DISTRIBUTION OF REEFS, 135 
a divergence. From a comparison of the thermometrical observations 
of various voyagers with those of the Expedition, I have been enabled 
to draw this coral boundary with a considerable degree of accuracy ; 
and it is laid down upon the chart of the world accompanying this 
volume. In the Pacific it is observed to exclude the Galapagos,* 
and reach the South American coast xorth of the equator, instead of 
at the parallel of 28° S., the position in mid-ocean. On the coast of 
Asia it curves from the equator beyond latitude 30°. In the Atlantic it 
forms an abrupt bend far to the north, in the line of the Gulf Stream, 
and includes the Bermudas in latitude 32° N.; while on the African 
coast the northern line curves downward to the latitude of the Cape 
Verds, and the southern upward nearly to the equator. The following 
table will give more definitely the position of the coral boundary line 
where it meets the coasts of the continents. 
Pacific Ocean. Atlantic Ocean. 
East side of ocean—Northern, Latitude 21° N. Latitude 10° N. 
Southern, 4° N, 5° 8, 
West side of ocean—Northern, 34° N. 34° N. 
22° 8, 
30° S., New Holland. 
Southern, 29° S., Africa. 
It follows from the above, that while the coral-reef seas are about 
fifty-six degrees wide in mid-ocean, they are 7 the Pacific seventeen 
degrees wide on the west coast of America, and sixty-four degrees on 
the Asiatic side. In the Atlantic, they are about fifteen degrees wide 
on the African coast, and fifty-six degrees on the coast of America. 
If we reckon to the extremity of the bend in the Gulf Stream, the 
whole width off the east coast of America, north of the equator, will 
be over forty degrees. It is obvious that these facts enable us to ex- 
plain many seeming anomalies in the distribution of coral reefs. 
Within the limits included by the coral-reef boundary line, those 
other causes operate which influence the distribution of reefs. The 
effect of a deep, abrupt coast has been pointed out. ‘The unfavourable 
character of sandy or muddy shores, and the action of detritus, marine 
currents, and fresh waters, have also been stated. 
* Captain Fitzroy, R. N., found the surface temperature of the sea at the Galapagos, 
from Sept. 16 to Oct. 18, 1835, 62° to 70° F. Oct. 23, in lat. 0° 30’ S., and long. 99° 
4' W., the temperature of the sea was 66° F. Oct. 24, lat. 0° 23’ N., long. 96° 53' W.., 
temp. 704°, 714° F. While under the equator, about the middle of the Pacific, the 
range of surface temperature of the sea through the year is 81° to 88° F. 
