354 ON THE APPARENT DISLOCATIONS [Ch. XV. 



four parts, by transverse fractures, which have again united 

 without the intervention of any intermediate substance. Pre- 

 vious to this reunion, however, they have been slightly shifted, 

 in such a way that the several parts of the fractures project, 

 and the whole crystal has undergone a slight deviation from 

 its original straight line. If it be alleged that this appear- 

 ance could arise from a disturbed crystallisation, the next 

 specimens will remove any doubt on this head. In these, 

 the crystals have not only been fractured in the same way, 

 across their axes, but the fractures are filled by the quartz 

 and felspar, which constitute the body of the rock. The 

 granite-veins of Arran do not show more clearly the ramifica- 

 tion of a central substance through the fractures of the 

 neighbouring rock, than these specimens show the veins of 

 quartz proceeding from the mass, and penetrating every 

 fissure which had been formed in the crystal. It is perfectly 

 evident that whatever is true of the above cited granite-veins 

 must also be true of this rock, that the shorl has been crys- 

 tallised, then broken, and penetrated by quartz in a state of 

 fluidity. Nor is there any intermixture of the matter of 

 quartz with the matter of shorl, but the line of separation is 

 most accurately drawn between them. It follows then from 

 these circumstances, that the rock in question is not a simul- 

 taneous formation from a state of fusion, nor can we readily 

 understand how it can be the effect of fusion at all, con- 

 sistently with the chemical principles we acknowledge. Had 

 such a mass of fused quartz invaded the minute fragments of 

 shorl which the specimen exhibits, the latter must either have 

 been formed into a shapeless mass, or at least the asperities 

 of fracture could not have remained in a substance whose 

 fusibility is so much lower than that of quartz. To those 

 who attribute the formation of this rock to aqueous solution, 

 it may be objected that the crystals of shorl are sometimes 

 bent without fracture, so as to form considerable curvatures. 

 The noted fragility of shorl will not allow us to suppose that 

 it could be bent without breaking, unless it had been pre- 



