78 ZOOLOGICAL GEOGRAPHY. [part hi. 



there is good reason to believe that many species have become 

 extinct since the European occupation of them. When small 

 islands are much cultivated, many of these molluscs which can 

 only live under the shade of forests, are soon extirpated. In 

 St, Croix many species have become extinct at a comparatively 

 recent period, from the burning of forests ; and as we know that 

 in all the islands many of the species are excessively local, being 

 often confined to single valleys or ridges, we may be sure that 

 wherever the native forests have disappeared before the hand of 

 man, numbers of land-shells have disappeared with them. As 

 some of the smaller islands have been almost denuded of their 

 wood, and in the larger ones extensive tracts have been cleared 

 for sugar cultivation, a very considerable number of species have 

 almost certainly been exterminated. 



General Conclusions as to tlie Past History of tlie West Indian 

 Islands. — The preceding sketch of the peculiarities of the animal 

 life of these islands, enables us to state, that it represents the 

 remains of an ancient fauna of decided Neotropical type, having 

 on the whole most resemblance to that which now inhabits the 

 Mexican sub-region. The number of peculiar genera in all 

 classes of animals is so great in proportion to those in common 

 with the adjacent mainland, as to lead us to conclude that, 

 subsequent to the original separation from the Mexican area, a 

 very large tract of land existed, calculated to support a rich and 

 varied fauna, and, by the interaction of competing types, give 

 rise to peculiar and specially modified organisms. We have 

 already shown that the outline of the present islands and the 

 depths of the suiTOunding seas, give indications of the position 

 and extent of this ancient land ; which not improbably occupied 

 the space enclosed by uniting Western Cuba with Yucatan, and 

 Jamaica with the Mosquito Coast. This land must have 

 stretched eastward to include Anguilla, and probably northward 

 to include the whole of the Bahamas. At one time it perhaps 

 extended southward so as to unite Hayti with northern 

 Venezuela, while Panama and Costa Rica were sunk beneath the 

 Pacific. At this time the Lesser Antilles had no existence. 



The only large island of whose geology we have any detailed 



