352 CORALS AND CORAL ISLANDS. 
of Venezuela and Guatemala; but the west shores of the Gulf ~ 
of Mexico, as well as the northern, like West Florida, are 
mostly low, and without reefs ; they are within the influence 
of the Mississippi and other large rivers. Some species of 
reef corals, however, occur in the vicinity of Aspinwall (p. 
ig) 
South of the equator, on the east coast of South America, 
there are reefs at intervals, from the vicinity of Cape St. 
Roque to the Abrolhos shoals in latitude 18°, as described by 
Prof. C. F. Hartt, while reef corals extend south to Cape Frio. 
Descriptions of part of the Abrolhos reefs are given on page ~ 
140. North of the Abrolhos reefs, there are others of coral 
stretching on to Point Carumba; again, off the Bay of Porto 
Securo, and across the Bay of Santa Cruz; in the vicinity of 
Camamt, around Quieppe Island; along the shores of Ita- 
parica Island; and at Bahia and Periperi; then, after an in- 
terruption, off Maceid, in the vicinity of Pernambuco. More- 
over the Roceas, 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 equa- 
tor, 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 
