GEOLOGICAL PRINCIPLES. 115 



sions will accumulate, and when relieved by fracture the 

 disturbance will be more violent. 



As regards storms and other aerial disturbances, these 

 also would probably be less violent when the tempera- 

 ture of the whole surface was more uniform as well as 

 warmer, and the atmosphere consequently so full of 

 vapor as to prevent the sun's rays from producing the 

 great inequalities of temperature that now prevail. It 

 is these inequalities that produce the great aerial dis- 

 turbances of our era, which arise from the heated sur- 

 faces of the bare plains and deserts of the subtropical 

 and warm temperate belts. In the equatorial belt 

 (10 each side of the equator), where the heat is more 

 uniform and the surface generally well clothed 

 with vegetation, tornadoes and hurricanes are almost 

 unknown. 



There remains only the action of the tides upon coasts 

 and estuaries, which may have been greater in early geo- 

 logical times, if, as is supposed, the moon was then con- 

 siderably nearer to the earth than it is now. But this is 

 a comparatively unimportant matter as regards geologi- 

 cal convulsions, because its maximum effects recur at 

 short intervals and with great regularity, so that both 

 vegetation and the higher forms of animal life would 

 necessarily be limited to the areas which were beyond its 

 influence. 



It thus appears that, so far from there being any 

 theoretical necessity for greater violence of natural 

 forces in early geological times, there are some weighty 

 reasons why the opposite should have been the case; 

 while all the evidence furnished by the rocks themselves, 

 and bv the contours of the earth's surface, are in favor 



