Origin of Quartz and Metalliferous Veins, 223 



contact of the liquid with the separated fragments and with 

 the exposed surfaces of the adjoining rock. In this manner 

 the fragments were gradually removed to the middle of the 

 vein, and the water afterwards deposited other constituents, 

 so that new portions of the vein were precipitated between 

 the fragments and the adjoining rock ; the previously exist- 

 ing arrangements being thus disturbed. We can thus un- 

 derstand, how at one point in the same vein, where the 

 adjoining rock presented greater resistance to the formation 

 of the new fissure than the substance of the vein did, the new 

 portions of the vein were deposited in the latter ; whereas 

 in the reverse case, to which we have already alluded, these 

 new portions of the vein were introduced between the newly 

 formed walls. Hence the homogeneous stripes and layers 

 of a vein do not always present a similar succession in a 

 horizontal section proceeding from the walls to the centre. 



Were we to proceed on the hypothesis that the vein-masses 

 were introduced into the clefts in a fused condition, it would 

 be very difficult, nay impossible, to explain the phenomena 

 of metalliferous veins of which we have now spoken. This 

 hypothesis takes for granted, in the first place, that the 

 clefts, previous to their being filled, possessed such a width 

 that a fused mass could ascend in them without becoming 

 solidified in consequence of the cooling action of the walls 

 of the adjoining rock. To this, however, we find opposed 

 the consideration, that a wide fissure can only be supposed 

 to have remained open when it was quite perpendicular, but 

 not when it was more or less inclined; for in the latter 

 case it must have fallen together previous to its being filled. 

 It can be supposed that the fused mass which penetrated 

 with great force into a cleft only open from above, pushed 

 asunder the side walls, and thus increased the width between 

 them ; a case which undoubtedly occurred with regard to 

 the filling of clefts by crystalline rocks, as for example, in 

 the formation of veins of granite, porphyry, basalt, &c. Such 

 a process can only be imagined in regard to the larger 

 metalliferous veins, and not at all with respect to those hav- 

 ing a breadth of only a few inches, or only an eighth of an 

 inch ; because in the latter, as has already been remarked, a 



