence, also, the origin of the 

 great Bahama banks, which are bordered on their western and 

 southern edges by narrow, long, singularly-shaped islands, 

 formed of sand, shells and coral-rock, some of them being 

 about a hundred feet in height, is easily explained by the ele- 

 vation of banks fringed on their windward sides by coral-reefs. 

 On this view, however, we must suppose either that the great 

 Bahama sand-banks were all originally deeply submerged, and 

 were brought up to their present level by the same elevatory 

 action which formed the linear islands ; or that during the 

 elevation of the banks, the superficial currents and swell of 

 the waves wore them down, and kept them at a nearly uniform 

 level. But this level is not quite uniform ; for in proceeding 

 from the N.W. end of the Bahama group towards the S.E., the 

 depth of the banks increases, and the area of land decreases, 

 in a very gradual and remarkable manner. The view that 

 these banks have been worn down by the currents and waves 

 of the sea during their elevation, seems to me the most prob- 

 able one. This view is also, I believe, applicable to many of 

 the submerged banks, in widely distant parts of the West 

 Indian sea ; for, on any other view, the elevatory forces must 

 have acted with astonishing uniformity. 



The shore of the Gulf of Mexico, for a space of many 

 hundred miles, is formed by a chain Of lagoons, from 1 

 to 20 miles in breadth (Columbian Navigator, p. 178, 

 &c), containing either fresh or salt water, and separated 

 from the sea by linear strips of sand. The shores of southern 

 Brazil, and of the United States from Long Island (as 



