THE BAHAMAS AND BERMUDAS 297 



derived marine sediments, mixed with the calcareous 

 debris of the life of the ocean's slopes." Professor Hill 

 was also able to trace a post-Tertiary folding in the older 

 limestones, and so establish an unconformity between 

 the older limestone and the modem reef rock, which 

 separated them into two distinct systems. From all of 

 which we seem led to the interesting conclusion that 

 the reef -building corals have played a far smaller part 

 in the formation of the terraces of Cuba than was pre- 

 viously supposed. 



Agassiz found that the Bahamas, as far as Turk's 

 Island, were of geolian origin. They were formed at a 

 time when the banks must have been one huge irregu- 

 larly shaped mass of lowland. From the sand of its 

 great sea beaches, successive ranges of dunes were blown 

 up, such as are still found at New Providence, which 

 the action of the rain and spray has hardened into seolian 

 rock. 



He assumed that the " ocean holes " which he sur- 

 veyed on the bank were made above water, and are 

 similar to the holes found in the seolian rocks on land, 

 and concluded that the Bahamas have subsided about 

 three hundred feet since the formation of the seolian 

 land. During this subsidence the wasting forces of the 

 sea and air have little by little eaten away the land, 

 leaving only here and there narrow strips in the shape 

 of the present islands. The modern coral reefs form 

 but a very insignificant part in the topography of the 

 islands and have had nothing to do with the building 

 up of the islands beyond filling here and there a 

 bight or a cove with more modern reef rock, and they 

 form but a comparatively thin coating on the seolian 

 rock. 



