178 ON THE MINERAL AND METALLIFEROUS [Ch. IX. 



generally, they are separated by longitudinal seams, whilst the 

 cross seams of the slate often penetrate into the vein. 



At B, the vein is more regular, but is interesting as the 

 point at which the granitic elvan or vein comes in contact 

 with the lode, as shown in the general plan. 



Fig. 16. 



Part of Little Bound's Lode at B. 



This elvan consists of compact felspar which here and there 

 is porphyritic, and in some parts very micaceous; when it 

 approaches the vein it becomes quartzose, and gradually 

 passes into the vein, as it does also into the slate at many 

 points throughout its course ; and, what is particularly worthy 

 of remark, it terminates not far off in small veins and strings, 

 and at its other extremity, near the spot where the fishing 

 boats are drawn up, it becomes so blended and intermixed 

 with dark-coloured schistose rocks, that it is difficult to deter- 

 mine where the one begins and the other ends. 



By these examples we learn, that large metalliferous veins, 

 like the lesser ones which are confined to rock concretions, 

 though they may sometimes appear to have walls or way- 

 boards, yet these are not essentially necessary, being often 

 only found in certain parts of the veins, and may there- 

 fore be attributed to accidental circumstances, such as the 

 peculiar manner in which the substance of the lode was aggre- 

 gated ; the occurrence of a smaller vein of a different mineral 



