192 HUTTONIAN THEORY 



detect them on the way, and we feel constrained to 

 believe that their march must be excessively slow. 



There is no reason to think that the rate of organic 

 evolution has ever seriously varied; at least no proof 

 has been adduced of such variation. Taken in con- 

 nection with the testimony of the sedimentary rocks, 

 the inferences deducible from fossils entirely bear out 

 the opinion that the building up of the stratified crust 

 of the earth has been extremely gradual. If the many 

 thousands of years which have elapsed since the Ice- 

 Age have produced no appreciable modification ot 

 surviving plants and animals, how vast a period must 

 have been required for that marvellous scheme of 

 organic development which is chronicled in the rocks ! 



After careful reflection on the subject, I affirm that 

 the geological record furnishes a mass of evidence 

 which no arguments drawn from other departments 

 of Nature can explain away, and which, it seems to 

 me, cannot be satisfactorily interpreted save with an 

 allowance of time much beyond the narrow limits which 

 recent physical speculation would concede. 1 



I have reserved for final consideration a branch of 

 the history of the earth which, while it has become, 

 within the lifetime of the present generation, one of 

 the most interesting and fascinating departments of 

 geological inquiry, owed its first impulse to the far- 

 seeing intellects of Hutton and Playfair. With the 

 penetration of genius these illustrious teachers per- 

 ceived that if the broad masses of land and the great 

 chains of mountains owe their origin to stupendous 



1 The problem of Geological Time was made the subject of a 

 later address. See postea, p. 198. 



