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THE UNIVERSE. 



the great surprise of travellers, become extinguished on 

 their obscure journey before they reach the bottom. 



Other cavities of only very small extent attract the 

 attention of naturalists much more than those of which 

 we have spoken. These are the bone-caves, in which we 

 find heaps of bones of carnivora, principally bears and 

 hyenas, which lived at an epoch very near our own, and 



314. Dead Sea in the 3Iammotli Cave. 



the numbers of which in such places we cannot very well 

 explain. It is, however, probable that they were brought 

 thither by currents of water. Sometimes, too, we find mixed 

 with them traces of the handicraft of the most ancient 

 human races, and sometimes human crania. 



But the difficulties presented by the exploration of 

 grottoes and mines, the desert nature of the country where 

 their mouths open, and the ignorance of the rude inhabi- 



