CONTINUITY OF PROCESS 173 



As it is now, so must it have been in past time. 

 Hutton and Playfair pointed to the stratified rocks 

 of the earth's crust as demonstrations that the same 

 processes which are at work to-day have been in oper- 

 ation from a remote antiquity. By thus placing their 

 theory on a basis of actual observation, and providing 

 in the study of existing operations a guide to the 

 interpretation of those in past times, they rescued 

 the investigation of the history of the earth from the 

 speculations of theologians and cosmologists, and 

 established a place for it among the recognised induc- 

 tive sciences. To the guiding influence of their philo- 

 sophical system the prodigious strides made by modern 

 geology are in large measure to be attributed. And 

 here in their own city, after the lapse of a hundred 

 years, let us offer to their memory the grateful homage 

 of all who have profited by their labours. 



But while we recognise with admiration the far- 

 reaching influence of the doctrine of uniformity of 

 causation in the investigation of the history of the 

 earth, we must upon reflection admit that the doctrine 

 has been pushed to an extreme perhaps not contem- 

 plated by its original founders. To take the existing 

 conditions of Nature as a platform of actual knowledge 

 from which to start in an inquiry into former con- 

 ditions was logical and prudent. Obviously, however, 

 human experience, in the few centuries during which 

 attention has been turned to such subjects, has been 

 too brief to warrant any dogmatic assumption that 

 the various natural processes must have been carried 

 on in the past with the same energy and at the same 

 rate as they are carried on now. Variations in energy 



