52 JoLY — A71 Estimate of the Geological Age of the Earth. 



The anal}'ses show that the mineral may vary in composition. " All that can 

 be said is that the glauconite now forming at the bottom of the sea is, like the 

 glauconite of geological formations, a hydrous silicate of potash and of ferric oxide, 

 containing always variable 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 sea- 

 weeds. A very considerable amount must exist in the immense masses of vegeta- 

 tion in the shallower waters of the sea. 



There is further a very interesting manner in which potash is abstracted from 

 the sea, and returned to the land, which must, in its extension over Geological 

 Time, have served to return immense quantities 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 annually 

 receives from the atmosjohere, by means of rain, 8 "2 kilogrammes of KCl, and 

 S'O kilogrammes of K0SO4, amounting to a total of 7 '9 kilogrammes of jiotassium. 

 This is 1*23 tons of potassium per square mile per annum, or 1'48 tons of K2O. 



Now it is a well-known fact that, whereas sodium salts so bi-ought to the land, 

 are again freely yielded up by the soils, potash salts are retained. Vegetation 

 also requires these salts as an essential constituent, sodium salts are not essential to 

 vegetation, f 



In connexion with this, the relative losses of the alkalies as shown in the 

 table {ante), compiled from Mr. Merrill's work on "Rock Weathering" should 

 be considered. It appears from that table that the average loss of potash, in the 

 soils taken as examples, was 56'3 per cent., 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 variance with 

 the broad facts of rock-chemistry to which we have been frequently referring. 

 Thus, if we effect for potash a similar calculation to that carried out for soda, and 

 estimate from the average potash percentages in the sedimentary detrital rocks, 

 and of the primary crust-rock, the amount of potash lost and saved (assuming as 

 before the alumina as the constant factor), we find the K2O lost to be 15 per 



* Loc. cit., p. 134. 



f See Eoscoe's and Schorlemmer's Cliemistry, 11., Part i., p. 57; also Mendeleeif's Chemistry, 1897, 

 I., p. 546. 



