Joty—An Estimate of the Geological Age of the Earth. 53 
cent., and the K,O 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 potash 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 Mendeleeft* :— 
“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 msoluble 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 power of the soil. i 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 caleium—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, lakes, streams, and 
oceans, where the lime and soda have accumulated.” 
This “‘absorptive power of the soil,” according to Professor Hilgard,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.t 
* Loe. cit., Vol. 1., p. 546, 547. 
} Quoted by Merrill. Treatise on ‘‘ Rocks, Rock Weathering, and Soils,” pp. 869-370. 
3 pp 
{ The Palagonite coating on basic volcanic glass—apparently derived by a hydration and alteration of 
