( 322 ) [July.. 



III. THE EATE OF GEOLOGICAL CHANGE. 



By H. M. Jenkins, F.G.S., Secretary of the Eoyal Agricultural 



Society of England. 



Public opinion on questions of theoretical geology grows slowly, 

 and usually precedes the statement of important speculations. 

 The progress of discovery leads up to the induction, which, after 

 floating more or less hazily in the minds of geologists for a certain 

 time, is at last enunciated piecemeal at irregular intervals by the 

 more daring theorists. Finally the scattered fragments are col- 

 lected and arranged, bound together by the idea which connects 

 them, and placed on record as a complete whole. This last is the 

 task which I propose to attempt in reference to the progress of 

 public opinion on the subject at the head of this article. 



But first, let me clear the way by a short summary of the ideas 

 which prevail amongst English geologists, so far as they bear on 

 this subject. The prominent feature of the favourite modern school 

 of geology in England — Uniformitarianism — is the belief that the 

 forces in operation at the surface of the earth in former times dif- 

 fered in no appreciable degree from those now in action. This 

 article of faith is, however, commonly restricted to what, for con- 

 venience of expression, has been termed " Geological time " — a 

 period which is entirely represented by the rocks found on the 

 earth's surface, from the oldest to those now in course of formation. 

 According to this school, the rate of geological change has been 

 approximately equal throughout the vast period which has elapsed 

 since the deposition of the oldest stratified rock. Local variations 

 of this law would doubtless be admitted by even the most thorough 

 advocate of LTniformity, but the broad general principle character- 

 istic of the creed is equality in the rate of change throughout all 

 geological time. 



Catastrophism, which is the name usually given to the other 

 great school of geologists, is distinguished broadly by the tenet 

 that in past times the forces in operation at the surface of the 

 globe were of far greater intensity than they are now, and that 

 great physical changes were then produced by more or less violent 

 cataclysms. Probably there are geologists who now-a-days reject 

 the catastrophes, but still cling to the belief that modern forces are 

 much less intense, and modern changes much less rapid and ex- 

 tensive, than those which occurred in former geological periods. 

 Therefore, whichever view we take of this theory, it is clear that 

 its advocates believe that the rate of geological change was greater 

 in past times than it is now ; and the inference appears fair that, 

 according to this school, the rate of change has, on the whole, pro- 

 gressively diminished from the earliest down to modern times. 



