Ch. XV.] OF THE PRIMARY ROCKS. 359 



we repeat that they do sometimes terminate ; and although 

 the miner often finds that veins which have tapered away into 

 a mere string again expand into their original dimensions, 

 yet they are not always worked to this conclusion ; for, if they 

 continue very small for some distance, they are generally 

 abandoned : and that they are not of indefinite length may 

 be inferred from the fact that the continuations of profitable 

 veins, belonging to adjacent mines, have been sought for in 

 vain within the limits of probable dislocations. Indeed, if 

 veins were of this indefinite length, mining speculations would 

 not be so precarious. If the term indefinite means any thing, 

 true veins have no terminations : we will not, however, lay 

 much stress on this point; and, perhaps, it was only meant 

 to express that the extent of the length and depth has not 

 been ascertained. 



Again, it is said that veins were originally fissures; first, 

 on account of the resemblance in their forms ; and, secondly, 

 because they contain mechanical deposits such as have been ob- 

 served in actual fissures, now communicating with the surface. 

 The noted case of Relistian mine has been often adduced as 

 a proof of the latter ; but we have already attempted to show 

 that the masses of conglomerate enclosed in the lode are not 

 of a fragmentary nature, but owe their peculiar appearance 

 to a particular structure, not uncommon to some rocks, and 

 which is participated in by a chlorite-schist in the vicinity of 

 the lode. As regards the resemblance between the form of 

 veins and fissures, this cannot be considered conclusive ; if so, 

 the spaces occupied by the small elongated portions of slate 

 were also once fissures, as indeed even the strata themselves, 

 for they might be equally compared with chasms such as are 

 produced by earthquakes. On the supposition that veins 

 were originally fissures, Cornwall must have been subject to 

 innumerable convulsions : and in some districts, the total 

 thickness of these openings must have borne no inconsider- 

 able proportion to the whole mass. In St. Just, for instance, 

 within a single mile, how numerous the parallel lodes are 



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