JoLY — An Estimate of the Geological Age of the Earth. 35 



The chlorine will be allocated as follows among these elements : — 



4'71 units of weight of iron take up 9"0 units of chlorine nearly; 3'53 units of 

 calcium join with 6'3 units; 2'64 units of magnesium take up 7"6 units; 2'35 

 units of potasium, take up 2'14 units, and 2'68 units of sodium unite with 4*1 units 

 of chlorine. From this it follows, that the chlorine taken up by the sodium bears 

 to the total amount of acid neutralised the ratio of 1 to 7*5, If then there had not 

 been any supply of chlorine subsequently from the rocks, as there has been, 

 this would represent the fraction of the present sodium chloride which was, with 

 comparative rapidity, thrown into the primeval ocean, in the first stages of denu- 

 dation. In other words, of the entire quantity of HCl at that early period neutra- 

 lised by reaction with the constituents of the rocks, only 14 per cent, can have 

 been expended in bringing the sodium into solution as sodium chloride. 



If, therefore, we estimate the chlorine in the original ocean, we may, on the 

 foregoing basis, take 14 per cent, of this as having existed in it as sodium chloride. 



In estimating the chlorine in the primeval ocean, we have to consider that 

 what is now in it is in excess, to some extent, of what originally existed in it by 

 the amount that has been discharged by the rivers during the subsequent history 

 of the Earth. Clarke shows that careful analysis of rocks reveals this element in 

 many rocks wherein it had previously not been looked for. He estimates that 

 it exists to the extent of 0-01 per cent, of the original crust.* In river discharges 

 it will be seen {ante') to amount to no inconsiderable amount, entering chiefly as 

 chloride of sodium, but also as lithium and ammonium chloride. The chloride of 

 sodium is undoubtedly partly derived from the sea itself. It enters into the com- 

 position of rain-water in districts bordering or near the sea. It would appear 

 that further inland it is an inappreciable constituent of rain-water. At Rotham- 

 stead, the average of seventy-one analyses afforded 0'33 of chlorides in 100,000. 

 At Land's End, this rose to 21*8 in 100,000. On the west and east coasts of 

 Scotland, it is 1-19 and 1-26 respectively per 100,000. In London, it is 0-12, and 

 in Ootacamund, India, it is only 0-04 per 100,000 parts, t the latter town being 

 some three hundred miles from the coast in South India. The amount in British 

 rivers free from pollution is 1 in 100,000; and evidently, as these represent a con- 

 centration to one-third of the rainfall, this amount would be accounted for by 

 the chlorine carried from the sea. 



This is not the case with the great rivers of the world. Many of these must 

 derive their chlorides from the rocks by solvent denudation.^ Some deduction 



* Bulletin U.S. Geological Survey, No. 148, j). 13. See also Biseliof's "Chemical and Physical 

 Geology." 



f Thorp's " Dictionary of Applied Chemistry " — Article, " "Water." 



J See Bischofs "Chem. Geology," chap vii., vol. i. English Edition, 1854. Bischof thinks the 

 rivers can carry back to the sea only very little from the beds of rocksalt (p. 111). 



