224 Professor Gustav Bischof on the 



narrow mass, however liquid it may have been, must have 

 become solidified soon after its entrance into the cleft. E very- 

 hypothesis, however, must be rejected as untenable which 

 does not equally and satisfactorily explain the filling both 

 of narrow and of wide vein-fissures. Further, as the rising 

 of melted masses must have been as often repeated as more 

 space was afforded by the continued widening of the cleft, 

 it would be necessary to assume that during this widening 

 the force which sent up the mass was in a constant state of 

 activity. It is true that there is no difficulty in assuming 

 this to have been the case ; but undoubtedly it must have 

 happened that during the gradual widening of the cleft the 

 melted mass must have endeavoured to rise, and have become 

 solidified half way, thus closing up the exit for ever. We 

 ought, therefore, to find frequent examples of metalliferous 

 veins only partially filled. Unfilled clefts proceeding from 

 the surface to unknown depths, and easily distinguished from 

 the not unfrequent drusy cavities, ought to be abundantly 

 met with. 



With regard to the separation of fragments from the ad- 

 joining rock, in consequence of the continued splitting and 

 widening of the original fissure, it is true that their becoming 

 enveloped by vein-masses would take place just as well as by 

 means of precipitation from watery liquids, in the same man- 

 ner as this is exhibited by veins which are filled with crystal- 

 line mountain rocks. All such fragments must appear altered 

 in quite a different manner from the state in which we find 

 them in metalliferous veins ; not decomposed and disinte- 

 grated, but hardened, and rendered more compact by means of 

 the heat ; nay, even if they were neptunian products, as for 

 example, clay-slate, of crystalline structure, in consequence of 

 gradual cooling. An interruption in the regular sequence of the 

 several portions of the vein, and the occurrence of the newer 

 portions at the broken-up parts of the vein, would not be 

 comprehensible on the supposition of the filling of the vein- 

 fissures in the igneous way. If we could even assume that 

 uniformly constituted stripes and layers were separated 

 from the melted mass during its cooling, the same must 

 have occurred, and in a similar order, in the vein-mass which 

 was subsequently introduced ; unless the vein-mass had be- 



