668 



SCIENCE. 



[N. S. Vol. IX. No. 928. 



finds that from stratigraphical evidence 

 alone we may regard the antiquity of life 

 on the earth as possibly between 38 millions 

 and 96 millions of j^ears. Quite lately a very 

 careful estimate of the antiquity of strata 

 containing remains of life on the earth has 

 been given by Professor SoUas, of Oxford, 

 calculated according to stratigraphical prin- 

 ciples which had been pointed out by Mr. 

 Alfred Wallace. Here it is*: " So far as 

 I can at present see, 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 uni- 

 formity, which to me seems contradicted 

 by the most salient facts of geology. What- 

 ever 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 sug- 

 gestive lecture by Professor (now Sir Archi- 

 bald) Geikie on the geological history of 

 the actions by which the existing scenery 

 of Scotland was produced. I asked Eamsay 

 how long a time he allowed for that historj'. 

 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 his- 

 tory has run through 1,000,000,000 years '?" 

 " Certainly I do." " 10,000,000,000 years?" 

 " Yes." " The sun is a finite body. You 

 can tell how many tons it is. Do you think 

 it has been shining on for a million million 

 years?" " I am as incapable of estimating 

 and understanding the reasons which you 

 physicists have for limiting geological time 



*'The Age of the Earth, ' Nature, April 4, 1895. 



as you are incapable of understanding the 

 geological reasons for our unlimited esti- 

 mates." 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 difficulties ; and 

 so the matter ended, and we had a friendly 

 agreement to temporarily differ. 



§ 9. In fact, from about the beginning of 

 the century till that time (1867), geologists 

 had been nurtured in a philosophy origi- 

 nating with the Huttonian system : much 

 of it substantially very good philosophy, 

 but some of it essentially unsound and mis- 

 leading ; witness this, from Playfair, the elo- 

 quent and able expounder of Hutton : 



' ' How often these vicissitudes of decay and renova- 

 tion liave been repeated is not for us to determine ; 

 they constitute a series of which as the author of this 

 theory has remarlced, we neither see the beginning 

 nor the end ; a circumstance that accords well with 

 ^vhat is known concerning other parts of the economy 

 of the world. In the continuation of the different 

 species of animals and vegetables that inhabit the 

 earth, we discern neither a beginning nor an end ; in 

 the planetary motions where geometry has carried 

 the eye so far both into the future and the past we 

 discover no mark either of the commencement or the 

 termination of the present order.'' 



§ 10. Led by Hutton and Playfair, Lyell 

 taught the doctrine of eternity and uni- 

 formity in geology ; and to explain plutonic 

 action and underground heat, invented a 

 thermo-electric ' perpetual' motion on 

 which, in the year 1862, in my paper on 

 the 'Secular Cooling of the Earth,'* pub- 

 lished in the ' Transactions of the Royal 

 Society of Edinburgh,' I commented as fol- 

 lows : 



"To suppose, as Lyell, adopting the chemical hy- 

 pothesis, has done,t that the substances, combining 

 together, may be again separated eleotrolytioally by 

 thermo-electric currents, due to the heat generated by 

 their combination, and thus the chemical action and 



* Reprinted in Thomson and Tait ' Treatise on 

 Natural Philosophy,' 1st and 2d Editions, Ap- 

 pendix D (g). 



t ' Principles of Geology,' Chap. XXXI., ed. 1853. 



