152 On the Origin and Composition of Basalt. 



The mass which does not gelatinize yields, when what ap- 

 pears to be magnetic iron is abstracted from the oxidulated 

 oxide of iron, 



100.00 



This result does not agree precisely with that of any other 

 mineral, with respect to the component parts, but it approaches, 

 in some measure, to anorthite, a species of felspar discovered by 

 G. Rose. Anorthite is entirely decomposed by concentrated mu- 

 riatic acid. It likewise contains a considerable quantity of mag- 

 nesia, but what particularly deserves notice is, that no other fos- 

 sil containing much magnesia gelatinizes with acid. The quan- 

 tity of silica and lime in that part of basalt which gelatinizes 

 with acids, agrees completely with that contained in anor- 

 thite. But, on the other hand, anorthite contains a far greater 

 quantity of aluminous earth, considerably less magnesia, and no 

 alkali. On the whole, it appears that that part of basalt which 

 gelatinizes with acids, is the regular mass from which the vari- 

 ous crystals are developed, that occur so frequently in basalt. 

 For example, it is easy to perceive, that in consequence of the 

 disappearance of magnesia, Labrador felspar, that universal com- 

 ponent part of dolerite and syenite, as well as of many meteoric 

 stones, stilbit so frequent in basalt, as well as chabasie, prehnite 

 and arragonite, will be found in the mass. 



The portion which does not gelatinize has nearly the same 

 component parts as augite. 



The analysis of basalt'from HohenstofFeln in Hegau is not yet 

 quite completed. The proportion of the gelatinizing part to that 

 which does not gelatinize is = 6.197:3.303, and it deserves to 

 be noticed, that it approaches very nearly to the basalt from 

 Sletten. . . . , 



