7 



domorphites of the calcite in the form of scalenohedrons. At the mines 

 which have been worked Dear Ciguenza, a village about five miles east 

 of Santander, the thickness of the lode is variable, increasing at the 

 points where ore, especially carbonate, occurs, to l™or 2™, but diminish- 

 ing to an inch where this mineral disappears, or is replaced by blende. 

 Sometimes all ore disappears, so that the lode is only represented by a 

 band of bar^^tes, or calcite. 



In the district just named, several lodes run east and west nearly 

 parallel, and can be traced over a length of about 1000™ in the dolomite, 

 beyond which, though doubtless they extend much further, it is difii- 

 cult to trace them, in consequence of the nature of the ground. Some 

 of the lodes consist of a rib of carbonate of zinc, sometimes galeniferous, 

 of varying thickness, encased in very light friable ochiy clay, looking 

 like decomposed dolomite. In others, the ore consists of carbonate and 

 blende, the latter forming the centre rib. 



The carbonate of zinc, or Smithsonite, found in these lodes, is generally 

 very cavernous, or rather what may be termed clinkery, the walls of the 

 empty spaces being frequently lined with small crystals of the same 

 mineral. The ore is usually yellowish-brown ; it is also found as a 

 yellowish- white compact mineral, resembling the dolomite in appearance, 

 in very dense calcedony-like semi-translucent masses of a pale yellow 

 colour, passing into white, the surfaces of which have a reniform struc- 

 ture, in stalactitic forms, and as a friable, and more or less compact earthy 

 mineral, associated with blende. The blende from the higher ranges, 

 such as the mountains of Europe, is comparatively free from iron, and is 

 frequently found of a sulphur -yellow, or pale garnet-red colour, and 

 beautifully transparent. This blende decomposes into pure white Smith- 

 sonite, which is sometimes compact and dense, and sometimes in friable 

 earthy masses ; when broken, some unaltered blende is often found in the 

 centre of pieces of this kind of carbonate. An earthy pale bulF-coloured 

 dolomitic-looking carbonate of zinc, associated with earthy cinnabar, is 

 found in the same locality ; this is obviously derived from a less pure 

 variety of blende, mixed with cinnabar, which occurs there. We also 

 meet with a granular crystalline form of Smithsonite, of a pure white 

 colour, or tinged with a pale lemon-yellow or rose. 



The blende occurring in the limestone, and especially that in the 

 dolomite, is ferruginous, and in some cases appears to decompose with 

 great facility into Smithsonite. 



When the blende from which the Smithsonite is derived is associated 

 with galena, the latter is very commonly found unaltered in the car- 

 bonate of zinc. It appears, however, to have sometimes undergone de- 

 composition ; for crystals of carbonate are found abundantly in Smith- 

 sonite from Puente Viesgo, from the Venta mine near Comillas, and 

 from the mines of Cells (three leagues south of San Yincente de la Bar- 

 quera), and no doubt would be found in all galeniferous Smithsonite 

 from the district. Specimens may often be found containing galena, 

 blende, and carbonates of lead and zinc. The existence of lodes of pure 

 white carbonate of lead, known to, and extensively worked by the 



