XCVi PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 1909, 



This gives an average of 37,920 tons per cubic mile of river- 

 water, and, taken in connexion with Joly's estimate, would lead 

 to a period of 57 millions of years. 



Combining all three results, we obtain : — 



Discharge. Sodium. 



North America 225'622 10,423,403 



South America 748"834 10,076,230 



Europe 68757 2,607,368 



1,043-213 29,107,001 



or an average of 27,900 tons of sodium to the cubic mile, and 

 a period of 90x|i^=78 millions of years, approximately. 



So far we have assumed that the sodium met with in the 

 river-water has been contributed ab ovo, as it were : that is, 

 we assume it to have remained locked up in the terrestrial rocks 

 since the first consolidation of the crust down to a comparatively 

 recent time, when it was liberated by disintegration and trans- 

 ferred to the waters of some running stream. The essence of this 

 disintegration is supposed to lie in the transformation of silicates 

 into carbonates, with the simultaneous extrication of silicic acid. 

 The existence of argillaceous deposits, which form so large a part 

 of the stratified crust, implies some such transformation, and the 

 presence of silicic acid in existing rivers shows that it is still in 

 continual progress at the present day. 



As a natural inference, we should expect to find the sodium in 

 our rivers in the state of carbonate ; while, as a matter of fact, the 

 greater part of it exists as chloride, and the remainder as sulphate. 

 There is no difficulty in accounting for the presence of the sul- 

 phuric-acid radicle, but the chlorine is enigmatical and disquieting. 



Chlorine is well known to occur in falling rain-water. The 

 winds which agitate the sea tear off the breaking crests of the 

 waves and sweep the spray along with them. Along the coast, 

 so often fringed with a margin of boiling surf, this action is 

 especially marked. The fine particles of spray are so minute 

 that they are often carried far inland. It is indeed conceivable 

 that under the influence of evaporation their dimensions might 

 become so far reduced that at length nothing might remain of 

 them but a minute residue of sea-salt, and this might fall as an 

 impalpable snow even over desert-regions. Some observers, par- 

 ticularly those living near the sea-coast, have been so impressed 



