PALAGONITE EOCK. 155 



concerned in the chemical phenomena of Ice- 

 land is a rock called Palagonite. The consti- 

 tuents of this rock are, silica, iron, alumina, 

 lime, magnesia, potash, soda, and water. These 

 ingredients, -united in one substance, and ex- 

 posed to the volcanic gases which are continu- 

 ally penetrating the earth, become acted upon 

 in a variety of ways, and form with the latter 

 and each other a number of different combina- 

 tions. The gases thus permeating the strata 

 beneath the surface, consist, as is generally the 

 case, of, sulphurous acid, sulphuretted hydro- 

 gen, carbonic acid, and hydrochloric acid. The 

 palagonite becomes, by the chemical decompo- 

 sitions thus set up, converted into beds of fer- 

 ruginous clay, interpenetrated by beds of gyp- 

 sum or sulphate of lime. Around the smoking 

 orifices of the fumeroles, thick crystalline 

 crusts of sulphur are deposited. The source of 

 this sulphur appears to be the mutual decom- 

 position of the volcanic gases, sulphurous acid, 

 and sulphuretted hydrogen, the result of which 

 decomposition is the deposition of sulphur. 

 The existence of the latter gas in the column 

 of gaseous emanations rising from one of the 

 highest craters of Mount Hecla, was not sen- 

 sible to test paper, but was detected . in a very 

 peculiar manner. This gas, when burnt in con- 

 tact with air, undergoes a peculiar process of 



