Mr William Stevenson on the Origin of Granite. 167 
Olacliich, several beds of highly metaniorphic 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 
felspar, 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 tutf. 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 laminse. 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 laminee. 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 ; 
and, in fact, might technically be with propriety termed a 
