50 THE BERMUDA ISLANDS. 



On the lagoon side of the ring the shore-platform is very 

 commonly replaced by a gently sloping sand bottom, with or 

 without the formation of a true beach area. Frequently there 

 juts out from the shore a growing reef-platform (upon which 

 the coral growth is fairly profuse), which descends with a 

 vertical or overhanging edge to a second deeper zone of coral 

 life. Over the bottom, which presents a more or less uniform 

 character, coral sand and debris, calcareous pebbles, the tests 

 of various Foraminifera, etc., are extensively distributed, form- 

 ing there a sticky white or bluish paste, much like that which 

 extends for miles beyond the outer border of the forming reef. 

 The depth of the lagoons varies from a few feet to twenty or 

 thirty fathoms, as we find it in many island groups of the 

 Pacific (Paumotu, Gilbert's Group, Keeling Island, etc.). In 

 the Maldives it exceptionally attains 50 and GO fathoms. 



As reef-building corals cannot long survive exposure to the 

 atmosphere it is manifest that the upper limit of the growing 

 mass will be the actual surface of low-water. In the line of 

 the breakers, or in the shallows just beyond, the coral polyps 

 thrive in their greatest profusion, and the almost end- 

 less variety of their forms, not less than their brilliant color- 

 ing, never fails to arouse the wonder and enthusiasm of the 

 traveler. Prof. Dana thus graphically describes the forming 

 island : " The reef of the coral atoll, as it lies at the surface 

 still uncovered with vegetation, is a platform of coral rock, 

 usually two to four hundred yards wide, and situated so low 

 as to be swept by waves at high tide. The outer edge, directly 

 exposed to the surf, is generally broken into points and jagged 

 indentations, along which the waters of the resurging wave 

 drive with great force. Though in the midst of the breakers, 

 the edge stands a few inches, and sometimes a foot, above 

 other parts of the platform ; the incrusting nullipores cover it 

 with varied tints, and afford protection from the abrading 

 action of the waves. There are usually three to five fathoms 

 water near the margin ; and below, over the bottom, which 

 gradually deepens outward, beds of coral are growing pro- 



