EVIDENCES OF PAST AGES. 87 



existence in Barbados therefore, suggests the idea that 

 it was formed in a deep basin which was open to the 

 Pacific as Well as to the Atlantic, and consequently at a 

 time when the Isthmus of Panama did not exist." 



What, therefore, passed through my mind, as we 

 gathered up a large bagful of these Swan Island deposits, 

 taken from a boring, was this : would they be found on 

 microscopical examination to contain some of these 

 foraminiferal or radiolarian organisms which had lived 

 ages ago, and whose skeletons had sunk to form an ooze 

 at the bottom of this division of the Caribbean, at 

 a time when there was no land connection between 

 North and South America, and when, therefore, this 

 part of the sea-bottom was overflowed by waters from 

 the Pacific ? 



On the other hand, the deposit might consist of some 

 fine volcanic dust , which was not very likely ; or it might 

 be a residual deposit left after the decomposition of a 

 limestone, formed on the sea-bottom, out of the dead 

 remains of coral organisms or other marine animals, 

 living either upon or near the bottom, which when they 

 die leave their calcareous frameworks to form vast 

 deposits, the limestone rocks of future ages. 



What made the first alternative a possibility, or even 

 a probability, was the fact, to which we referred in 

 Chapter VI., that we had found among the coral reefs sur- 

 rounding the island some small fish which previously had 

 never been found anywhere else but on the Pacific coast 

 of the American continent ; which fish we may regard as 

 having been cut off from their colleagues of the Pacific 

 when Central America finally emerged from the bottom 

 of the sea. 



Dr. Andrews, F.R.S., and Mr. Mukler, of the British 

 Museum, have very kindly examined the deposits for me, 

 and found in it the following genera of Foraminifera: 

 Ammodiscus, Cristellaria, Glohigerina, Lagena, Nodosaria, 

 Orhulina, Polymorphina, Rotalia and Sphceroidina. There 

 were also some slight traces of diatoms and sponge spicules 



