Joty—An Estimate of the Geological Age of the Earth. 30 
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 joi with 6°3 units; 2°64 units of magnesium take up 7:6 units; 2°36 
units of potasium, take up 2°14 units, and 2°68 units of sodium unite with 4:1 units 
of chlorme. 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,f 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.t Some deduction 
* Bulletin U.S. Geological Survey, No. 148, p. 13. See also Bischof’s ‘‘ Chemical and Physical 
Geology.” 
} Thorp’s * Dictionary of Applied Chemistry ”—Article, ‘‘ Water.” 
{ See Bischof’s ‘‘Chem. Geology,” chap vii., vol. 1. English Edition, 1854. Bischof thinks the 
rivers can carry back to the sea only very little from the beds of rocksalt (p. 111). 
