GROWTH OF GEOLOGY. 227 



. . . that is not the same thing as proving that they 

 did so produce them." ^ Such proof can only he 

 afforded by a detailed study of the strata, more ex- 

 tensive and intensive, than even now exists. 



But as this detailed study has proceeded, it has 

 become more and more clear not only that the earth 

 has evolved from a very different primitive state to 

 its present form, but furthermore that through the 

 immense expanse of its history there have been nota- 

 ble changes in the earth-sculpturing factors. The 

 indisputable proof of great Ice-Ages and of enormous 

 thrust-movements may serve to show that uniformi- 

 tarianism recoiled too far from catastrophism. To 

 try to explain the phenomena of glaciation without 

 glaciers strained the uniformitarian theory to the 

 breaking-point. 



Evolutionary. — The cataclysmal geology was un- 

 scientific, for it invoked the aid of undemonstrable 

 factors ; the uniformitarian geology was inconsistent, 

 for while it sought to interpret the past in terms of 

 the present, it rejected the evolution idea which sums 

 up the whole history as a process of becoming; the 

 modern evolutionary geology has inherited the 

 strength of the uniformitarian school and has given 

 this fresh virility by recognising that the history of 

 the earth is a natural development in which at every 

 stage the present is the child of the past and the par- 

 ent of the future. The evolutionist school differs 

 from the uniformitarian, (a) in admitting in its full- 

 est sense the hypothesis that the earth has had a 

 natural history from a nebular or molten mass down 

 to the twentieth century, and {h) in admitting the 

 likelihood that in the course of the evolution there 



* J. E. Marr, Address Section C, Rep. Brit. Ass., 1896. 



