Sir A. Oeilde — Age of the Earth. 461 



of his papers is there an admission that geology and palceontology, 

 though they have again and again raised their voices in protest, have 

 anything to say in the matter tliat is worthy of consideration. 



It is difficult satisfactorily to carry on a discussion in which your 

 opponent entirely ignores your arguments, while you have given the 

 fullest attention to his. In the present instance geologists have 

 most carefully listened to all that has been brought forward from 

 the physical side. Impressed by the force of the physical reasoning, 

 they no longer believe that they can make any demands they may 

 please on past time. They have been willing to accept Lord Kelvin's 

 original estimate of 100 millions of years as the period within which 

 the history of life upon the planet must be comprised; while some 

 of them have even sought in various ways to reduce that sum nearer 

 to his lower limit. Yet there is undoubtedly a prevalent misgiving, 

 whether in thus seeking to reconcile their requirements with the 

 demands of the physicist they are not tying themselves down 

 within limits of time which on any theory of evolution would have 

 been insufficient for the development of the animal and vegetable 

 kingdoms. 



It is unnecessary to recapitulate before this Section of the British 

 Association, even in briefest outline, the reasoning of geologists 

 and palseontologists which leads them to conclude that the history 

 recorded in the crust of the earth must have required for its trans- 

 action a much vaster period of time than that to which the physicists 

 would now restrict it.^ Let me merely remark that the reasoning 

 is essentially based on observations of the present rate of geological 

 and biological changes upon the earth's surface. It is not, of course, 

 maintained that this rate has never varied in the past. But it is 

 the only rate with which we are familiar, which we can watch and 

 in some degree measure, and which, therefore, we can take as 

 a guide towards the comprehension and interpretation of the past 

 history of our planet. 



It may be, and has often been, said that the present scale of 

 geological and biological processes cannot be accepted as a reliable 

 measure for the past. Starting from the postulate, which no one 

 will dispute, that the total sum of terrestrial energy was once greater 

 than it is now and has been steadily declining, the physicists have 

 boldly asserted that all kinds of geological action must have been 

 more vigorous and rapid during bj'gone ages than they are to-day ; 

 that volcanoes were more gigantic, earthquakes more frequent and 

 destructive, mountain upthrows more stupendous, tides and waves 

 more powerful, and commotions of the atmosphere more violent, with 

 more ruinous tempests and heavier rainfall. Assertions of this kind 

 are temptingly plausible and are easily made. But it is not enough 

 that they should be made; they ought to be supported by some kind 

 of evidence to show that they are founded on actual fact and not on 



^ The geological arguments are briefly given in my Presidential Address to the 

 British Association at the Edinburgh Meeting of 189"2. The biological arguments 

 were well stated, and in some detail, by Professor Poulton in his Address to the 

 Zoological Section of the Association at the Liverpool Meeting of 1896. 



