276 AN ESTIMATE OF THE GEOLOGICAL AGE OF THE EARTH. 



hydrous silicate of potash and of ferric oxide, cojitainino^ alAvays varia- 

 ble quantities of alumina, ferrous oxide, magnesia, and often lime." 

 (P. 386.) 



Merrill gives analyses showing that the glauconitic marls of New 

 Jersey contain up to 7 per cent of potash, and remarks on the extent 

 of such beds in the Cretaceous formation of New Jersey.' 



Potash is also taken up by organisms in the sea, more especially by 

 the seaweeds. A very considerable amount must exist in the innnense 

 masses of vegetation in the shallower waters of the sea. 



There is further a verv interesting manner in which potash is 

 abstracted from the sea and returned to the land, which nnist, in its 

 extension over geological time, have served to return iuuncnse quan- 

 tities to the soils of coastal regions. This is by means of rain water. 



In Dr. Angus Smith's work on Air and Rain it is recorded that near 

 Caen, in France, it has been estimated (by M. J. Pierre) that a hectare 

 of land annuall}" receives from the atmosphere, by mean« of rain, 8.2 

 kilograms of KCl and 8 kilograms of KjSO^, amounting to a total of 

 7.9 kilograms of potassium. This is 1.28 tons of potassium per si^uare 

 mile per annum, or 1.48 tons of KjO. 



Now, it is a well-known fact that, whereas sodium salts so brought 

 to the land are again freely yielded up by the soils, potash salts are 

 retained. Vegetation also requires these salts as an essential constitu- 

 ent. Sodium salts are not essential to vegetation.^ 



In connection with this the relative losses of the alkalis, as shown 

 in the table (ante) compiled from Mr. Merrill's work on Rock Weath- 

 ering, should be considered. It appears from that table that the aver- 

 age loss of potash in the soils taken as examples was 56.3 percent, 

 the soda loss being 69.7. According to this the rivers are not carrying 

 sufficient potash into the sea relatively to soda to account for what is 

 going on under the decomposing effects of subaerial agencies. 



We can see, too, that the revelations of the soil analyses are at vari- 

 ance with the broad facts of rock chemistry, to which we have been fre- 

 quently referring. Thus, if we effect for potash a similar calculation 

 to that carried out for soda and estimate from the average potash per- 

 centages in the sedimentar}' detrital rocks and of the primar}^ crust 

 rock the amount of potash lost and saved (assuming, as before, the 

 alumina as the constant factor) we find the KgO lost to be 15 per cent 

 and the KjO 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 the poorest in potash, whether by loss to 



1 Report, p. 134. 



2 See Roscoe's and Schorlemmer's Chemistry, II., Part I., p. 57; also Meudeleeff's 

 Chemistry, 1897, I., p. 546. 



