CHAP. XLIV 
HISTORY OF THE GABBRO INTRUSIONS 
361 
platform of older rocks into the thick mass of the basalt-plateaux, successive 
sheets of dolerite and gabbro were forced outward between the layers of basalt. 
This took place all round the orifices of supply, on many different horizons, and 
doubtless at many different times. In some cases, the intrusive sheets were 
injected into the very bottom of the basalts, and even between these rocks 
and the older surface on which they rested. This is particularly the case 
in Bum, where the gabbro-cones spring almost directly from the ancient 
grits, schists and sandstones on which they rest. The intrusive sheets have 
likewise found egress at every higher platform in the basalt-series, up at 
least to the base of the “ pale group ” in Mull — that is, through a continuous 
pile of more than 2000 feet of bedded basalt. But the intrusion did not 
proceed equally all round an orifice. At all events, the progress of denuda- 
tion has revealed that on one side of a gabbro area the injected portions 
may occur on a lower stratigraphical level than they do on the opposite side. 
At the Cuillin Hills, for example, the visible sheets of dolerite and gabbro 
to the north of Coire 11 a Creiche begin about 1600 feet above the sea, which 
must be much more than that distance above the bottom of the basalts. On 
the south-east side, however, they come down to near the base of the basalts 
at Loch Scavaig ; that is to say, their lowest members lie at least 1600 
feet below those on the opposite margin. 
7. The uprise of so much igneous material in one or more funnels, 
and its injection between the beds of plateau-basalt, would necessarily 
elevate the surface of the ground immediately above, even if we believe that 
surface to have been eventually disrupted and superficial discharges to have 
been established. If no disruption took place, then the ground would prob- 
ably be upraised into a smooth dome, the older lavas being bent up over 
the cone of injected gabbro until the portion of the plateau so pushed upward 
had risen some hundreds of feet above the surrounding country. The amount 
of elevation, which would of course be greatest at the centre of the dome, 
might be far from equable all round, one side being pushed up further or 
with a steeper slope than another side. But even in the case of the Cuillin 
Hill area, it is conceivable that the total uplift produced at the surface a 
gentle inclination of no more than 8° or 10“. 
It is along the periphery of a gabbro area that we may most hopefully 
search for traces of this uplift. But unfortunately it is just there that the 
work of denudation has been most destructive. There appears also to have 
been a general tendency to sagging subsequent to the gabbro protrusions, 
and the inward dip thereby produced has probably been instrumental in 
effacing at least the more gentle outward inclinations caused by the uprise 
of the eruptive rock. In one striking locality, however, to which I have 
already referred, the effects of both movements are, I think, preserved. The 
basalt -plateau of Strathaird, which in its southern portion exhibits the 
ordinary nearly level bedding, dips in its northern part at an unusually 
steep angle to the north-west, towards the gabbro mass of Blath Blieinn. But 
before reaching that mountain the basalts, much interbanded with sheets of 
dolerite and gabbro, suddenly bend up to form the prominent eminence of An 
