CORALS. 127 



for the luxuriant growth of these animals. The situation of mountains on or near the 

 coast of the continents or elevated islands, and the direction in which the rivers of 

 such flow to the ocean, also has its influences on the distribution of coral islands in the 

 immediate vicinity. One of the very best illustrations of this limitation of coralline 

 life is seen in the island of New Caledonia. Most of the livers in this large island, 

 according to Dana, empty theniselves into the ocean along the western coasts, while 

 the eastern side is almost wholly destitute of streams of fresh water. Along the 

 eastern border we find an almost continuous coral reef, and no signs of coral growth 

 on the western. Fresh water is destructive to coral life, and rivers bring from the 

 land large quantities of silt, which is also detrimental to its growth. To these causes 

 may perhaps be traced the almost total absence of coral formations on the northern 

 border of South America, near those parts of the coast line where the Amazon and 

 Oronoco pour their great volumes of fresh water into the Atlantic. 



There are several very curious facts, many of which are not yet explained, in 

 regard to the geographical distribution of genera of corals. The coral fauna, for 

 instance, of the Bahamas and Florida regions is widely different from that known to 

 exist on the western coasts of Central America. The corals of the latter region have a 

 closer likeness to those of the Indian Ocean, almost its antipodes as far as geographical 

 position goes, than they do to those of the Caribbean Sea, separated from them by 

 only the narrow isthmixs of Darien. Madrepora cervicornis, a most abundant coral 

 along the Florida Keys, is very rare in the Bermudas. 



Corals are found at almost all depths in the -ocean. The greatest profusion of 

 life lies in the zone between the surface and the depth of one hundred to one hundred 

 and fifty feet. Deep sea corals, of an interesting character from their relationships 

 with extinct genera, are found at great depths, even in the abysses of the ocean. 



The general distribution of coralline life in the different oceans is as follows : — 



The Atlantic Ocean has several very considerable coral reefs and coral islands, all 

 of which are confined to its western border. In the South Atlantic a large and peculiar 

 reef is found extending many miles along the southeast coast of Brazil. In the 

 chain of islands called the Lesser Antilles we find that the frequency of coral reefs 

 increases as we go towards the northern members. Along the northern shores of San 

 Domingo, Hayti, and Cuba, we find extensive reefs. There are evidences also of 

 elevated coral banks in these islands. The peninsulas of Yucatan and Honduras 

 ai"e fringed with coral shoals, and large banks exist on their northeastern and northern 

 borders. The line of Florida coral reefs, extending from Loggerhead Key, the 

 extreme western island of the Tortugas, to the southern extremity of the peninsula of 

 Florida, is one of the most instructive collections of coral islands in the Atlantic 

 region. The Bahama Islands are composed wholly of coral, and are the largest con- 

 tinuous bank of growing coral in the North Atlantic Ocean. Its extension is as great 

 in length as the whole eastern coast line of the United States from Maine to Florida. 

 The only example of an oceanic coral island in the North Atlantic is the Bermuda 

 group, which lies in the latitude of Charleston, S. C, about seven hundred miles from 

 Cape Hatteras, the nearest land. This reef is one of the most interesting, from the 

 fact that it is in the highest latitude in which corals are known to flourish with any 

 vigor, an exception which is probably the result of the sheltering action of the well- 

 known Gulf Stream. The most extensive coral plantations are found in the Pacific 

 and Indian oceans. On the eastern border of the former they are, however, very 

 insignificant, , Worn fragments of coral are found on the Galapagos, and Col. Grayson 



