12 PHYSIOGRAPHY AND GEOLOGY 



Character of Surface. The topography of these land fragments consists of 

 features which rise in relief and others which sink as depressions beneath the 

 general surface. The features of relief are dunes of coral sand and ridges of 

 hard rock. The depressions consist of lakes, ponds or marshes, ocean-holes, 

 banana-holes, and a general rough surface. 



Dunes occur with great frequency along the sea-shores, where the winds 

 have an opportunity to blow the calcareous sand up into heaps dazzling in the 

 sunlight. These bear the characteristic vegetation and consolidate rapidly 

 into soft rock, so that the tendency is to grow in height rather than to migrate 

 inland. These dunes are distributed generally throughout the archipelago, but 

 perhaps they arc well developed as anywhere along the eastern side of Eleuthera 

 fronting the ocean. There appears to be no very well defined line of separation 

 between these half consolidated dunes, and the ridges of hard rock. Both have 

 the same origin, as well as a similar topography, and one passes into the other 

 with insensible gradations. The oldest dunes are hard rock, while the youngest 

 arc loose sand, and there is every intermediate stage. These ridges cross the 

 islands in ranks like the dunes, and where an island has suffered severely from 

 erosion, are frequently the only remaining features to mark the once more con- 

 tinuous land surface. The highest of these ridges are met with in Cat Island, 

 where they rise to about 400 feet, but this is uncommon. They are usually low, 

 rolling hills, scarcely high enough to break the monotony of the landscape. 



SUB^RIAL DIVISION. 



Professor Agassiz has given such minute and careful descriptions of the 

 various islands of the Bahama archipelago, 12 that it is unnecessary to go over 

 the same ground here. Those desiring detailed descriptions are referred to the 

 monograph mentioned above. In this paper only the salient features which 

 apply to the group as a whole will be considered. 



Classification. The Bahama Islands consist of some three thousand or 

 more islands, keys, and rocks, which Agassiz has classified in the following 

 manner : 13 



First, sunken banks like the Navidad, Silver and Mouchoir Banks; second, 

 islands occupying the whole or nearly the whole summit of 'the banks from 

 which they rise, as Watlings, Rum Cay, Concepcion, Plana Cays, Inagua, and 

 the atoll of Hogsty; third, banks having a resemblance to atolls, like Crooked 



12 Loc. cit. 



13 Loc. cit., p. 11. 



