118 THREE CRUISES OF THE " BLAKE." 



echinoderms, all indicate the source from which they have been 

 derived. 



It is interesting in connection with the currents to note that, 

 as far as we know, the Bermudas were never inhabited by Caribs 

 or North American Indians, their great distance from land and 

 the facility with which boats, carried northward by the Gulf 

 Stream, must have drifted towards the mainland rendering such 

 an immigration quite improbable. 



In this special case it is not difficult to go back to the time 

 (and that in a comparatively recent geological period) when the 

 Gulf Stream did not run its present course, and when probably 

 also the Bermudas, if they existed at all, were merely the nu- 

 cleus on which the subsequently formed atoll has been raised. 

 We may safely assert that then* existence as a coral reef dates 

 from the time of the closing of the passages thi'ough which the 

 equatorial currents flowed across the Isthmus of Tehuantepec 

 and the other passes of the Isthmus of Panama. The coral reef 

 of the Bermudas is probably, therefore, of very much more re- 

 cent orio'in than the reefs on the windward sides of the West 

 India Islands, the southern coast of Cuba, the Mosquito coast, 

 the Yucatan Bank, the north shore of Cuba, the Florida reefs, 

 and the Bahamas and their connecting islands. It is to these 

 older reefs that the more recent Bermuda reefs owe their ori- 

 gin. The embryos of the corals were floated northward by the 

 Gulf Stream, and finding suitable conditions of temperature, as 

 well as of depth, due to this very current, became attached, and 

 soon formed a gigantic atoll rivalling in size some of the more 

 prominent atolls of the Pacific. Thus we readily account for 

 the presence of coral reefs off the Atlantic coast of North 

 America, in latitudes which are rather more northerly than the 

 usual extension of coral reefs in other seas. The same causes 

 which have thus scattered as far north as the Bermudas the 

 fauna and flora of the West Indies, and of some parts of tro- 

 pical South America, have also been influential in extending 

 some of these types to their more distant habitats, such as the 

 Azores, the Canary Islands, Cape Verde Islands, Madeira, the 

 west coast of tropical Africa, as well as to other points on the 

 east coast of North America, where a few of the same animals 

 and plants occur. 



