8 



Romans in this part of Spain, seems to show that at some former epoch 

 the decomposition of metallic sulphides, and the formation of carbon- 

 ates, must have taken place under very favourable conditions. That 

 the change still goes on, is perfectly shown by specimens of brown fer- 

 ruginous blende from the mines of St. Felix and St. Lucita, near Co- 

 millas; in these specimens the decomposition of the blende into friable 

 earthy carbonate has proceeded regularly from without inwards, most 

 specimens still containing a nucleus of unaltered blende. 



The calcedonous yellow and white Smithsonite already spoken of, 

 and which is so abundantly found at the Merodio mines, near Comillas, 

 in reniform and botryoidal masses, must have been deposited from 

 solution. This opinion is corroborated by the circumstance that, in the 

 same mine, the calcite vein stone enclosing blende, has been in great 

 part substituted by carbonate of zinc. One of the resulting pseudomor- 

 phites has the form of the scalenohedron, called by Haiiy the metasta- 

 tique; and although not quite half a complete form, the terminal edges, 

 which are well defined, are nine centimetres long. It is a shell of from 

 3 to 5™™ thick of semi-translucent Smithsonite, which is partially filled 

 up with a warty tufaceous mass of the same substance. The inner side 

 of the shell, in the part not filled up, is covered with a number of small 

 warts. "Whenever one of these more or less hollow pyramids is unbroken, 

 a small hole may be observed in the end, where it is broken off from 

 the wall of the druse ; through this the lime was removed, and the 

 tufaceous zinc introduced. A similar hole may often be seen in large 

 crystals of felspar, which have been decomposed in the inside, or in a 

 tooth in the first stage of decay. 



This association of compounds of iron with those of zinc is in- 

 teresting, especiall}^ in connexion with the minerals which form the 

 subject of this paper. In the capping of dolomite forming the south 

 side of the valley of Ciguenza, which has been formed by the re- 

 moval of the dolomite, and the laying bare of the underlying lime- 

 stone by denudation, occur several lodes, to which allusion has been 

 already made. One of these has been worked for galeniferous carbo- 

 nate at a mine called Emilia," while at another mine called " Yi- 

 centa," to the westward upon the same lode, the ore found was almost 

 pure carbonate. Upon sinking a mine in one of the parallel lodes about 

 30™ north of the principal lode at Emilia, only iron ore similar in appear- 

 ance to the calamine was found ; at the depth of five or six metres this 

 passed into pyrites, but blende was not found. The continuation of the 

 same lode to the westward, near the mine Yicenta, gave, on the other 

 hand, an earthy ore of iron mixed with blende, and at a greater depth 

 pyrites, — the ore consisting at this point of a rib, one side of which was 

 pyrites and the other blende. Still deeper the iron disappeared, and 

 was replaced by carbonate of zinc, exactly as in the neighbouring part 

 of the main lode. 



It would thus appear that the iron ore is the result of the decom- 

 position of pyrites. In this case, a large quantity of sulphuric acid must 

 have been formed and removed, and must have contributed to the de- 



