Sorzas—On the Variolite and Associated Igneous Rocks. 107 
existing mineral composition. It is clear, however, that the original 
material was of a very basic character. Disregarding the water, the 
existing rock contains material which would furnish the following : 
Molecules. 
Ilmenite, — ‘ : : ‘ 3 1 
Magnetite (and Chromite), : ‘ 2 
Olivine (Mg;Fe,Si,), . § s : 4 (of M,8i0,) 
Anorthite, : : : P ae 
Alpites 3 : : ; 3 2 
Fie. 9.—Part of a variole, showing calcite extending into its substance from a fissure 
of retreat. 
This would give us the sum total of molecules (SiO,).,, (Al,Os)<, 
(Fe,0;), FeO, (CaO),, (MgO), (Na,O),, a very close approximation 
to the result obtained by analysis, the water, as subsequently 
acquired, being disregarded. Since, however, silica has certainly 
been removed in solution, we must add sufficient of this to convert 
some of the olivine, and probably some of the magnetite also, into 
augite, which was evidently an original constituent of the rock. 
Probably: some of the calcium also was present in the form of 
pyroxene. | 
