186 Dr. Mac Culloch on Mineral Veins. 



sense, from east to west, and the more recent from north to 

 south. 



Their longitudinal extent must evidently be limited, but it is 

 often considerable. They have been traced for two, and even 

 three, miles, in Cornwall; and it is said that one vein, in South 

 America, has been ascertained to extend for 80 miles. 



It is easy to see, however, that in a case of this nature, the 

 union of some tendency to system, with a little inaccuracy, may 

 easily confound many veins together. Observations made in 

 such a spirit of extravagant generalization, must necessarily 

 excite distrust, when we advert to the comparative length and 

 breadth of such a supposed continuous fissure, and to all the 

 circumstances under which these must have been formed. 



The breadth of veins is extremely uncertain, varying from 

 less than an inch to many yards. The question of their depth 

 is more interesting, as it is believed by some to be indefinite : 

 it is at least said, that their depths have never been reached by 

 miners. If that were even true, it would not prove the truth of 

 an opinion so improbable, when we consider the circumstances 

 under which fissures must have been formed. When the sepa- 

 rated or dislocated strata preserve an accurate parallelism, the 

 same relative disposition must exist between the opposite sides 

 of the vein ; and we may thus, if we please, imagine it intermi- 

 nable. But if the including strata have lost their parallelism 

 after separation, it is evident that, under one modification of 

 this, they may, or rather must, come into contact in some part 

 of the series, and that the vein will therefore disappear. This 

 reasoning only takes a simple view of the consequences result- 

 ing from the appearances ; but if the hypothesis of some geolo- 

 "■ists should be admitted, which supposes that the materials of 

 veins were ejected from the depths of the earth, then indeed 

 they may be indefinite in their downward progress. But this is 

 pure speculation. 



The absolute antiquity of veins, in any situation, is a subject 

 respecting which no conjectures can be formed ; but there are 

 two modes of judging of their ages, within certain limits. It is 

 evident, in the first place, that they are all posterior to the in- 



