188 THE PAST AND FUTURE OF GEOLOGY. 



the rectilinear fracture of a county with a displacement of thousands of 

 feet. 



In taking into consideration the weight of the evidence where the 

 series is so variable and irregular, it is clear that the increment of value 

 is in i)roportion to the increment of time. One phase of the insect life, 

 one year's record of temperature, a century's observation of the volcano, 

 give evidence which, although of value 2^^'^ tanto, as one link in the 

 chain, is entirely inconclusive when applied to the whole leugth. So in 

 respect to such geological changes as those just named, the value of our 

 experience is only in the proportion of the length thereof to the duration 

 or cyale of the phenomenon under investigation. Thus the elevation of 

 mountain ranges have been events of rare and distant occurrence. Sup- 

 posing, as has been estimated, that all the great chains can be referred 

 to thirteen principal epochs; or, taking subordinate ranges, that the 

 elevation of the mountain-chains of the Old World be limited to twenty 

 such periods. Divide geological time (since the sufficient consolidation 

 of the crust of the earth) by this or even by double this number, and we 

 may form some conception of the length of the cycles involving changes 

 of this magnitude. What that time is it is impossible to say ; we can only 

 feel how infinitely it exceeds all our limited experience. With respect 

 thereto, the experience of five hundred years is no doubt of value — one or 

 two thousand years add further to it; but, after all, how insignificant that 

 duration of time is compared to the time over which the cycle extends. 

 It may be as 1 : 100, or it may be as 1 : 200, or more. And I shall show 

 further on (p. 47) that there are circumstances which indefinitely extend 

 even these proportions. I conclude, therefore, that our experience in 

 these cases is by far too limited to furnish us with reliable data, and that 

 any attempt to reason solely from part to the whole must prove falla- 

 cious. 



Another argument adduced in support of this theory is, in my opinion, 

 equally untenable. It is asserted that, taking the degree of elevatory 

 force now in operation, and allowing quantity of time, the repetition of 

 the small changes on the surface witnessed by us would produce, in 

 time, results of any known magnitude, i. e., that the force which could 

 elevate a district 5 feet in a century would suffice in one hundred thou- 

 sand years to raise it 5,000 feet. This reasoning might be conclusive, if 

 we had cause to suppose that the force were uniform and constant, but 

 even our limited experience shows this to be irregular and paroxysmal; 

 and although the eflects indicate the nature of the force, they in no way 

 give us a measure of its degree. 



Before I i)roceed further I must remove two objections which have 

 been urged against what has been called the cataclysmic theory in oppo- 

 sition to the uniformitarian theory— both terms in themselves inaccurate 

 from their exaggeration, as all such terms usually are. One is, that we 

 require forces other than those which we see in operation ; and the other, 

 that it is unnecessarily sought to do by violent means that which can 



