12 bulletin: museum of compaeative zoology. 



large accumulations of sediment are in progress on the West Indian 

 shores, . . . especially of the portion north ^ of a line joining Yucatan 

 and Florida. The area of deposition seems less intimately connected 

 with the debouchement of the great rivers than with the course of the 

 sea currents, as is evident from the vast extension of the banks from the 

 promontories of Yucatan and Mosquito." Darwin considers the iso- 

 lated banks, such as the Misteriosa Bank, the bank off the northern point 

 of Old Providence, Thunder Knoll, and others of various dimensions, to 

 be " composed of sand firmly agglutinated, with little or no coral." He 

 considers their steep slopes as characteristic of similar banks " in all 

 parts of the world where sediment is accumulating, , . . the banks 

 shelving very gently far out to sea, and then terminate abruptly. . . . 

 The form and composition of the banks in the middle parts of the West 

 Indian sea clearly show that their origin must be chiefly attributed to 

 the accumulation of sediment ; and the only obvious explanation of their 

 isolated position is the presence of a nucleus round which tlie currents 

 have collected fine drift matter." Further he says, " There cannot be 

 any doubt that the' Mosquito Bank has been formed by the accumulation 

 of sediment round the promontory of the same name." And, finall}', he 

 says that the origin of the Bahama banks " is easily explained by the 

 elevation of banks fringed on their windward side by coral reefs." But 

 he modities this assertion by stating that the Bahamas, as well as many 

 of the submerged banks of the West Indian sea, " have been woi'u down 

 by the currents and waves of the sea during their elevation." 



From what we have learned of the geology of the West Indian sea- 

 shores, there is nothing to confirm Darwin's views of the formation of 

 great accumulations of sediment against the promontories of Yucatan or 

 of Mosquito. The great submarine plateaus off those coasts consist of 

 the seaward continuation of their shore strata, and not of accumulations 

 of sediment. Whatever loose particles compose the bottom on these 

 plateaus are due to the remains of the animals and plants thriving upon 

 them, and flourishing to an unusual degree from the mass of pelagic 

 life brought to serve them as food by the prevailing currents and winds. 

 The currents, while they bear but little sediment in suspension, on the 

 contrary carry along a pelagic fauna and flora unsurpassed in richness, 

 but which stipplies a comparatively small amount of material towards the 

 building up of the submerged West Indian banks compared to that fur- 

 nished by the carcasses of the animals and plants fed by this pelagic 

 material, and the remains of which supply the great bulk of the deposits 

 which go to build up these banks. 



* This must be a misprint for " east." 



