I 



On Mineral and Metallic Veins, 487 



our readers to this interesting branch of geology, we must refer 

 them to scientific works for further details, having a great deal 

 to suggest on the direction of veins, and their intersection and 

 consequent shifting, as well as to illustrate them under these cir- 

 cumstances, as they present themselves to miners, by some figures. 



As a system of veins maintaining a general parallelism, is of- 

 ten intersected by another set apparently belonging to another 

 system, it is to be inferred that the veins thus intersected and 

 divided, preceded those which intersect them, as to time. It is 

 also to be observed, that mineral veins are all either vertical or 

 highly inclined, and that their lowest portions are generally 

 the thickest ; it is true that some appear to be horizontal, a 

 fact which appears opposed to the inference that their source is 

 from below, and which has induced many, who perceived the 

 impossibility of their being produced by aqueous deposits, to sup- 

 pose that they were all the results of crystallization. Hori- 

 zontal veins, however, have, in such numerous cases, been dis- 

 covered to be mere ramifications of larger ones that are either 

 vertical or highly inclined, that those whose horizontal direction 

 cannot be traced to them, may nevertheless be referred for their 

 origin to an inferior source ; and there can be no reasonable 

 doubt that it would be found to be so, if their roots could be 

 laid bare, which in many cases can only be by deep excavations ; 

 and the deeper we go, the less we find of this horizontality. 



We shall stop to illustrate this subject by referring our rea- 

 ders to fig. 1, of plate xiii. where there is a very instructive 

 view of a system of trap veins intruding into sandstone, on the 

 east coast of Trotternish in the Isle of Sky in Scotland. Trap, it 

 is true, occurs in such vast masses, and forms occasionally rocky 

 districts of such great extent, that it may be thought by some 

 not to be a proper subject for the illustration of what are strictly 

 mineral veins. The consideration of trap rocks, it is true, be- 

 longs to a different branch of the subject, but we consider that 

 no truth is more universally acknowledged in geology, than that 

 volcanic lavas, ancient traps, with other intrusive rocks, and 

 many of the veins of which we are now treating, are all the re- 

 sult of the expansive power which is eternally striving in the 

 central parts of the earth, and that the phenomena of mineral 

 veins may be truly illustrated by trap veins. 



In this interesting section of Trotternish, which is taken from 



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