FOSSIL MAMMALIA. 19 



posit where they are found. The first supposition, then, 

 which, as we observed, the Professor adopted in explanation of 

 the phenomena of Kirkdale-cave, is the only one that can be 

 admitted in reference to all the rest which exhibit pheno- 

 mena precisely similar. There are certainly some cases of 

 caverns in which we may otherwise account for the presence of 

 bones. Animals may have retired there to die, fallen acci- 

 dentally into their fissures, or been washed in by diluvial 

 waters. But such hypotheses will only explain the cases 

 where the bones are few and not gnawed, the caverns large, 

 and their fissures extending upwards. In all other instances 

 we can only account for the vast accumulation of bones by the 

 agency of beasts of prey. 



It is^ however, quite certain that the period in which the 

 animals lived in these caves was considerably subsequent, not 

 only to the formation of the extended rocky strata of which 

 the mountains where they are excavated are composed^ but to 

 that of similar strata of more recent date. No permanent 

 inundation penetrated into these subterraneous recesses, or 

 formed there any regular stony deposition. The rolled peb- 

 bles that are found there, and any traces of detrition on the 

 bones, indicate nothing but the transitory passage of evanes- 

 cent waters. 



*' How, then," exclaims the Baron, " have the ferocious 

 beings which once peopled our ancient forests, been extirpated 

 from the surface of the earth ? T he only reply that can be 

 given is, that they were destroyed at the same time, and by 

 the same agency, as the large herbivora, which were fellow- 

 inhabitants with themselves, and of which no traces in existing 

 nature are any longer to be found."" 



The debris of birds have been found in the fossil state, the 

 genera of which involve some difiiculty in the determination. 

 Of these we treat in the proper place. 



The genera of fossil reptiles are well characterized ; such 

 are the tortoises, the crocodiles or saurians, the monitors, the 



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