Contribnti{jns to the Fauna of I he Bahamas 



11 



least making- the separating channels so narrow that they would not form any con- 

 siderable obstacle to the invasion of the majority of land animals. It must be re- 

 membered that the Great Bahama Bank, though to great extent submerged would be 

 converted by an elevation of only 10 fathoms into a large land mass, separated 

 from Cuba by a narrow channel, and that a further elevation of about 200 fathoms would 

 connect it with Cuba. For a connection with Florida an elevation of about 400 

 fathoms would be necessary. By such temporarj^ connections with öfter lands the 

 character of the land fauna would be much altered : it would no longer be that of 

 a true oceanic island. To trace the topographical history of the islands since their 

 formation is therefore of great importance. Owing to the geological researches that 

 at several times have been made in the Bahamas, 1 think it possible with a high 

 degree of certainty, to answer this 

 question. Agassiz has given the first 

 real help towards settling tliis problem. 

 He writes (op. cit. p. 7): »After the 

 formation of the islands came an ex- 

 tensive gradual subsidence, which can 

 be estimated at about three hundred 

 feet», an opinion which is based on the 

 observation of some oceanholes having 

 a depth of 34 fathoms. He takes these 

 holes to be »submarine blow holes or 

 canons in the eeolion limestone ol' the 

 Bahama hills when they were at a 

 greater elevation than now.» During 

 the subsidence that must have taken 

 place since the formation of these 

 holes, the islands were exposed to a 

 great erosion. The level at which the 

 Bahamas once stood, according to 

 Agassiz, would be high enough to make the Great Bahama Bank a mass of land, 

 but not high enough to connect it with Cuba, as is evident from the statements 

 about the depths given above. I think however, it is not quite certain that the 

 Bahamas at that time had such a large extension, for it is evident that during the 

 subsidence the islands were not only eroded but with all probability also built higher 

 up. Coral sand must have been deposited on the beaches even during this time and 

 piled up to hills in the interior. The islands were reduced in extension, but 

 increased in height, measured from the ground, not from the sea level. Agassiz's 

 proof that the islands were once higher than at pi-esent time is, it is true, quite 

 correct, but it does not show, as far as I can judge, that the level stated was the 

 highest at which the Bahamas ever have stood. It is possible that other ocean- 

 holes, deeper than that mentioned, will be found, showing that the islands have 



Fig. A. Eroded limestone- rock (after Agassiz). 



