340 AGE OF THE EARTH AS AN ABODE FITTED FOR LIFE. 



or the erosion of space between the ranges of cbalk hills, known as the 

 North and Sonth Downs, at f/tree hundred millions of years. The grounds 

 for forming this estimate are of course of the vaguest description. It 

 may be possible, perhai)s, that the estimate is a hundred times too 

 great, and that the real time elapsed did not exceed three million years, 

 but, on the other hand, it is just as likely that the time which actually 

 elapsed since the first commencement of the erosion till it was nearly 

 as complete as it now is, was really a hundred times greater than his 

 estimate, or thirty thousand millions of years." 



7. Thus Jukes allowed estimates of anything from 3,000,000 to 

 30,000 millions as the time which actually passed during the denudation 

 of the Weald. On the other hand. Professor Phillips in his Eede lecture 

 to the University of Cambridge (1860), decidedly prefers 1 inch per 

 annum to Darwin's 1 inch per century as the rate of erosion, and says 

 that most observers would consider even the 1 inch per annum too 

 small for all but the most invincible coasts. He thus, on purely geolog- 

 ical grounds, reduces Darwin's estimate of the time to less than one 

 one hundredth. And, reckoning the actual thicknesses of all the known 

 geological strata of the earth, he finds 96,000,000 years as a possible 

 estimate for the antiquity of the base of the stratified rocks, but he 

 gives reasons for supposing that this may be an overestimate, and he 

 finds that from stratigraphical evidencealone we may regard the antiq- 

 uity of life on the earth as possibly between 38,000,000 and 96,000,000 

 of yeais. Quite lately a very careful estimate of the antiquity of strata 

 containing remains of life on the earth has been given by Professor 

 Sollas, of Oxford, calculated according to stratigraphical principles 

 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 uniformity, which to me seems 

 contradi(;ted by the most salient facts ot geology. Whatever addi- 

 tional time the calculations made on physical data can afford us may 

 go to the account of pre-Cambrian deposits of which at x)resent 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 geolog- 

 ical time with the late Sir Andrew Eamsay, 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 actions by which the existing 

 scenery of Scotland was produced. I asked Eamsay 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 body. You can tell how many tons 

 it is. Do you think it has been shining on for a million million years'?" 



1 ''The Age of the Earth," Nature, April i, 1895. 



