JoLY — An Estimate of the Geological Age of the Earth. 53 



cent., and the KoO saved to be 85 per cent., which is evidently at variance 

 with the soil analysis. 



The discordance appears to be set at rest in the light of what we have already 

 stated regarding the retention of potasli in soils, recollecting that the surface soil 

 will be poorest in potash, whether by loss to vegetation, or by leaching out of 

 soluble salts retained in the deeper lying parts. The matter is stated as follows 

 by MendeleefS* : — 



" The primary rocks contain an almost equal proportion of potassium and 

 sodium. But in sea-water, the compounds of the latter metal predominate. 

 It may be asked, what became of the compounds of potassium in the dis- 

 integration of the primary rocks, if so small a quantity went to the sea-water ? 



" They remained with the other products of the decomposition of the primary 

 rocks. When Granite or any other similar rock-formation is disintegrated, there 

 are formed, besides the soluble substances, also insoluble substances — sand and 

 finely divided clay, containing water, alumina, and silica. This clay is carried 

 away by the water, and is then deposited in strata. It, and especially its 

 admixture with vegetable remains, retains compounds of potassium in a greater 

 quantity than those of sodium. This has been proved with absolute certainty to 

 be the case, and is due to the absorptive poiver of the soil. If a dilute solution of a 

 potassium compound be filtered through common mould used for growing plants, 

 containing clay and the remains of vegetable decomposition, this mould will be 

 found to have retained a somewhat considerable percentage of the potassium 

 compounds. If a salt of potassium be taken then during the filtration, an 

 equivalent quantity of a salt of calcium — which is also found as a rule in soils — 

 is set free. Such a process of filtration through finely divided earthy substances 

 proceeds in nature, and the compounds of potassium are everywhere retained by 

 the friable earth in considerable quantities. This explains the presence of so 

 small an amount of potassium salts in the waters of rivers, lakesj streams, and 

 oceans, where the lime and soda have accumulated." 



This "absorptive power of the soil," according to Professor IIilgard,t is more 

 displayed in arid than in humid regions. 



The conclusion of the whole matter appears to be that, whereas the sodium 

 compounds tend to accumulate in the waters of the ocean, the potassium compounds 

 tend to be stored in the solid form or retained upon the land ; and that to the 

 causes which bring about this separation, and not to any differences in part 

 processes of denudation, the remarkable scarcity in the ocean of potassium 

 relatively to sodium is to be ascribed. J 



* Loc. cit., Vol. I., p. 546, 547. 



f Quoted by Merrill. Treatise on "Rocks, Rock "Weathering, and Soils," pp. 369-370. 



X The Palagonite coating on basic volcanic glass — apparently derived by a hydration and alteration of 



