SEA-SALT AND GEOLOGIC TIME 



By H. S. SHELTON, B.Sc. 



The present short article is a reversion to an aspect of the 

 subject of geologic time which I had thought to be settled, 

 and to require no further research or controversy. In my 

 review of Mr. Holmes's book ! I commented strongly on his 

 ignorance of current literature. I now find that the same 

 imperfect acquaintance with recent discussion and research is 

 shared by the writer who is responsible for putting forward the 

 amount of sodium in the sea as an index of geologic time. I 

 assume, of course, that ignorance is the explanation, for I take it 

 that no man of science of recognised position, when the errors of 

 his research had been pointed out, would deliberately ignore the 

 fact, and proceed as if his work was a valid contribution to the 

 advancement of science. My excuse, therefore, for writing an 

 article containing nothing material which I have not previously 

 published is the following passage, for which Sir Ernest 

 Rutherford and Prof. Joly are jointly responsible : 



11 But it is certain that, if the higher values so found are 

 reliable, the discrepancy with estimates of the age of the ocean, 

 based on the now well-ascertained facts of solent denudation, 

 raises difficulties which at present seem inexplicable." 2 



The values of geologic time referred to, based on radioactive 

 methods, especially the age of pleochroic haloes, I propose to 

 criticise on a future occasion. There are good grounds, which 

 cannot be stated here, for thinking that all attempts to assess 

 exact times for particular geologic epochs by calculation either 

 of the lead ratios of uranium minerals or otherwise are prema- 

 ture, and are based on an imperfect realisation of the complexity 

 of the subject. The object of the present article, however, is to 

 repeat 3 the arguments which show that the alternative method 

 based on the salt-content of the ocean is of no value whatever. 



1 This journal, July 1913. 



2 Philosophical Magazine, May 1913, p. 657. 



3 The previous statements are: Journal of Geology, Feb. -March 1910 ; Con- 

 temporary Review, Feb. 191 1. 



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