160 Couthouy on Coral Formations 



that the absence of coral on the other side of the continent^ 

 and in the wide space between it and the low islands of 

 Polynesia, is to be attributed to the prevalence of cold cur- 

 rents, which proceeding northward from the Polar regions are 

 perceptible the whole distance from Cape Horn to Callao, and 

 I presume much further to the north, in a temperature of the 

 ocean too low for the existence of the coral animals, and that 

 in a similar low temperature we are to seek for the cause of 

 their absence at the Cape Verde Islands. I have already al- 

 luded to the^greater heat on the souihern part of our coast and 

 the Bahamas, produced by the vicinity of the Gulf Stream. 



A like temperature prevails along the southern shore of Cu- 

 ba, and the islands in its vicinity, and though unable to speak 

 positively, from^having no data, as to the Bermudas, I have no 

 doubt from their proximity to the Gulf Stream, that they are 

 washed by an equally warm sea. Now let us glance for a 

 moment at the facts bearing on this question, in regions situ- 

 ated in corresponding parallels of latitude, where no coral 

 formations exist. At Valparaiso, in lat. of 33° south, and 

 thence as far as the 20th parallel, in the month of November, 

 the surface temperature of the ocean near the coast has been 

 found to range from 58° to 60° ; at Callao, in the lat. of 12°, 

 from 58° to 62°, and thence in a north-westerly direction to 

 the GalapagoSj'to increase gradually to 68° and 70°. Among 

 these islands, at the same season, its average was not above 

 68°, and at some of them it did not exceed 62°. But leaving 

 these islands and proceeding south-west, we find it steadily 

 rising, till on the skirts of the Dangerous Archipelago it is up 

 to 78° and 79°, nearly 20° higher than on the coast in the 

 same parallel. And here we enter upon the coral formations. 

 Among the Paumotus, the field of their most lavish display, 

 the temperature varies from 77° to 83° ; at Tahiti from 77° to 

 80°, and about the same at the large groups to the west of it. 

 At the Hawaiian Islands, lying between 19° and 22° north 

 latitude, it is as high sometimes as 81°. 



In our own hemisphere, among the Antilles, Bahamas, and 

 along the southern coast of Florida, I have found the tem- 

 perature of the water near the shore, at different seasons, from 

 78° to 82°, and in all these regions coral reefs abound. 



