450 MEXICO, CENTEAL AMERICA, WEST INDIES. 



reckoning all the points of coral exposed at low water. Extensive basins or 

 sounds offer here and there perfectly sheltered anchorage, but for the most part 

 communicate with the open sea only through dangerous winding passages. 



The oval curve of the island is itself inscribed within a larger oval, which on 

 the south-west, west and north sides consists merely of submerged plateaux which 

 form a circular rampart against which the waves break ; the whole system thus 

 presents a dangerous circuit of coralline reefs, interrupted by a few " cuts," or 

 navigable openings. The Narrows, as the chief entrance is called, have a depth 

 of 26 feet, and give access from the north-east to the central basin, which has a 

 mean depth of 50, and, in the deeper cavities, of over 80 feet. 



The whole periphery of the outer banks, a distance of about 40 miles from the 

 Narrows to the southern convex side of the large island, presents at low water 

 nothing but three rocks, 8 to 10 feet high, rising like monoliths on a horizontal 

 ledge almost perfectly levelled by the action of the waves. Serpula3 grow in 

 countless masses on the outer edge of the reef, encircling it with a rampart which 

 resists the fury of the Atlantic billows. 



The various coralline groups composing the great mass of the plateau affect 

 the form of craters, hollow in the centre, and completely encircled by an elevated 

 rim. Like those of the Bahamas and the Pacific ocean, they are so many little 

 atolls grouped together in large systems, which merge in one vast complexity 

 of islands and banks, the atoll of atolls. The existence of coralline reefs under 

 such a high latitude, north of 32° N., or some 2,300 miles from the equator, is a 

 unique phenomenon due entirely to the influence of the Gulf Stream, which brings 

 the tepid waters of the Caribbean Sea, and with it the minute organisms that have 

 gradually built up the structure of the Bermudas in depths of 1,500 and 2,000, 

 and in one place even 2,500 fathoms. The climate, however, is too cold for some 

 species of coral-builders, which, nevertheless, are very common in the Bahaman 

 waters. The reefs themselves differ greatly in size, and are separated by shallow 

 troughs, and even by navigable channels. 



According to most naturalists, the Bermudan archipelago is one of those 

 whose phenomena agree best with the hypothesis of Darwin, who explains the 

 continuous growth of the reefs on banks several thousand feet high by the gradual 

 subsidence of the submarine pedestal. Certainly no change of level has taken 

 place since 1843, all the navigable channels having remained the same. But if 

 early records can be credited, the islands were much larger when first discovered 

 than at present. In 1870, when the great graving-dock was constructed in 

 Ireland Island, on the west side of the group, at nearly 50 feet below ebb tide, the 

 workmen came upon some peat and vegetable humus, which were exactly similar 

 to that on the surface of the existing islands, and which contained trunks of 

 "cedars," land shells, and the remains of birds. 



On the other hand, a relative upheaval may perhaps have taken place before 

 the subsidence, for the limestone cliffs of the islands exceed 160 feet in height. 

 Gibb'sHill, at the extreme southern bend of Great Bermuda, whence a panoramic 

 view is commanded of a labyrinth of wooded headlands and verdant flats, stands 



