28 EVOLUTION 



found to show a very fair measure of agreement,; and 

 they led to the conclusion that considerably less than 

 a hundred million years has elapsed since the first for- 

 mation of seas upon this planet, an event which must 

 have preceded the possibility of aqueous geological 

 action and the existence of living organisms 



Allowing for the circumstance that geological pro- 

 cesses may have gone forward with considerably 

 greater rapidity during the earlier periods of the 

 earth's history than is the case at the present day, the 

 time thus allowed by the physicist is generally regarded 

 by geologists as too little. Reckoning from the known 

 rate of denudation, which is* of course t the same as 

 the rate at which the same material is deposited 

 beneath the sea, Geikie, who admitted, however, that 

 such data are only of a very rough description, 

 concluded that the space of a hundred million years 

 would afford sufficient time for the laying down 

 of the known aqueous strata. But there can be 

 little doubt that the lower metamorphosed rocks 

 represent a much longer period of time than 

 the primary, secondary, and tertiary epochs added 

 together ; consequently, the respective estimates of 

 Lord Kelvin and the geologists appear to be contra- 

 dictory. The recent discovery of the enormous quan- 

 tities of energy stored up in radio-active substances 

 introduces a serious modification into the mathematical 

 argument from astronomical data, and Sir George 

 Darwin ' sees no reason for doubting the possibility 

 of augmenting the estimates of solar heatj as derived 

 from the theory of gravitation, by some such factor 



