illnstrative of Geology. 83 



has partly been formed, which appears here and there fused 

 and vesicuLir. Sandstone from the lowest stratum of the ma- 

 sonry over the frame of the blast furnace that was extinguished 

 in the year 1823 at Elend in the Harz, had not only received 

 a black, speckled appearance from the penetration of graphite 

 in vapour, that had deposited itself in the form of powder, but 

 even the originally solid mass was converted into thin undulat- 

 ing, easily separable beds. Such observations render it highly 

 probable that whole mountain masses have here and there gained 

 a different structure from the penetration of vapours. Is it not 

 probable that the oxide of iron, which penetrates mountain 

 masses in which layers of red ironstone are imbedded, may have 

 gained access to them in the form of vapour ? and, May not 

 the occurrence of the graphite which sometimes impregnates 

 whole mountain strata, and is found concentrated in particular 

 masses, be explicable by the circumstance just mentioned ? 



Certain metallurgic productions have likewise elucidated the 

 fact, that fused mountain masses which have forced their way 

 through others of an earlier creation might change later ones, 

 not only by the heat which they communicated, but even by 

 penetration. The penetration of litharge into the hearth of 

 the refining oven is sufficiently known, and presents nothing 

 striking, the mass being porous. We observe an occurrence 

 exactly analogous to this in a stream of lava, which, as it sweeps 

 along a loose surface, penetrates into the earth. More worthy 

 of note is the phenomenon which I remarked on pieces of the 

 forepart of the building of an extinguished blast-furnace at the 

 Steinrennerhiitte, in the Harz. Veins of a silicate of the black 

 oxide of iron, resembling slags of the refining process, cross in dif- 

 ferent directions the sandstone changed by the heat. The veins 

 which ramify towards the sides are of different sizes, extending 

 perhaps to half an inch, and have evidently ensued from the 

 penetration of fused masses into the fissures of the sandstone. 

 Here and there are vesicular cavities which appear partly lined 

 with crystals of that silicate. The sandstone is, on the whole, 

 loose, but becomes gradually more solid and altered as it ap- 

 proaches the veins. The immediate boundary of the vein forms 

 a solid mass of an altered appearance, and of a greenish-grey 

 colour, varying in extent from the width of a few lines to the 

 F 2 



