MODERN CORAL REEFS 



387 



by the seaward growth of the front of the reef and the enlargement 

 by sokition of the channel between the reef and the land without sub- 

 sidence (Murray, Agassiz), and, finally, by the independent upward 

 growth of the corals into reefs on a suitable platform at a distance 

 from the shore. The Great Barrier Reef on the northeast coast 

 of Australia extends for 1.250 miles from Torres Strait in 9.5° S.. 

 lat. to Lady Elliott Island in 24° S. lat. At Cape York the sea- 



FiG. T2,. Barrier reef around cen- 

 tral island. The surf (white) 

 shows the location of the reef, 

 which is dotted with small coral 

 islands. (After Le Conte.) 



Fig. 74 Diagrammatic section of the 

 island shown in the preceding 

 figure, showing location of reefs 

 (dotted). (After Le Conte.) 



ward edge of this reef is nearly 90 miles distant from the coast and 

 it descends to a depth often exceeding 1,800 feet. It represents "a 

 great submarine wall or terrace, fronting the whole northeast coast 

 of Australia, resting at each end in shallow water, but rising from 

 very great depths about the center. Its upper surface forms a pla- 

 teau, covered by 10 to 30 fadioms of water, but studded all over 

 with steep-sided block-like masses which rise up to low water 

 level." ( Jukes-Browne-53 ; 54.) These individual reefs are espe- 



FiG. 75. An atoll formed of discon- 

 nected coral islands arising from 

 a submerged reef which is out- 

 lined by surf (white). (After 

 Le Conte.) 



Fig. yG. Diagrannnatic section of an 

 atoll, showing depth of central 

 lagoon, and relation of the islands 

 to the reef. (After Le Conte.) 



cially numerous along the edge of the bank and protect the com- 

 paratively shallow water over the reef, as well as the numerous 

 inner reefs scattered over the surface, from the effects of the waves 

 of the open Qcean. In most barrier reefs, the outer ^<\g& is in 

 places often awash at low tide and islands and bars of dead coral 

 and sand are formed. These may coalesce and in time become cov- 

 ered with vegetation. Thus a strip of land is formed, lying some 

 hundred yards or less from the extreme outer edge of the. reef. 



