GEOLOGY IK SERVICE OF MAN WATTS 287 



is continually haunted by the feeling that the author was struggling 

 for a single missing generalization which he failed to find; and 

 although, in almost every branch of the subject treated, Lyell leads 

 up again and again to the missing conception, and though the facts 

 and inferences Avhich he marshalled can now be seen to be marching 

 on this great idea, he never quite succeeded in attaining it for him- 

 self. It was left for Darwin, than whom no one was more conscious 

 of what he owed to Lyell, to see that the facts must rest on some great 

 single fundamental principle, to realize that this principle was evolu- 

 tion, and to apply it to his own branch, the development of life. 



Lyell had proved that the long history of the earth as recorded 

 in the rocks revealed the operation of causes, small in relation to 

 the earth as a Avhole, but persistent, the majority of them still in 

 action. It was a further debt to Lyell that Darwin should bring in 

 the continuous operation of small causes as the machinery operating 

 and guiding the evolution of life. 



But though the work of geologists, as summed up by Lyell, pro- 

 vided the starting point for the conception of organic evolution, it 

 did not stop here. The idea of Uniformitarianism in which that 

 work culminated was meant as a reaction against the fantastic opera- 

 tions postulated by the Catastrophists, and was never intended to 

 imply that these causes in the past were always balanced or distrib- 

 uted as they are now. There was in Lyell's statements nothing to 

 indicate that denudation or earth movement might not have been 

 more active at periods of the past, that organic change might not 

 accelerate or slow down, that there might not be variations in the 

 trends of continental or oceanic development resulting in climatal 

 and other changes, or that the very sources and intensities of energy 

 from outside or inside the earth might not seriously vary. Only, 

 warrant must be found for all such suppositions with regard to the 

 earth of the past from fuller study of the earth of the present. And 

 if we recognize the inner spirit which inspired the eloquent words 

 of Lyell, when he had grasped that Darwin had supplied the one 

 missing idea, we can not fail to see that his Uniformitarianism in- 

 cluded evolution as one of the "existing causes" to be taken into 

 consideration. 



The physiology of the earth, however, is that of a very complex 

 organism, and we are sure that we do not yet know all the forces 

 internal and external acting upon it, still less their relative value and 

 intensity, their distribution and variation in the past, or the precise 

 records which each is capable of imprinting on the rocks of the earth- 

 crust. But it is becoming clearer that there has been a periodicity in 

 the stages of development of the earth crust, and that on these great 

 pulses of earth life there have been imposed innumerable Avaves of 



