ON THE GEOLOGY OF JUKBADOS. 241 



His words on this subject arc not so clear as could be wished. 

 The Tertiary deposits of Panama belong to a period of jj:reater 

 depression, and this is not likely to have been contemporaneous with 

 an elevation of the Caribbean region, especially as similar Tertiarj' 

 deposits occur in that region. On a previous page ho states that 

 such an elevation (*. e. of SOU fathoms) would almost unite Jamaica 

 to Honduras and Nicaragua ; a fortiori, Nicaragua and Panama 

 would have been 3000 feet higher than they are now. Finally, he 

 admits that the geographical conditions which he indicates may 

 never have existed. We certainly think they never did : there 

 may have been a time when the coast-line of the whole region 

 coincided approximately with the 500-fathom line, but we do not 

 believe that depression in Central America coincided with elevation 

 in the Antilles. 



We think that biologists require to be cautioned against assum- 

 ing the former connexion of islands with continents on the basis of 

 hydrographic evidence, unless it is supported by geological evidence 

 of subsidence, for it is obvious that the shallowness of an inter- 

 vening sea may be due to recent elevation. In the case of the 

 Antilles, there is no evidence for the idea that the ridge on which 

 the islands stand has been land in Pleistocene time, nor is the 

 present distribution of animals on the islands such as to suggest a 

 continental connexion of later date than the Miocene period. There 

 is nothing clearer in the geological history of the West Indies, so 

 far as it is at present known, than the fact that a great depression 

 began in a mid-Tertiary or Miocene period, and continued through 

 Pliocene times, and that this was succeeded by a movement of 

 upheaval, which lasted down to very recent times. 



We think that the shallowness of the sea between so many of 

 the islands, and between Florida and the Bahamas, is due to recent 

 upheaval, and that before this movement commenced there was 

 no connexion between the two Americas, the intermediate Antillean 

 region being an archipelago of islands separated by deep channels 

 and waterspaces. 



The limited terrestrial fauna of the West-Indian Islands, and 

 the occurrence of certain genera which may be regarded as ancient 

 types, confirm the geological evidence for the long-continued isola- 

 tion of the Antillean area. The peculiarities of the fauna and 

 flora of Central America are also capable of explanation on the 

 hypothesis that the higher parts of that area were, until a recent 

 period, part of the isolated Antillean archipelago, and washed by a 

 current which set in from the east. 



Moreover, the relations of the modern marine Caribbean fauna to 

 that of the Pacific are in entire accord with our belief that the separa- 

 tion of the two regions is of very recent date. The following obser- 

 vations of Prof. Alex. Agassiz are interesting in this connexion * : — 

 " The resemblance of the fauna of the Gulf of Mexico and of the 

 Caribbean to that of the Pacific was noticed by writers, even at a 



* ''Three Cruises of the ' Biiike.'"' Bull. Harvard Mus. vol. xir. (1888) 

 p. laT. 



