68 W J MCGEE — UNIFORMITARIANISM AND DEFORMATION. 



figments of budding scientific imagination were substituted for facts of 

 observation. The two primitive hypotheses have much in common, yet 

 they are unlike in an important particular — one has been abandoned so 

 completely that it ma}^ be questioned w^hether the pendulum of opinion 

 has not swung back too far; the other is retained today, perhaps justly 

 in its limited application to orogeny but certainly in violence to the 

 facts of epeirogeny, by many geologists. 



There was reason for the early abandonment of the fracture theory of 

 valleys : It is an easy step from the perception of channel-cutting to the 

 recognition of valley-carving, and another easy step to the homologic in- 

 ference that the hill and dale of the countryside were fashioned by the 

 beating rain and the flowing rill; the agency is tangible and visible; 

 the process though variable in rate is constant in kind and in action ; , 

 there is no occasion to break the chain of direct homology in process by 

 appealing to the analogy of unlike things. The abandonment of the 

 hypothesis, or, rather, the substitution of more exact observation and 

 advanced reasoning, marked an important epoch in the development of 

 geology, yet the advance was natural, and would have been made ere this 

 even if the light of Lyell's genius had not burned. 



The long retention of the contractional hypothesis of deformation is 

 not surprising : the oscillations of the earthcrust are slow, in most cases 

 hardly to be detected without refined surveys. In many cases they are 

 confined to local shores, where they are obscured by tides, wave-action, 

 and the beating of storms. The surveys by which they are detected are 

 commonly made by men trained in abstract concepts to the extent that 

 they have no living sense of terrestrial activity and either ignore or deny 

 the movement their measurements attest; there is no tangible, visible 

 agency like the ever-active river to attract attention and stimulate imagi- 

 nation ; there is little in the actual movement of the earthcrust for 

 observation to seize, and until observations have accumulated, no clearly 

 defined facts for homologic inference to grasp. Moreover, it is an easy 

 step in analogic reasoning from the buckled beam, wrinkled roof-plate 

 and crumpled model to the flexed and thrust-faulted stratum, an easy 

 analogic step from the shriveled apple to an hypothetic corrugated planet; 

 there may indeed be nothing, probably there is nothing, in common 

 between the miniature wrinkling of the model in the laboratory and the 

 grand deformation of a great planet, yet no chasm is too broad for the 

 bridge of analogic inference. There is nevertheless little real reason for 

 the persistence of the hypothesis, since it is without basis in direct homo- 

 logic inference ; no human eyes have seen horizontal earth movements, 

 save possibly as a subordinate element in the vertical movement, and at 



