18 A NATURALIST OX THE "CHALLENGER. 



Bermuda, April 5tli to 21st, and May 2Jth to June 12th, 18*J3. 



— Bermuda is entirely a coral island, that is to say, the complete 

 mass of the island now above water, and that below sea level, as 

 far at least as excavations which have been made have extended, 

 has been brought together by the agency of lime-secreting animals 

 and plants, aided by the winds and waves, and alterations in the 

 height of the sea-bed. It is the most distant coral island from 

 the equator, lying about 9° of latitude north of the Tropic of 

 Cancer, in about the same latitude as Madeira, which island has, 

 however, no coral reefs. It is distant from Cape Hatteras, the 

 nearest point of the American coast, about 600 miles. 



Bermuda consists of a series of islands, some very small 

 indeed, others several miles in length, there being, it is said, an 

 island for every day in the year. The islands are disposed in an 

 irregular semicircle, and the larger ones of the chain are narrow 

 and elongate in form. This semicircle or rather semiellipse is 

 completed below water, or made into an entire atoll shape by a 

 series of coral reefs, as may be seen by a glance at the chart. A 

 few narrow and winding passages lead in through the reefs to the 

 harbours of St. George's, Ireland Island, and Hamilton the 

 capital town. The highest point is only about 300 feet above 

 the level of the sea. 



The islands are almost entirely composed of blown cal- 

 careous sand, more or less consolidated into hard rock. In 

 several places, and especially at Tuckers-town and Elbow Bay, 

 there exist considerable tracts covered with modern sand dunes, 

 some of which are encroaching inland upon cultivated ground, 

 and have overwhelmed at Elbow Bay a cottage, the chimney of 

 which only is now to be seen above the sand. The constant 

 encroachment of the dunes is prevented by the growth upon 

 them of several binding plants, amongst which a hard prickly 

 grass (Cenchrus) with long, deeply-penetrating root fibres, is the 

 most efficient, assisted by the trailing Ipomcea pes caprce % 

 When these binding plants are artificially removed, the sand at 

 once begins to shift, and the burying of the house and the 

 present encroachment at Elbow Bay are said to have originated 

 from the cutting through of some ancient sand-hills for military 

 purposes. 



