observed In some Metalliferous Veins. 273 



left 10 grains of residuum from a pint ; from Huel Unity 16 

 grains ; from one shaft of Poldice 19 grains; and from another 

 ' 92 grains from the same quantity. 



"The muriatic salts, especially of lime, were most abundant; 

 but in some instances I have detected common salt, particularly 

 in the water from the bottom of the United Mines, the Consoli- 

 dated Mines, Huel Unity, and Poldice. Out of the 92 grains 

 of residuum from the latter, as mentioned above, 24 grains 

 proved to be muriate of soda, 52 grains of the muriate of lime 

 and magnesia, and the remainder muriatic acid with iron and 

 sulphate of lime. The water from another part of the same 

 mine contained 5.5 grains of common salt. All these mines are 

 in killas, or primitive slate, and several miles distant from the 

 sea" (excepting Dolcoath and Huel Unity, which are worked 

 both in granite and slate). 



This terminates the brief notice of the geological features of 

 the district, and other subterranean phenomena which bear on 

 our investigations. 



The mode of experiment pursued was by pressing plates of 

 sheet copper, of about 18 or 20 inches long, and from 3 to 4 

 inches wide, closely against such portions of the metallic con- 

 tents of the vein as were thought proper for examination. To 

 each of these plates a copper wire of 0.05 inch in diameter was 

 connected by closely twisting it round ; the opposite ends of 

 each wire being connected in the usual manner with a galvano- 

 meter. In some cases but a few feet of wire were required to 

 connect the stations ; in others many (in one instance six hun- 

 dred) fathoms were employed. In many instances the points 

 were situated at the same depth, and on a continuous vein ; in 

 others, still at an uniform depth, and on the same vein, but on 

 opposite sides of a cross-course dislocating (heaving) the vein; 

 in some, too, the stations were at the same level but on different 

 veins ; whilst there were many occasions in which the same vein, 

 and others in which different veins at different depths, were con- 

 nected through the galvanometer. The experiments have been 

 made on metalliferous veins bearing E. and W., N. E. and 

 S. W., and N. and S. 



The results obtained were much the same, whatever were the 

 directions of the veins. In all those producing tin-ore alone, in 



