AGASSIZ: BAHAMAS. 87 



of seolian hills covering the island. These hills rise to a height of from 

 a hundred to a hundred and forty feet, and are covered with woods. 



An examination of the map of Watling Island is interesting as show- 

 ing the great number of lagoons which occupy so large a part of its 

 surface. On the western side is found the largest of these lagoons. 

 It is quite shallow, the part we examined varying between one and a 

 half and three feet in depth. An artificial cut has been made through 

 a low ridge separating one of the western lagoons, about half a mile from 

 Riding Rock beach, so as to make a boat passage to the larger lagoon 

 and reach by water the vicinity of the lighthouse on the northeastern 

 extremity of the island. The cut shows the same seolian structure of 

 the rock so characteristic of the islands we had so far visited. In the 

 distance, on the opposite side of the lagoon, could be seen rising the 

 same solidified seolian hills which characterize the structure of all the 

 islands on the larger banks. The examination of this side of Watling 

 Island plainly shows its structure to be similar to that of the islands 

 to the westward, and also shows that "Watling owes its present config- 

 uration and the existence of its many lagoons to the subsidence which 

 has caused the gradual disappearance of the extensive tracts of seolian 

 land which once covered the greater pai't of the Bahama Banks. 



The bottom of the great lagoon is thickly covered with algae (Ace- 

 tabularia), and the shores of its beaches are lined with diminutive speci- 

 mens of the same species of shells found on the open sea beaches. The 

 water of the lagoon is intensely salt. It connects evidently with the sea, 

 as our guide mentioned several blow-holes through which the tide is 

 foi'ced into the lagoons. 



The shores of the lagoon are lined with mangroves. Parts of the 

 lagoon have been separated from the sea by a high narrow beach thrown 

 up by the incessant Atlantic swell ; but by far the greater number of 

 the lagoons of Watling Island are due to the general subsidence of 

 the island, forming drainage areas, and allowing the sea to cover the 

 fiats intervening between the ranges of seolian hills and then to the 

 closing of these openings by coral sand beaches thrown up by the sea. 

 Many of the ponds are disconnected, are salt, and are supplied by per- 

 colation through the barriers separating them from the sea, or by blow- 

 holes connecting them directly with it. This is especially the case 

 with some of the ponds only separated from the sea by narrow beaches, 

 Many of the lagoons are in underground communication with the sea. 

 and in some of them the position of the blow-holes through which the 

 sea water is forced up can be traced by the commotion of the water of 

 parts of the lagoon. 



