288 



FLAT VEINS AND PIPE VEINS. 



down to its present depth of two hundred and ten fathoms fronfi the 

 surface. It ought, however, to be added, that some portion of tin 

 was found in different parts of the vein, which may therefore be said 

 to have prevailed more or less from the surface to the present work- 

 ings.'?* 



The thickness of veins, and the quantity and quality of the ore they 

 contain, vary in every mine. Some veins are only a few inches 

 wide ; others are several feet, and sometimes several yards, in width. 

 Veins are often narrow in one part, and swell out in another. The 

 vein at the Dolcoath mine in Cornwall, varies from two or three feet 

 to forty feet ; and in some places it contracts to litde more than six 

 inches. The veinstone is quartz, in which are imbedded masses 

 called bunches of copper pyrites, consisting of copper combined with 

 sulphur and iron. 



Beside rake veins, there are other mineral repositories, called flat 

 veins, or flat works, and pipe veins. In some instances, a rake vein 

 declines from its regular inclination, takes the direction of the beds 

 of rock, running between them for a greater or less extent, and then 

 resumes its former inclination. In other instances, the cavities be- 

 tween beds or strata, are filled with metallic ores, lying between an 

 upper and lower stratum, like a seam of coal, and are subject to sim- 

 ilar dislocations : but these are not regular strata ; they may, fre- 

 quently, be traced to a perpendicular or rake vein, from which they 

 appear to be lateral expansions ; see Plate VII. fig. 2., in which the 

 regular vein is seen descending, and the flat vein branching off on 

 each side near the bottom. 



There is, generally, what is called a rider, or mass of mineral mat- 

 ter, between the ore of very strong rake veins, and that in the flat 

 veins, at the place of junction. The flat veins that run parallel be- 

 tween the strata, frequently open into large cavities filled with ore 

 and veinstone ; these cavities close again by the contracdng, or what 

 the miners call twitching of the sides, by which the ore is nearly or 

 totally excluded. Such expansions and twitchings are also common 

 to rake veins, as represented at c c, Plate IV. fig. 4. 



The blue john, or fluor spar mine, near Castleton, is of this kind. 

 The vein which contains this spar is separated from the limestone 

 rock by a lining of cawk or sulphate of barytes, and by a thin layer 

 of unctuous clay ; it swells out into large cavides, which contract 

 again, and entirely exclude the ore, leaving nothing but the hning of 

 the vein to conduct the miner to another repository of the spar. The 

 crystallizations and mineral incrustations on the roof and sides of the 

 natural caverns which are passed through in this mine, far exceed in 

 beauty those of any other cavern in England ; and were the descrip- 

 tions of the Grotto of Antiparos translated into the simple language of 



* Transactions of the Geological Society, vol. ii. 



