UNIFORMITY OF CONDITIONS 19 



as Professor George Darwin has pointed out, evidence 

 of uniformity in the strains due to the condition of the 

 atmosphere. 



We can trace the prints of raindrops at various geo- 

 logical horizons, and in some cases found in this country 

 it is even said that the eastern side of the depressions is 

 the more deeply pitted, proving that the rain drove from 

 the west, as the great majority of our storms do to-day. 



When, therefore, we are accused of uniformitarianism, 

 as if it were an entirely unproved assumption, we can at 

 any rate point to a large body of positive evidence which 

 supports our contention, and the absence of any evidence 

 against it. Furthermore, the data on which we rely are 

 likely to increase largely, as the result of future work. 



After this interpolation, chiefly of biological argument 

 in support of the geologist, I cannot do better than bring 

 the geological evidence to a close in the words which 

 conclude Sir Archibald Geikie's address : ' After careful 

 reflection on the subject, I aflirm that the geological 

 record furnishes a mass of evidence which no arguments 

 drawn from other departments of Nature can explain 

 away, and which, it seems to me, cannot be satisfactorily 

 interpreted save with an allowance of time much beyond 

 the narrow limits which recent physical speculation would 

 concede.' 



In his letter to Professor Perry, ^ Lord Kelvin says: — 



* So far as underground heat alone is concerned, you 

 are quite right that my estimate was 100 million, and 

 please remark ^ that that is all Geikie wants ; but I should 

 be exceedingly frightened to meet him now with only 

 20 million in my mouth.' 



We have seen, however, that Geikie considered the 

 rate of sedimentation to be, on the whole, uniform with 

 that which now obtains, and this would demand a period 

 of nearly 400 million years. He points out furthermore 

 that the time must be greatly increased on account of the 

 breaks and interruptions which occur in the series, so 

 that we shall probably get as near an estimate as is 

 possible from the data which are available by taking 450 



* Nature^ Jan. 3, 1895. ^ P. L. and A., vol. ii. p. 87* 



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