40 MR STEVENSON ON THE GEOLOGY OF COCKBURNLAW, 
examples are seen in this district, it seems not improbable that the syenite of 
Cockburnlaw and the Staneshiel is nothing more than greywacke, fused by the 
agency of the molten granite, and the mineral characters of the two rocks thereby 
blended together. The granite invariably assumes the aspect of syenite, as it ap- 
proaches the greywacke. At Cockburn Mill dam, the greywacke is considerably 
hardened, and dips to NNW. at high, but varying angles. Below the dam the 
hardness increases, the planes of stratification become less distinct, while those 
of cleavage grow more decided at every step. All these symptoms of meta- 
morphism increase as we approach the igneous rock, the texture of the greywacke 
being changed to crystalline, and the size of the crystals increasing with the hard- 
ness, until we arrive at a point, where it is impossible to decide from the appear- 
ances presented, whether the rock should be considered greywacke or syenite. Be- 
yond this, it graduates into true syenite, which is divided by cleavage planes into 
large rectangular blocks, arranged in the form of thick beds, having he same dip 
and strike as the adjoining greywacke. The cleavage planes which run parallel 
to those of the stratification of the greywacke (if, indeed, these are not merely 
the original planes of stratification of the rock before it was converted into syenite), 
are distinguished from those running at right angles thereto, by being occupied by 
veins of heavy-spar, associated with crystals of quartz. These veins run con- 
tinuously in a WSW. to ENE. direction. As we proceed further into the mass, 
the syenite becomes more crystalline, and passes by a regular and gradual transi- 
tion, into the well characterized granite of the Staneshiel. Two varieties of gra- 
nite are here seen intruding in the form of veins, which have evidently been 
poured, in a molten state, into fissures opened in the syenite, during the process 
of crystallization. One of these is a beautiful and regularly crystallized granite, 
larger in the grain than is commonly met with in the adjoining hills. The other 
is small grained, and rather soft, and seems to be connected with a dyke which 
occurs in the bed of the river a little above the dam, being identical in mineral 
character. This dyke can be traced, when the water is low, for about 200 yards. 
It is about five feet thick, and runs nearly NNW., but is frequently interrupted 
in its course by the greywacke which it crosses. It contains, in some places, 
fragments of the latter rock, which it has detached and brought up with it, in its 
passage through the strata. The adjoining strata have been partially fused, and 
present in some places a syenitic appearance. The alteration extends to a con- 
siderable distance from the dyke, the strata being extremely hard, and frequently 
exhibiting contorted laminee. In the immediate vicinity of the dyke the planes of 
stratification are very obscure, being, in many places, merely marked by veins of 
spar. Both the dyke and the adjoining metamorphic rocks are traversed by 
numerous veins of heavy-spar, together with a few of quartz. 
The summit of Cockburnlaw consists of beds of metamorphic greywacke, 
which dip to NW. at an angle of about 65°. The metamorphism of the strata 
increases as we approach the great body of granite, which lies immediately below 
