382 
THE TERTIARY VOLCANOES 
BOOK VIII 
bars were actually dykes until I had crossed the valley and climbed the 
slopes of the hill . 1 
Good evidence of successive protrusions of the acid rock within 
the great area of the Bed Hills may be found on the south side of 
Meall Hearg at the head of Glen Sligachan, where the granophyre is tra- 
versed by a younger hand or dyke of fine-grained spherulitic material about 
ten feet broad. The rock exhibits there the same beautiful How-structure 
with rows of spherulites as is to be seen along the contact of the main grano- 
phyre mass with the gabbro.on the same hill, which will be afterwards de- 
scribed. This dyke, vein or band, though possibly belonging to the same 
epoch of protrusion as the surrounding granophyre, must obviously be later 
than the consolidation of the rock which it traverses. 
Occasionally round the margin of the granophyre a singular breceiated 
structure is to be seen. I have found it well marked on weathered 
faces, along the flanks of Glamaig and of Marsco, and Mr. Harker has 
observed many examples of it on the north side of the granophyre mass of 
the Bed Hills. When the rock is broken open, it is less easy to detect the 
angular and subangular fragments from the surrounding matrix, which is 
finely crystalline or felsitic. 
The actual junction of the eruptive mass with the surrounding rocks 
through which it has ascended is generally a nearly vertical boundary, but 
the granophyre sometimes plunges at a greater or less angle under the rocks 
that lie against or upon it. On the north side of Glamaig, for instance, 
the prophyritic and felsitic margin of the great body of eruptive rock de- 
scends as a steeply inclined wall, against which the red sandstones and marls 
at the base of the Secondary formations are sharply tilted. On the south 
side of the area a similar steep face of fine-grained rock forms the edge of 
the granophyre of the great southern cones, and plunges down behind Lias 
limestone and shale, Cambrian limestone and quartzite, or portions of the 
Tertiary volcanic series. Where the granophyre cuts vertically through the 
gabbro, the latter rock being more durable is apt to rise above the more de- 
composable granophyre as a crag or wall, and thus the deceptive appearance 
arises of the basic overlying the acid rock. As above mentioned, there seems 
every reason to believe that this peculiarity of weathering has given rise to or con- 
firmed the mistaken impression that the granophyre is older than the gabbro. 
There can be no doubt, however, that along many parts of the boundary- 
line the acid eruptive mass extends underneath the surface far beyond the 
actual base of the cones, for projecting knobs as well as veins and dykes 
of it rise up among the surrounding rocks. This is well seen along the 
northern toot of Beinn na Caillich. But of all the Skye bosses none ex- 
hibits its line of junction with the surrounding rocks so well and continu- 
ously as Beinn an Dubhaich. This isolated tract of eruptive material lies 
entirely within the area of the Cambrian limestone, and its actual contact 
1 The difference of contour and colour between the ordinary reddish smooth-sloped “ syenite” 
and the black craggy “ liypersthene rock "and “ greenstone ” in the Glamaig group of hills caught 
the eyes of Von Oeynhausen and Von Dechen (Karsten’s Archiv, i. p. 83). 
