LIFE ON THE EARTH. 123 



accumulation in the sea ; that some of these changes 

 of conditions can be traced to vast and ancient move- 

 ments in the crust of the earth, perhaps the accu- 

 mulated consequence of slow variation in the con- 

 dition of the interior, but certainly productive of 

 great derangement of rate in the accumulation of 

 earthy sediments at the surface. In the full an- 

 nouncement of this view of the earth being subject 

 to great disturbance from within, disturbance grow- 

 ing less and less with time no one has been more 

 explicit than Leibnitz, who conceived the idea of a 

 globe once fluid with heat, then slowly cooling, chang- 

 ing its dimensions, and breaking up its surface in 

 confusion; ' donee, quiescentibus causis atque equi- 

 libratis, consistentior emergeret rerum status.' The 

 two theoretical views thus strongly contrasted may 

 be represented by a few letters any known natural 

 effect or amount of work performed (E), is a product 

 of the power operating (P), and the time con- 

 sumed (T), or E = PT. If P can be determined, T 

 becomes known. If P is assumed with uncertainty, 

 as by the Uniformitarians, T is equally uncertain. 

 The really useful problem then is to find the 

 limits of the power, which can only be done by a 

 knowledge of the law according to which the con- 

 ditions influencing its value depend. Such a law 

 is supposed to be discoverable in the decreasing 



