THE BAHAMA ISLANDS 19 



may be seen on Green Cay (Plate VI, Fig. 1, and Plate VII), near the elevated 

 coral reef spoken of above. By an examination of these figures it wiU be seen 

 that the^thin-bedded coral rock in the foreground has been ripped up in huge 

 slabs and piled in a rampart along the upper margin of the beach. An 

 ancient one of these ramparts which have been recemented into solid rock by 

 the accumulation and consolidation of coral sand is shown (Plate VI, Fig. 2). 



TOPOGRAPHIC HISTORY. 



It is stated above that the Bahama Islands are honey-combed with 

 caverns. This could only have taken place when the Islands stood higher 

 than they do to-day. Terrestrial and marine ocean-holes together with banana- 

 holes and brackish-water lakes are different lines of evidence showing that 

 the sea has ready access to the interior of the Islands. This access is easily 

 possible through the presence of these underground caverns. The deepest 

 ocean-holes extend down some 300 feet beneath the surface of the water. This 

 indicates that the Islands must have stood at least 300 feet higher when this 

 excavation took place than they do to-day. The present attitude of the archi- 

 pelago then is indicative of subsidence. The evidence furnished by the elevated 

 coral reef on Green Cay, together with the elevated deposits carrying marine 

 shells and the raised sea-cliffs, shows that the Islands have been elevated from 

 10 to 25 feet at no very remote date. 



So far as geological evidence is able to throw light on the problem, it is 

 evident that the topographic history of the Islands has been as follows : there 

 was a period of elevation when the Islands stood at least 300 feet higher than 

 they do at the present time. During this epoch the dry land area of the 

 Bahamas was very much greater than to-day. The extent of this land mass may 

 be approximately reconstructed by imagining all the light-colored areas which 

 now constitute the banks as standing above water level. (Plate X.) It will be 

 seen then that the Islands as they exist to-day are mere remnants of what they 

 were formerly and that the great reduction in land surface has been due to 

 the effects of subsidence and marine erosion. During this period of elevation 

 the limestone rock was dissolved into caverns and grottoes, similar to what 

 exists now in the Shenandoah Valley and Florida. This period of elevation 

 gave place to one of depression, when the land sunk beneath the level of the 

 ocean to a position at least 15 feet lower than it now occupies. During this period 

 the deposits bearing marine shells were made as well as the coral reef on Green 

 Cay, and the ancient sea-cliffs were cut. The third chapter in the topographic 



