FORMATION OF CLAYS. 



89 



of water, saturated with carbonic acid, although it is scarcely- 

 affected by being left in contact with cold muriatic acid for 

 twenty-four hours. The analyses given above show that the 

 most widely diffused rocks contain a mixture of silicates, which, 

 being soluble in cold muriatic acid, must be much more easily- 

 attacked than felspar by water holding in solution carbonic acid. 



All minerals and rocks containing silicates of alkaline bases 

 are incapable of resisting the continued solvent action of carbonic 

 acid dissolved in water. The alkalies, with lime and magnesia, 

 will either dissolve alone, or the former will enter into solution 

 along with silica, while the alumina remains behind, mixed or 

 combined with silica. Disintegrated phonolite from Abterode, 

 formed by the action of air and moisture on the solid mineral 

 (the analysis of which is given above), behaves to acids in a 

 manner quite different from the latter. 



The mineral clinkstone contains more than 20 per cent, of 

 ingredients soluble in muriatic acid, whilst the same mineral, 

 when disintegrated, does not contain more than 5 per cent, of 

 soluble constituents.* 



The insoluble portion of disintegrated phonolite is scarcely 

 altered. in composition: in the soluble portion, iron and mangan- 

 ese form the principal constituents : these two oxides exist in the 

 soluble portions of the undisintegrated mineral in the proportion 

 of 11-346 : 2-194 ; and in the disintegrated mineral, 100 parts 

 contain 63-39 of peroxide of iron to 11*3 of peroxide of man- 

 ganese, or nearly the same proportion as the former. 



In the process of disintegration, therefore, the alkalies, lime, 

 and magnesia, have been dissolved and carried away by water 

 along with silica and alumina ; and the residue contains only yV 

 the amount of the alkalies originally present. But as long as 

 the mineral contains a trace of an alkali, or of any base soluble 



* The soluble part of disintegrated 

 clinkstone contains — 



Silica - 13396 



Alumina - - - 5*660 



Potash (Soda) - - 1-074 



Lime .... 



Peroxide of Iron - - 63 396 



Peroxide of Manganese - 11 • 1 32 



Titanic Acid - - 3'396 



