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the stratification which they accompany, rarely 

 maintain that position for any considerable space. 

 In some part of their course they will be found to 

 become oblique, so as to touch more than one 

 stratum of a series ; or to intersect it at a consi- 

 derable angle, or to detach ramifying veins through 

 it. These are the cases in which the accompa- 

 ny ing strata are so frequently bent, contorted, and 

 fractured ; often to such a degree as to be mixed 

 in a confused manner with the veins. Fracture 

 and confusion of the neighbouring strata, thus 

 also become criteria by which a vein may be dis- 

 tinguished from a stratum. 



In cases of this nature, veins of a simple rock 

 sometimes contain imbedded fragments of the 

 strata which they traverse. ' Such fragments are 

 sometimes unaltered; at. others, they are much 

 changed in aspect, and graduate into the matter 

 of the vein. 



Veins, like pseudo-strata, are limited to the 

 rocks of the overlying family, or to the traps, sy- 

 enites, and porphyries, and to granite; and, as in 

 that case, it is here presumed, on grounds of 

 which the reasons cannot J>e stated here, that all 



