94 Mr HAIDINGER on the Parasitic Formation 



chiefly on a belief, that blende is changed into lead-glance. We 

 are not entitled by observation to admit of such a change ; and 

 though in this manner it does not appear that we can come too 

 soon with our mining operations, we see plainly that at least, as 

 at Lead-hills, we may come too late ; for that vein which now 

 contains the carbonates, and sulphates, and phosphates, must have 

 been once replete with the much more valuable sulphuret of 

 lead. Evidently, also, those among the Freiberg veins have been 

 opened too late, which now are found to contain the large six- 

 sided prisms of iron-pyrites, produced by the decomposition of 

 that valuable ore, the brittle silver, or prismatic melane-glance of 

 MOHS ; this, at least, is the only species to which we can attri- 

 bute the shape of those prisms, although they themselves remain 

 in some measure problematical. 



The changes are not at an end, even with the complete 

 destruction of the sulphuret. I must in particular mention 

 three cases, all of them in specimens from Lead-hills, in the 

 cabinet of Mr ALLAN, in support of this observation. One 

 of them has distinctly the form of large, perfectly recogniz- 

 able crystals, with a rough surface, however, of the prisma- 

 tic lead-baryte. The whole of the substance of the crystals 

 is a granular tissue of minute crystals of the di-prismatic 

 lead-baryte. The sulphate, Pb S 2 , containing 73.56 per cent, 

 oxide of lead, has been here converted into carbonate, Pb C 8 , 

 which contains 83.52 per cent, of the same ingredient. The 

 form in the second case is that of the low six-sided prisms of the 

 axotomous lead-baryte, with pretty smooth surfaces. Its sub- 

 stance is an aggregated mass of crystals, likewise of the di-pris- 

 matic lead-baryte, but presenting in their distribution much re- 

 semblance to the mode in which the individuals of malachite are 

 arranged, which replace the crystals of the blue copper. The sul- 

 phato-tri-carbonate has here given way to the carbonate of lead. 

 The third specimen, like the preceding one, has the form of the 



