On Coral Reefs and Islands. 349 
On the American shores of the Bieri there are few reefs, 
except in the West Indies. The waters of the Orinoco and 
Amazon, and the alluvial shores Si occasion, exclude corals 
from that part of the coast. But about Pernambuco, as I am in- 
formed by Mr. Titian R. Peale, there are some peietin’ a grow- 
ing he Berni and they are said to extend along to 2U° or 21° S. 
fs. 
In the West Indies, the reefs of Key West, Cuba, the Baha- 
mas, and many of the eastern islands are well known. On the 
east coast of Florida they continue Re as far as Cape eee in 
latitude 25° 40’ N.: the west coast is free of them. There 
also said to be patches at intervals “ime the coast of Vea 
and Guatemala; but the west shores of the Gulf of Mexico, as 
well as the northern, like West Florida, are mostly low, and eve- 
rywhere without corals. They are within the influence of the 
eeneae” and other large rivers. 
“We have thus seen that the earth is belted by a coral zone, 
co rrespouding nearly to the tropics in extent, and that the oceans 
throughout 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, aud are interrupted 
and trended towards the equator by the continents, 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 eqnator 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 eon zone as much as it is contracted on the 
Western coasts. Moreover, the trend and capes of the coast pro- 
duee other read Semtsons in the direction of the currents, the 
0 
there are no extensive reefs, except along eastern Africa; and, 
while other lands abound in rivers, this African coast has only 
Some small streams. Thus the influence of continental waters 
and detritus on the distribution of reefs, has been shown to be 
have ascertained that in different groups, as the Ladrones, 
the Sandwich Islands, Samoa, New Hebrides, there is an inverse 
voleanie action in the island; and that the largest reefs exist _ 
where there is no peek of former igneous action, or where it has 
long ceased. The ad merye anironee WY volcanic agency to the 
\ 
» 
