86 FORMATION OF SOILS. 



in felspar or felspathic rocks. Felspar* may be viewed as a 

 combination of silicate of alumina with silicate of potash; the 

 last of which being gradually removed by water, leaves behind 

 the porcelain clay. 



It has been shown by Forchammer, that felspar may be de- 

 composed by water of 150° C. (302° F.), and at a pressure cor- 

 responding to this temperature. The water becomes strongly 

 alkaline, and is found to contain silica in solution. The hot 

 springs in Iceland possess a high temperature, and come from a 

 great depth, where they must have been subjected to high pres- 

 sure. Forchammer has shown by analysis that the water of 

 these springs contains the constituents of soda felspars, and of 

 magnesian silicates, minerals of very frequent occurrence in 

 trap districts. There cannot be a doubt that a conversion of 

 crystalline felspar into clay must be proceeding to a great extent 

 at the bottom of these springs. f 



Ordinary water containing carbonic acid acts in precisely 

 the same manner as water at a high temperature, and at a high 

 pressure. 



Polstorf and Wiegmann boiled some white sand with a mixture 

 of nitric and muriatic acids, and after completely removing the 



* COMPOSITION OF FELSPATHIC MINERALS. 



Felspar. Albit. Labrador. A north. 



Silica - - - 56'9 - - 69"8 - - 558 - - 44-5 

 Alumina - - - 17-8 - - 18*8 - - 26"5 - - 34'5 

 Potash - - - 16'3 - - — - — - - — 



Soda - - - — - - 11*4 - - 4-0 - - — 

 Magnesia- - - — - - — - - — - - S'2 

 Lime - - - — - - — - - 11-0 - - 157 

 Protoxide of iron - — - - — - -1*3- -07 



The chemical formula of felspar is Al 2 , 3 3 Si O, + KO, Si 0|, 

 f his formula, when multiplied by three, may be divided into porcelain 

 clay, 3 Ala, O3, 4 Si 3 , and into soluble silicate of potash, 3 Ko, 8 

 SiOt. 



f The dry residue of 28 ounces of the water consisted of— • 

 Gypsum - 

 Sulphate of Soda > 

 Magnesia ) 

 Common Salt 

 Soda - 

 Silica - . . - 



