METAMORPHOSED FUCOID SCHISTS IN SCANDINAVIA. 161 



new decomposition, change into sulphate of alumina. If, on the contrary, car- 

 bonate of lime acts upon the sulphate of iron, gypsum will of course be 

 produced. 



The potash which has been formed by the decomposition of the sulphuret 

 of potassium acts upon the clay (silicate of alumina) and forms with it an in- 

 soluble combination, which probably also contains water. To ascertain this 

 fact, which appears to me of high importance in the explanation of geological 

 phasnomena, I have several times exposed ferruginous clay to the action of 

 a solution of sulphuret of potash with the following result : — 



39"043 grains, English weight, of ferruginous clay from the tertiary for- 

 mation of Stowerhoved in the island of Fyen, were analysed by means of 

 fluoric acid, and gave 0'184 grain chloride of potassium = 0*47 per cent, 

 chloi'ide of potassium = 0*30 per cent, of potash. 



41 '957 grains of the same clay, which for some days had been exposed to 

 the action of a solution of sulphuret of potassium, gave, by being treated with 

 fluoric acid, &c., 0*930 grain = 2*22 per cent, of chloride of potassium = 1*42 

 per cent, of potash. 



61*653 grains of the same clay, which likewise had been exposed to the 

 action of a solution of sulphuret of potassium, gave 1*719 grain = 2*79 per 

 cent, of chloride of potassium = 1*76 per cent, of potash. 



The objection might be made that this potash was part of the solution 

 which had not been properly washed out of the clay. This however is not the 

 case, because when the clay had been washed on the filter until hardly any 

 trace of soluble substance was left after the washing, water was evaporated, 

 was taken from the filter, mixed up with a great quantity of water, and again 

 collected on a new filter. It could not be avoided that the sulphuret of iron 

 was oxidized during this long process of washing, and that the black colour 

 of the clay slowly changed into yellowish-red. But afterwards, when the clay 

 was tested, it contained a very small quantity only of sulphuric acid, and an 

 action seems to have taken place between the sulphate of iron and the potash 

 combined with the clay, by which sulphate of potash was formed, which being 

 soluble in water of course must diminish the quantity of potash combined 

 with clay. In one instance I succeeded in washing the clay so quickly, that no 

 observable oxidation took place, but unfortunately it had not been weighed 

 beforehand, and thus although the quantity of potash seemed to be consider- 

 ably greater than in the other experiments, it cannot be used as an argument. 

 Is is highly probable that by a longer action between the ferruginous clay 

 and the sulphuret of potash, a larger quantity of potash will be combined with 

 the clay ; but at all events these experiments show, that whenever sea-weeds 

 in the last state of decomposition act upon ferruginous clay, iron pyrites is 

 formed and a quantity of potash is combined with the clay into a compound 

 which is insoluble in water. 



Since all the analysed species of the Fucus tribe, belonging to the most 

 different countries, from Greenland to the Equator and the Cape of Good 

 Hope, and to the different families, contained considerable quantities of sul- 

 phuric acid and potash, they all must have the eff"ect described, whenever 

 the other circumstances occur ; and we may fairly infer, that even the fucoidal 

 plants of the earlier periods of the world would produce similar changes in 

 the clay of the sea. 



The Silurian strata of the Scandinavian peninsula and the island of Bornholm 

 contain in their oldest parts large beds of aluminous slate, which is used in a 

 great number of manufactories for making alum, and this alumnious slate 

 has the great advantage over those slates of the carboniferous system of 

 Germany and a part of France, that it contains the sufficient quantity of potash 

 1844. M 



