from the Observations of himself and Mr. Clemson. 29 



bearing his shell to denote the character and extent of his 

 wanderings, they proceed for miles into the interior. Thus, 

 at the distance of eight or ten miles from the nearest shore, 

 we trace them to the very summit of a precipitous mountain, 

 almost twelve hundred feet high. When these borrowed ha- 

 bitations become too confined for the accommodation of their 

 tenants, the crabs desert them, and seek for larger shells, 

 leaving the others mingled with the terrestrial shells, as we 

 observed. The marine shells which had been thus convey ed 

 from the sea to the top of La Silla were 

 Trochus, two or three species. 



Turbo, two or three species, particularly T. muricatus, Lam. 

 Littorina, one. 

 Monodonta, one. 

 No doubt other genera and species were also transported 

 thither by the same agents, but those above mentioned we can 

 testify to. 



Of the land shells, which exist equally in a fossil state on 

 the mountain of La Silla, and were seen abundantly in their 

 living state in the same locality, we have collected the follow- 

 ing, of which Mr. Isaac Lea has kindly furnished us with the 

 specific names. 



Cyclostoma sulcata, var Lamarck. 



Itupa mumia Lam. 



Carocolla marginata Lam. 



Carocolla ? 



Helix microstoma Lam. 



Helicogena auricoma 



Helix muscarum Lea. 



Helix purpuragula ? Lea. 



Clausilia ? 



Caves of La Silla. — At about a hundred and fifty feet below 

 the summit of the mountain of this name is an extensive suite 

 of caves. Those we passed through, six in number, extended 

 above three hundred feet to the south, and others stretch oft" 

 to the north, in the compact white limestone to which we have 

 referred. These caves swarmed with bats, snails, spiders, 

 tarantulas, scorpions, and other vermin, and the large snake 

 called the Majus. They are also the resort of hogs, which run 

 wild in the woods, and bring hither a well-known pest in the 

 insect termed the Jigger. 



The entrance to the cave is at the bottom of a perpendicu<- 

 lar cliff of limestone. The interior is not unlike to an Anglo- 

 Norman crypt, having a heavy groined roof and 'pillars of 

 continually increasing stalactite. This tendency to encrust 

 the walls or sides contracts the areas of the chambers, to some 



