X GEOLOGICAL REFORM 827 



of which a record is preserved in stratified 

 deposits. 



The accusation that we have been running 

 counter to the princiiolcs of natural philosophy, 

 therefore, is devoid of foundation. The only 

 question which can arise is whether we have, or 

 have not, been tacitly making assumptions which 

 are in opposition to certain conclusions which 

 may be drawn from those principles. And this 

 question subdivides itself into two : — the first, 

 are we really contravening such conclusions ? the 

 second, if we are, are those conclusions so firmly 

 based that we may not contravene them ? I reply 

 in the negative to both these questions, and I 

 will give you my reasons for so doing. Sir 

 Wilham Thomson believes that he is able to 

 prove, by physical reasonings, " that the existing 

 state of things on the earth, life on the earth — all 

 geological history showing continuity of life 

 — must be limited within some such jDcriod 

 of time as one hundred million years " {Ice. 

 cit. p. 25). 



The first inquiry which arises plainly is, has it 

 ever been denied that this period inay be enough 

 for the purposes of geology ? 



The discussion of this question is greatly 

 embarrassed by the vagueness with which the 

 assumed limit is, I will not say defined, but 

 indicated, — " some such period of past time as 

 one hundred million years." Now does this mean 



