NATURAL HISTORY NINETEENTH CENTURY. 649 



FIG. 322. BONE CAVERN. 



geologist. Science has gained by the many voyages in high latitudes 

 which have taken place in the present century, and in the gallant 

 attempts to reach the Pole itself which have been made in her interest 

 Many bones of extinct species of mammalia have been met with 

 in caves, and have received much attention from naturalists since 

 Cuvier's time. These caverns, a typical section of which is shown 

 in Fig. 322, generally occur in limestone rocks, and though the en- 

 trance is usually very narrow, they have been found to contain enor- 

 mous quantities of bones of various animals, and in several cases 

 traces of the human species, with whom these animals appear to have 

 been contemporaneous. Some of these traces consist of the now 



