THE AGE OP THE EAETH. 15 



by Mr. Alfred Wallace. Here it is* : — " So far as I can at 

 present ?ee, the lapse of time since the beginning of the 

 Cambrian system is probably less than 17,000,000 years, 

 even when computed on an assumption of uniformity, 

 which to me seems contradicted by the most salient facts 

 of geology. Whatever additional time the calculations 

 made on physical data can afford us, may go to the account 

 of pre-Cambrian deposits, of which at present we know too 

 little to serve for an independent estimate." 



§ 8. In one of the evening Conversaziones of the British 

 Association during its meeting at Dundee in 1867 I had a 

 conversation on geological time with the late Sir Andrew 

 Ramsay, almost every word of which remains stamped on 

 my mind to this day. We had been hearing a brilliant and 

 suggestive lecture by Professor (now Sir Archibald^ Geikie 

 on the geological history of the acticms by which the existing 

 scenery of Scotland Avas produced. I asked Ramsay how long 

 a time he allowed for that history. He answered that he 

 could suggest no limit to it. I said, " You don't suppose 

 things have been going on always as they are now? You 

 don't suppose geological history has run through 1,000,000,000 

 years? " "Certainly I do." "10,000,000,000 years ? " " Yes.^' 

 " The sun is a finite bod}^ You can tell how many tons it is. 

 Do you think it has been shining on for a million million 

 years ? " " 1 am as incapable of estimating and under- 

 standing the reasons which you physicists have for limiting 

 geological time as you are incapable of understanding the 

 geological reasons for our unlimited estimates." I answered. 

 ^' You can understand physicists' reasoning perfectly if you 

 give your mind to it." I ventured also to say that physicists 

 were not wholly incapable of appreciating geological diffi- 

 culties ; and so the matter ended, and we had a friendly 

 agreement to temporarily differ. 



§ D. In fact, from about the beginning of the century till 

 that time (1867), geologists had been nurtured hi a 

 philosophy originating with the Huttonian system : much 

 of it substantially very good philosophy, but some of it, 

 essentially unsound and misleading : witness this, from 

 Playfair, the eloquent and able expounder of Hutton : — 



" How often these vicissitudes of decay and renovation have been 

 repeated is not for us to determine ; they constitute a series of which as 

 the author of this theory has remarked, we neither see the beoinning nor 



* " Tlie Age of the Earth," Nature, April 4t]i, 1895. 



