Metalliferous Veins. 153 



Before, however (he continued), we proceed to inquire into 

 the origin of mineral veins, it may not be out of place to inquire 

 " what a mineral vein is?" 



" Veins or lodes," says Mr Burr, " must be understood to be 

 the contents of what have been originally cracks Q* fissures, tra- 

 versing rocks longitudinally, and descending into them at various 

 angles with the horizon, but usually much inclined." 



Mr Carne says, " By a true vein, I understand the mineral 

 contents of a vertical or inclined fissure, nearly straight, and of 

 indefinite length and depth. These contents are generally, but 

 not always, different from the strata, or the rocks which the 

 vein intersects. True veins have usually regular walls, and 

 sometimes a thin layer of clay, between the wall and the vein ; 

 small branches are also frequently found to diverge from them 

 on both sides. Contemporaneous veins have been usually dis- 

 tinguished from true veins by their shortness, crookedness, and 

 irregularity of size, as well as by the similarity of the constitu- 

 ent parts of the substances which they contain, to those of the 

 adjoining rocks, with which they are generally so closely connect- 

 ed, as to appear a part of the same mass. When these veins 

 meet each other in a cross direction, they do not exhibit the 

 heaves or interruptions of true veins, but usually unite. When 

 they meet true veins they are always traversed by them." 



Mr Burr remarks, " Contemporaneous veins, or veins of se- 

 gregation, which appear to have resulted from a chemical se- 

 paration of certain mineral and metallic particles from the mass 

 of the enclosing rocks, while yet in a soft or fluid state, and the 

 determination of these particles to particular local situations. 



Playfair, the great illustrator of the Huttonian theory, ob- 

 serves, " veins are of various kinds, and may in general be defined 

 separations in the continuity of a rock of a determinate width, 

 but extending indefinitely in length and depth, and filled with 

 mineral substances different from the rock itself. The mineral 

 veins, strictly so called, are those filled with sparry or crystal- 

 lized substances, and containing the metallic ores." 



Werner defines veins to be " particular mineral repositories 

 of a flat or tabular shape, which in general traverse the strata of 

 mountains, and are filled with mineral matter, differing more or 

 less from the nature of the rocks in which they occur." He 



