8 JONES ON NATURAL HISTORY OF THE BERTklUDAg. 



in the Atlantic at whicli the reef bnikliiig polyps raise their 

 structures. Dana, in his valuable work on coral reefs and 

 islands, has shewn that the growth of coral reefs depends 

 particularly on the temperature of the ocean, the character 

 of coasts as regards depth of water, nature of the shores, 

 presence of streams, and other conditions, especially liability 

 of exposure to destructive agents. 



Now, the Bermudas lying as they do on the outer or eastern 

 edge of the Gulf Stream, are laved by its waters highly charged 

 with animal life brought from the Caribbean Sea ; and, as it is 

 to the eastern edge of the stream that all drift matter inclines, 

 so do the Bermudas gain no ordinary share of foreign forms, 

 which are rarely, if ever, observed on the adjacent coast, even 

 -at a much lower latitude. These islands also, protected as they 

 are from the influence of colder northerly currents by the vast 

 body of heated water which flows past, present a fruitful field 

 for marine organisms requiring an almost tropical heat for their 

 perfect development; and thus it is that we find the reef build- 

 ing corals growing so well in an extreme northern latitude, 

 where the temperature of the air during the mouths of January 

 and February, sometimes falls as low as twenty degrees below 

 the temperature of the ocean required for the growth of reef 

 building corals. 



This question regarding the proper temperature required for 

 the development of reef corals, is still open for determination, 

 for although 64° is named as the probable mean temperature of 

 the seas in which such corals grow, it is by no means improbable 

 that the shallow tidal pools, situate between tidal marks, on the 

 shores of the Bermudas, which generally contain corals of the 

 same species as those on the reefs, have the water the}' contain 

 of a much lower temperature when cold northerly winds are 

 blowing for two or three days in succession ; reducing the air 

 temperature- so low that frost occasionally occurs, although very 

 rarely, and ice has been observed the thickness of half a crown. 

 It is also generally supposed that corals of the genera Asfrcea and 

 Moeandrina grow better in the warmest waters ; but on the Ber- 

 muda reefs members of these genera are met with of an amazing 

 size, especially the well known " brainstonc " (Mcvnjidn'na cere- 



