STRUCTURE OF CORAL ISLANDS. 



137 



land is but seventy-six miles, or less than one twenty-fourth. 

 In the Caroline Archipelago the proportion of land is still 

 smaller. Menchikoff atoll covers an area of 500 square miles, 

 and includes hardly six square miles of wooded land. In the 

 Marshall Islands the dry land is not over one-hundredth ot 

 the whole surface ; while in the Pescadores the proportion ot 

 land to the whole area is about as i to 200. 



The distribution of the land upon the reef is obvious from 

 the sketches already given. It is seen, as long since remarked, 

 that the windward side is, in general, the highest. It is also 



MENCHIKOKF ATOLL {^^ OK AN INCH TO A MILE). 



apparent that there are not only great irregularities of form, 

 but that on one side the reef may at times be wholly wanting 

 or deeply submerged. 



In many islands there is a ship-entrance through the reef, 

 sometimes six or eight fathoms deep, to the lagoons, where 

 good anchorage may be had ; but the larger part have onl) 

 shallow passages, or none at all. In the Paumotus, out of the 

 twenty-eight^ visited by the Expedition, not one-half were 

 found to have navigable entrances. In the Carohnes, where 

 the islands are large and not so much wooded, entrances are 

 of more common occurrence. About half of the Kingsmill 

 Islands afford a good entrance and safe anchorage. Through 

 these openings in the reefs, there is usually a rapid outward 

 current, especially during the ebbing tide. At Depeyster 



