114 THE WONDERFUL CENTURY. CHAP. xn. 



than have ever been experienced during the historical 

 period. But modern convulsionists do not confine 

 themselves to this alone, but maintain that, as a rule, 

 all the great natural forces tending to modify the surface 

 of the earth were more powerful and acted on a larger 

 scale than they do now. On the ground of mere proba- 

 bility, however, we have no right to assume a diminution 

 rather than an increase of natural forces in recent times, 

 unless there is some proof that these forces have dimin- 

 ished. Sir Charles Lyell shows that the cases adduced 

 as indicating greater forces in the past are fallacious, and 

 his doctrine is simply one of real as against imaginary 

 forces. 



But our modern objectors have another argument, 

 founded upon the admitted fact that the earth has cooled 

 and is slowly cooling, and was probably once in a molten 

 condition. They urge that in early geological times, 

 when the earth was hotter, the igneous, aqueous, and 

 aerial forces were necessarily greater, and would pro- 

 duce more rapid changes and greater convulsions than 

 now. This is a purely theoretical conclusion, by no 

 means sure, and perhaps the very reverse of what really 

 occurred. There are two reasons for this belief, which 

 may be very briefly stated. After the earth's crust was 

 once formed it cooled very slowly, and the crust became 

 very gradually thicker. So far as the action of the 

 molten interior on the crust may have produced convul- 

 sions they should become not less, but more violent as 

 the crust becomes thicker. With a thin crust any inter- 

 nal tension will be more frequently relieved by fracture 

 or bending, and the resulting disturbances will be less 

 violent; but as the crust becomes thicker, internal ten- 



