300 CORALS AND CORAL ISLANDS. 



rious voyages with those of the Expedition, the author has 

 been enabled to draw these boundary lines with a consider- 

 able degree of accuracy, and they are laid down upon the chart 

 of the world published in his Report (Wilkes Exploring Ex- 

 pedition) on Geology, and, with other isocrymal lines, on a 

 full isocrymal chart of the globe, in his Report on Crustacea, 

 from which it was reproduced in volume xv. (1853) of the 

 second series of the American Journal of Science, which is now 

 again issued at the close of this volume. 



In the Pacific Ocean, this coral boundary, or isocryme of 

 68°, excludes the Galapagos from the coral seas, making a 

 bend around them, and passing for a short distance even 

 north of the equator, instead of near the parallel of 28° 

 south, its position in mid-ocean. 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. 

 70^°, 11\° 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. 



On the side of Asia the boundary line bends far southward, 

 and reaches the coast of Cochin China within 15° of the 

 equator, although 30° from the equator a little to the east- 

 ward. On the west side of the Atlantic, the northern line 

 starts at Cape Florida, in latitude 15° N., stretches abruptly 

 northward, and bends around the Bermudas in latitude 33° 

 N. On the African coast opposite, the northern line curves 

 downward to the latitude of the Cape Verds, and the south- 

 ern upward nearly to the equator. The following table gives 

 the positions of the coral boundary lines where they meet 

 the coasts of the continents. 



