SA L T KE Y BA NK. 1 79 



Prof. Agassiz gives the following account of a part of these 

 reefs in the first volume of the *' Bulletin of the Museum of 

 Comparative Zoology:" — 



"The Bahamas and the reefs to the north-east of Cuba 

 exhibit very abrupt slopes, and a great depth is reached close 

 to the shores of the Banks, so that the Bahamas resemble the 

 coral reefs of the Pacific much more than the reefs of the coast 

 of Florida. 



"The whole group of banks and keys embraced between 

 Double-Headed Shot Key, Salt Key, and Anguilla Key (all on 

 the Salt Key Bank) is a very instructive combination of the 

 phenomena of building and destruction. The whole group is 

 a flat bank covered by four or five, and occasionally six, 

 fathoms of water, with fine sandy bottom, evidently corals 

 reduced to oolitic, the grains, which are of various sizes, from 

 fine powder to coarse sand, mingled with broken shells, among 

 which a few living specimens are occasionally found. The 

 margin of the Bank is encircled on several points by rocky 

 ridges of the most diversified appearance, and at others edged 

 by sand-dunes. A close examination and comparison of the 

 different Keys show that these different formations are in fact 

 linked together, and represent various stages of the accumula- 

 tion, consolidation, and cementation of the same materials. 

 On the flat top of the bank the loose materials are pounded 

 down to fine sand ; in course of time this sand is thrown up 

 upon the shoalest portions of the Bank, and it is curious to 

 notice that these shoalest parts are its very edge, along which 

 corals have formed reefs which have become the basis of the 

 dry Banks. The foundation rock, as far as tide, wind, and wave 

 may carry the coarser materials, consist of a conglomeration 

 of coarser oolitic grains, rounded fragments of corals, or 

 broken shells, and even larger pieces of a variety of corals 

 and conchs, all the species being those now found living upon 

 the Bank, among which Strouibiis gigas is the most common 

 besides that, Astraie {Orbicella) aimularis, SiderasircBa siderea 

 and McBandriiia mammosa prevail. The shells of Strombus are 

 so common that they give great solidity and hardness to the rock. 



N 2 



