270 CORALS AND CORAL ISLANDS. 



there are reefs at intervals, from the vicinity of Cape St. Roque 

 to the Abrolhos shoals in latitude i8°, as described by Prof. C. 

 F. Hartt, while reef corals extend south to Cape Frio. De- 

 scriptions of part of the Abrolhos reefs are given on page in. 

 North of the Abrolhos reefs, there are others of coral stretch- 

 ing on to Point Carumba ; again, off the Bay of Porto Seguro, 

 and across the Bay of Santa Cruz ; in the vicinity of Camamd, 

 around Quieppe Island ; along the shores of Itaparica Island ; 

 and at Bahia and Periperi ; then, after an interruption, oft 

 Maceio, in the vicinity of Pernambuco. Moreover the Roccas, 

 a cluster of reefs in the latitude of Fernando do Noronha, are, 

 as Hartt observes, probably of coral. 



It is thus seen that the earth is belted by a coral zone, 

 corresponding nearly to the tropics in extent, and that the 

 oceans throughout it abound in reefs, wherever congenial sites 

 are afforded for their growth. It has also been shown that 

 the currents of extra-tropical seas, which flow westward, and 

 'are interrupted and trended toward the equator by the con- 

 tinents, contract the coral seas in width, narrowing them to a 

 few degrees on the western coasts of the continents ; while the 

 tropical currents flowing eastward, diverge from the equator, 

 and cause the belt to widen near the eastern shores. The 

 polar currents flow also by the eastern coasts, preventing the 

 warmer waters from increasing the width of the coral zone as 

 much as it is contracted on the western coasts. Moreover, the 

 trend of the coast and its capes produce other modifications in 

 the direction of the currents, the most of which are apparent 

 in the actual distribution of coral reefs. On the shores of 

 the continents it is observed that there are few extensive reefs, 

 and the coasts on which they occur are those which, owing to 

 the dryness of the climate, have no great rivers to pour fresh 

 water and detritus into the sea. Thus the influence of con- 

 tinental waters and detritus on the distribution of reefs, is 

 shown to be very marked. But about the Pacific Islands, 

 where streams are small, the same cause has had little effect, 

 seldom doing more than modifying somewhat the shores and 



