146 CORAL FORMATIONS. 
alive, and adds that volcanic eruptions have probably destroyed them. 
The cold polar currents along the African coast, although generally 
leaving about fifteen degrees of latitude within the coral-reef seas, may 
at times close up and reduce it to still narrower limits. The same 
obstacle to the diffusion of species eastward, mentioned as occurring 
in the Pacific—that is, westerly currents—exists also in the Atlantic, 
and probably with the same effect. 
On the American shores of the Atlantic there are few reefs, except 
in the West Indies. The waters of the Orinoko and Amazon, and 
the alluvial shores they occasion, exclude corals from that part of the 
coast. But about Pernambuco, as I am informed by Mr. Titian R. 
Peale, there are some patches of growing corals, and they are said to 
extend along to 20° or 21° S. 
The Bermudas are of coral origin, and are the most northern point 
of growing reefs. 
In the West Indies, the reefs of Key West, Cuba, the Bahamas, 
and many of the eastern islands are well known. On the east coast 
of Florida they continue up as far as Cape Florida, in latitude 25° 
40’ N.: the west coast is free of them. ‘There are also said to be 
patches at intervals along the coast 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 everywhere without corals. They 
are within the influence of the Mississippi and other large rivers. 
We have thus seen that the earth is belted by a coral zone, corre- 
sponding nearly to the tropics in extent, and that the oceans through- 
out it abound in zoophyte reefs, wherever congenial sites are afforded 
for their growth. We have found that the currents of extra-tropical 
seas, which flow westward, and are interrupted and trended towards 
the equator by the continents, contract the coral seas in width, nar- 
rowing 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 cur- 
rents 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 and capes of the coast 
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 we have observed that there were no 
extensive reefs, except along eastern Africa; and, while other lands 
