186 ALEXANDER AGASSIZ 



been interested in the study of this chief cause of the 

 great difference in the climate of the eastern United 

 States and western Europe. 



From such soundings as were already known, his 

 own and those subsequently made by Captain Bartlett, 

 Ag-assiz concluded that at one time the Caribbean was 

 most probably virtually an arm of the Pacific, or at all 

 events was more closely connected with it than with the 

 Atlantic. This furnishes a ready explanation of the 

 fact that the fauna and flora of the West Indies bear a 

 closer relation to Central and South America than to the 

 southern part of the United States. This view also ex- 

 plains the close similarity of the littoral fauna on both 

 sides of the Isthmus of Panama. The theory was further 

 strengthened by Agassiz's discovery, on subsequent ex- 

 peditions, that the deep-sea forms on each side of the 

 Isthmus bore a closer relation to each other than did 

 those of the Caribbean Sea to the deep-sea fauna of the 

 Atlantic. 



These expeditions also threw much light on the geo- 

 graphical distribution of marine fauna, and the question 

 of the survival of archaic types in the depths of the 

 ocean. Writing of these matters Agassiz says : — 



" The depths of the seas seem at first glance the 

 safest of all retreats, — the secret abysses where the 

 survivors of former geological periods would be sure to 

 be found. Yet oceanic dredgings have not brought to 

 light as many of the ancient types as the more enthus- 

 iastic dredgers had led us to expect. They have, how- 

 ever, given us a large number of animals living in deep 

 water, where they have been subjected to no violent 

 changes, to which no revolutions of the surface of the 



