ARVICOLA AMPHIBIA. 203 



clition of limestone caves as the cause of their introduction, 

 viz., that of being traversed by small rivers, which in some 

 limestone countries lose themselves in cavities, and after 

 running through a series of subterranean caverns, reappear 

 on the surface at a distance from the spot where they first 

 disappeared. A change in the relative levels and other 

 physical features of a country, and a variety of other modi- 

 fying circumstances, might afterwards alter the relation of 

 a cavern to such subterraneous stream. 



Dr. Buckland, however, is disposed to refer the intro- 

 duction of the smaller Mammalia, as well as the larger 

 ones, to the agency of the hyaenas. He says,* " The ex- 

 treme abundance of the teeth of Water-rats has also been 

 alluded to ; and though the idea of hyaenas eating rats 

 may appear ridiculous, it is consistent with the omnivorous 

 appetite of modern hyaenas, and with the fact, quoted by 

 Johnson, that they feed on small animals, as well as car- 

 rion and bones ; nor is the disproportion in size of the 

 animal to that of its prey greater than that of wolves 

 and foxes, which are supposed by Captain Parry to feed 

 chiefly on mice, during the long winters of Melville Island. 

 Hearne, in his ' Journey to the Northern Ocean, 1 mentions 

 the fact ' of a hill, called Grizzly Bear Hill, being deeply 

 furrowed and turned over like ploughed land, by bears in 

 search of ground squirrels, and perhaps mice, which con- 

 stitute a favourite part of their food. 1 If bears eat mice, 

 why should not hyaenas eat rats ? Our largest dogs eat 

 rats and mice ; jackalls occasionally prey on mice, and 

 dogs and foxes will eat frogs. It is probable, therefore, 

 that neither the size nor aquatic habit of the Water-rat 

 would secure it from the hyaenas. They might occasion- 

 ally, also, have eaten mice, weasels, rabbits, foxes, and 



* Reliquiae Diluviana;, p. 33. 



