108 Mr HAIDINGER on the Parasitic Formation 



the same colour as the rest, dividing it into two, without pro- 

 ducing the least deviation in the faces of cleavage upon which it 

 is seen. This line is evidently the section of the original sur- 

 face of the pyramid of calcareous spar, upon which one por- 

 tion of the brown-spar was deposited, while another portion 

 was formed within the space previously occupied by the calca- 

 reous spar, and destroyed in the progress of decomposition. 

 The chemical change is here very distinctly indicated ; part 

 of the carbonate of lime is replaced by carbonate of magnesia, 

 so as to form in the new species a compound of one atom of 

 each. How this change was brought about, is a difficult ques- 

 tion to resolve, though the fact cannot be doubted, as we have 

 in the specimen described a demonstration of it, approaching in 

 certainty almost to ocular evidence. It is scarcely surprising, 

 that such appearances should be visible in metallic veins, like 

 some of those near Schemnitz in Hungary, the whole nature of 

 which shews that they must have been gradually changed by 

 successive revolutions, the uppermost part being often almost 

 entirely composed of cellular quartz, which is formed in fis- 

 sures contained in other species or compound masses, subse- 

 quently decomposed, and leaving the quartz alone. I shall not 

 enter into an inquiry respecting the probability of such changes 

 in mountain masses, of such an enormous bulk as the dolomite of 

 the Tyrol, to which VON BUCK ascribed a similar origin. The 

 facts observed on a small scale, do not exclude the possibility of 

 such changes, though we are certainly less prepared to expect 

 them, where powerful and momentary revolutions are supposed 

 to have taken place at the same time, than where any period of 

 time, even the most protracted, may be granted for the succes- 

 sive replacement of one particle of matter by another. 



Crystals of calcareous spar, previously coated with smaU indi- 

 viduals of quartz, often entirely disappear, and leave an empty 

 shell. We sometimes observe particles of the calcareous spar 



