Cii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May I909, 



24,100, the number of tons to the cubic mile used by Joly in his 

 calculation, we obtain 106 millions of years for the age of the 

 Ocean. 



May this be regarded as a maximum, a definitely ascertained 

 limit, which may not have been reached, but cannot possibly have 

 been exceeded? Scarcely. Doubts may well be entertained on 

 this point, for although no sodium known to have been derived 

 from the sea enters into the calculation, yet some is still supplied 

 from ancient stores, and these may possibly be in process of 

 depletion at an exceptionally rapid rate. This is, in fact, suggested 

 by the excessive amount of sodium contained in the rivers which 

 drain the Pacific slope of the continent. The neglected sodium 

 supplied by hot springs may or may not compensate for this. 



On the other hand, if we now turn to South America, we perceive 

 at once that to eliminate all the sodium existing in combination 

 with chlorine is too drastic a proceeding, for it leaves the Amazon 

 absolutely destitute of this constituent. This surprising result 

 increases our mistrust of the analyses, or at least of the methods 

 by which samples of the water were obtained for investigation. 

 We will not on this account, however, at once abandon our present 

 train of thought, and we will introduce the rivers of South America 

 into our calculation ; I give below the quantities of sodium, in 

 excess of the chlorine-ratio, found in the three South American 

 rivers already mentioned. 



Table VI. 

 Biver. Sodium. Silica. 



Amazon 23,982,000 



Uruguay 176,900 3,848,000 



LaPlat'a 7,287,000 14,970,000 



7 ,463,900 42,800,000 



If we combine the results obtained from the two continents, we 

 may to some extent effect that compensation which would be 

 complete if we were able to take into account the whole river- 

 drainage of the world. 



Volumes. Sodium. Silica. 



North America 227708 4,640,475 12,668,970 



South America 748-834 7,463,900 42,800,000 



976-54 2 12,104,375 55,468,9 70 



The quantity of sodium in one cubic mile, found by dividing the 



