i 7 4 HUTTONIAN THEORY 



might have been legitimately conceded as possible, 

 though not to be allowed without reasonable proof 

 in their favour. It was right to refuse to admit the 

 operation of speculative causes of change when the 

 phenonema were capable of natural and adequate 

 explanation by reference to causes that can be watched 

 and investigated. But it was an error to take for 

 granted that no other kind of process or influence, 

 nor any variation in the rate of activity save those 

 of which man has had actual cognisance, has played 

 a part in the terrestrial economy. The uniformitarian 

 writers laid themselves open to the charge of main- 

 taining a kind of perpetual motion in the machinery 

 of Nature. They could find in the records of the 

 earth's history no evidence of a beginning, no prospect 

 of an end. They saw that many successive renovations 

 and destructions had been effected on the earth's 

 surface, and that this long line of vicissitudes formed 

 a series of which the earliest were lost in antiquity, 

 while the latest were still in progress towards an appar- 

 ently illimitable future. 



The discoveries of William Smith, had they been 

 adequately understood, would have been seen to offer 

 a corrective to this rigidly uniformitarian conception, 

 for they revealed that the crust of the earth contains 

 the long record of an unmistakable order of progres- 

 sion in organic types. They proved that plants and 

 animals have varied widely in successive periods of the 

 earth's history, the present condition of organic life 

 being only the latest phase of a long preceding series, 

 each stage of which recedes further from the existing 

 aspect of things as we trace it backward into the past. 



