22 CRUISE OF THE BARRERA 



appellation is not inept, for, like limestone moun- 

 tains the world over, they have been carved by 

 atmospheric agency into all manner of fantastic 

 shapes and often present from a distance this 

 organ-pipe appearance. They are always very 

 steep, often displaying vertical walls {paredones) 

 of quite one thousand feet elevation. They are 

 densely overgrown, wherever vegetation can find 

 lodgment, with a very characteristic flora, and 

 harbor a rich and varied fauna both altogether 

 different from that of the lomas or of the lower 

 plains. It is upon the sierras, that Cuba's astonish- 

 ing wealth of moUuscan life exists. As these land 

 mollusks cannot maintain themselves away from 

 the limestone of the sierras, their restricted little 

 world may be said to consist of the ''continental 

 area" of the sierras and the ''islands" represented 

 by the mogotes. From whatever source was 

 derived this extraordinary aggregation of land 

 shells with its many unique species and genera, it is 

 reasonably certain that it developed to its climax 

 only since the elevation of these sierras. Since 

 this elevation, the forces of demolition have been 

 actively at work, and their original range of habitat 

 has continually dwindled in area. Their "conti- 



