TWO ANTAGONIST DOCTRINES OF GEOLOGY. 669 



have operated; and we are in danger of errour, if 

 we seek for slow and shun violent agencies further 

 than the facts naturally direct us, no less than if we 

 were parsimonious of time and prodigal of violence. 

 Time, inexhaustible and ever accumulating his effi- 

 cacy, can undoubtedly do much for the theorist in 

 geology; but force, whose limits we cannot mea- 

 sure, and whose nature we cannot fathom, is also a 

 power never to be slighted : and to call in the one 

 to protect us from the other, is equally presump- 

 tuous, to whichever of the two our superstition 

 leans. To invoke Time, with ten thousand earth- 

 quakes, to overturn and set on edge a mountain- 

 chain, should the phenomena indicate the change to 

 have been sudden and not successive, would be ill 

 excused by pleading the obligation of first appealing 

 to known causes (KA). 



In truth, we know causes only by their effects ; 

 and in order to learn the nature of the causes which 

 modify the earth, we must study them through all 

 ages of their action, and not select arbitrarily the 

 period in which we live as the standard for all 

 other epochs. The forces which have produced the 

 Alps and the Andes are known to us by experience, 

 no less than the forces which have raised Etna to 

 its present height; for we learn their amount in 

 both cases by their results. Why, then, do we make 

 a merit of using the latter case as a measure for the 

 former? Or how can we know the true scale of 

 such force, except by comprehending in our view 

 all the facts which we can bring together ? 



