Mr William Stevenson on the Origin of Granite. 167 



Clachich, several beds of highly metamorphic quartz rock 

 are seen, with the same dip. Porphyry (red felspar) is very 

 frequent, traversing the schists in conformable veins, or in- 

 tersecting them at various angles. Within the glen proper, 

 a beautiful massive granite, composed of white quartz, red 

 felsjjar, and black mica, is seen in the bed of the Cona. Its 

 divisional planes are vertical, W.N.W. to E.S.E. It here 

 encloses portions of what seem to be fragments of schist 

 melted down. These are of a dark hue, approaching black. 

 A few yards further up, the granite is divided by cross 

 fissures, the divisional planes here being W.N.W. by N.N.E. 

 Just above this place, the granite resembles a trap tuff. It 

 contains fragments of schists and quartz rock, much altered, 

 in great abundance. The fusion here has not, however, been 

 complete. Above this, the transition of the schists into the 

 granite is well seen. The strata have been melted in situ, 

 retaining their planes of stratification as principal cleavages. 

 Where the fusion has been imperfect, the result is a kind of 

 gneiss. Some very beautiful beds of granitoidal schist are 

 here seen. The adjoining strata consist of laminae of clay 

 and mica slates, alternating with very thin layers of granular 

 quartz. Near the granite and porphyry, where the meta- 

 morphism becomes extreme, flesh-coloured felspar is added, 

 chiefly between the slaty and quartzose laminae. It appears 

 to have been introduced into the schists rather by a process 

 of molecular transference whilst the beds were softened by 

 the intense heat of the adjacent molten matter, than by 

 simple injection in a melted state into open crevices between 

 the laminae. At this interesting spot, within the space of a 

 few yards, are to be seen granite, porphyry, quartz rock, 

 micaceous clay slate, a sort of hornblende schist, gneiss (the 

 result of the addition of felspar to the quartzose schists above 

 described), and a great variety of mixtures of all these, the 

 result of their total or partial fusion. The porphyry here 

 is of the common flesh-red colour, but is harder than usual, 

 owing to its containing a considerable admixture of quartz, 

 evidently derived from the quartzoso strata through which 

 it has been erupted. It also contains a little black mica i 

 and, in fact, might technically be with propriety termed a 



