258 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1&21. 



incredulity, since a score million years was of little more use to 

 geology than the seven days of the Pentateuch. Now that physical 

 evidence allows the age of the earth to be counted by the thousand 

 million years the problem is of less concern to the geologist, except 

 from the hope that the uranium-lead ratio may fix geological dates 

 in years, and from the interest of reconciling the conflicting results 

 of the different methods. 



The geological estimates to which most weight has been attached 

 are based on the saltness of the sea. The salinity argument has been 

 widely accepted as sound in principle; the estimates varied from 

 70,000,000 to 150,000,000 years, and some intermediate length was re- 

 garded as inevitable. Allowances were made for various factors ; but 

 they added only a few per cent to the total, and did not multiply it by 

 ten or more. 



The validity of the salinity argument may be tested by two 

 checks — the supply of chlorine, and the denudation required to 

 account for the amount of sodium ; and as shown by Dr. A. Holmes, 

 each of these indicates a much longer period than the sodium. 



The supply of chlorine in igneous rocks is quite inadequate to 

 convert their sodium into chloride. Most of the sodium chloride 

 in river water is probably marine in origin, and only the sodium in 

 the bicarbonate and sulphate is a fresh addition to the sea. On this 

 ground the salinity estimate should be approximately doubled. 

 Again, to obtain all the sodium in the sea from igneous rocks 

 would involve the denudation of improbable volumes of them, and, 

 at the rate usually accepted, the age of the earth should be multiplied 

 three or four fold. 



The fundamental objections to the salinity argument are against 

 (1) its assumption that the sea was originally fresh, which paleon- 

 tological evidence renders improbable; the oldest fauna, the Cam- 

 brian, has the characteristic of a marine fauna, and the contrast be- 

 tween the fresh water and the marine faunas was as sharp in Paleozoic 

 times as it is to-day; (2) its omission to allow for the large supplies 

 of sodium chloride raised from beneath the earth's surface by mag- 

 matic waters; (3) its assumption of uniform denudation. The earth 

 has probably undergone deformations that led to alternate periods 

 of quick and slow crustal movement; during the times of repose 

 the surface would have been planed down and rivers would have 

 become sluggish and denudation slow. As the earth is now under 

 the influence of a time of quick movement, denudation is faster than 

 the average. A multiplication of the earth's age fivefold for this 

 difference would not be excessive. 



During quick crustal movement volcanic action would be more 

 powerful, the discharge of hydrochloric acid and sodium in hot 



