GEOLOGICAL CHANGE, AND TIME. 129 



new s])ecies. We imist admit that such trausitious have occurred, that 

 indeed they liave been in proj^ress ever since organized existence began 

 upon our phmet, and arc doubtless talving phice now. But m'c can not 

 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 va- 

 riation. Taken in connection 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 ex- 

 tremely gradual. If the many thousands of years which have elapsed 

 since the Ice age have produced no appreciable modification of sur- 

 viving 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, can not l)e satisfactorily interpreted save with an allowance of time 

 much beyond the narrow limits which recent physical speculation would 

 concede. 



1 have reserved for hnal 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. \^"ith the i)enetration of genius these illustrious 

 teachers perceived that if the broad nuisses of land and the great 

 chains of mountains owe their origin to stupendous movements which 

 from time to time have convulsed the earth, their details of contour 

 nuist be mainly due to the eroding power of running water. They 

 recognized tluit as the surface of the land is continually worn down, it 

 is essentially by a [)r<)cess of scnl[)tnre that the physiognomy of exery 

 country has l)een develoi)ed, valleys being hollowed out and hills left 

 standing, and that these ineipmlities in topographical detail are only 

 varying and local accidents in the progress of the one great i)rocess of 

 the degredation of tlie land. 



From the broad and guiding outlines of theory tlius sketched we 

 have now advan(;ed amid ever-widening multiplicity of detail into a 

 fuller and nobler (conception of the oi'igin of scenery. The law of evo- 

 lution is written as legibly on the landscapes of the earth as on any 

 other page of the book o£ nature. Not only do we recognize that the 

 existing toi)ograi)hy of the continents, instead of being primeval in 

 origin, has gradually been developed aftei' many precedent mutations, 

 but we are enabled to trace these earlier revolutions in tlie structure 

 of every hill and glen. Each mountain chain is thus found to be a 

 II. Mis. 114 



