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 their existence as a coral reef dates 
from the time of the closing of the passages through 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 origin 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. 
