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ledge is the power of exposing the fallacy of that 

 which is merely assumed. 



In the case of geology this power must rest mainly 

 on the nature of the evidence which the science can 

 adduce, and this evidence, though inferential in its 

 character, is, when based upon well-observed facts, as 

 certain and reliable as anything connected with human 

 testimony can be. We find, for example, in certain 

 caverns, the bones of various animals imbedded in the 

 calcareous earth that has accumulated on the floors. 

 On breaking up this stalagmitic crust we discover that 

 many of the bones have been gnawed, and that some, 

 and especially the hollow ones, have been split up into 

 longitudinal splinters. We ascribe the gnawing to 

 den-frequenting carnivorous animals like the hysena, 

 and the splitting to human instrumentality, as we 

 know of no other creature save man capable of so 

 manipulating. These inferences are of themselves 

 sound and reliable ; but they amount to absolute 

 certainty when on further examination we discover 

 the hardened and peculiar excrement of the hysena, 

 and the stone hatchet of the rude marrow-sucking 

 savage. Supposing that no implements had been 

 found, and that doubts existed as to the splitting of 

 the bones, we find on still further research ashes and 

 fragments of wood-charcoal scattered through the 

 stalagmite, and then the presence of man in these 



