CHAPTER XLIV 
THE BOSSES AND SHEETS OF GABBRO IN THE DISTRICTS OF RUM, ARDNA- 
MURCHAN, MULL, ST. KILDA AND NORTH-EAST IRELAND. HISTORY OF THE 
GABBRO INTRUSIONS 
2. The Island of Rum 
The mountains of the island of Rum, rising as they do from a wide expanse 
of open sea, present one of the most prominent and picturesque outlines in 
the West Highlands (Map VI.). More inaccessible than most of the other 
parts of the volcanic region, they have been less visited by geologists. They 
were described by Maceulloch as composed of varieties of “ augite rock.” He 
noticed in this rock “a tendency to the same obscurely bedded disposition 
as is observed in other rocks of the trap family,” and found at one place that 
it assumed “a regularly bedded form, being disposed in thin horizontal 
strata, among which are interposed equally thin beds of a rock resembling 
basalt in its general characters.” 1 Professor J udd repeats Maceulloeh’s 
observation, that “ the great masses of gabbro in Rum often exhibit that 
pseudo-stratification so often observed in igneous rocks.” He regards these 
masses, like those of Skye and Mull, as representing the core of a volcano 
from which the superficial discharges have been entirely removed, and he 
gives a section of the island in which the gabbro is represented as an amor- 
phous boss sending veins into a surrounding mass of granite. 2 In a subse- 
quent paper he gave an excellent detailed account of the mineralogical 
composition of some of the remarkably varied and beautiful basic rocks 
constituting the hills of Rum, but added no further information regarding 
the geological structure of the island. 3 
Even from a distance of eight or ten miles, the hills of Rum are seen to 
be obviously built up of successive nearly horizontal tiers of rock. As the 
summer tourist is carried past the island, in that wonderful moving pano- 
rama revealed to him by the “ swift steamer ” of modern days, these great 
dark cones remind him of colossal pyramids, and as the ever-varying lights 
and shadows reveal more prominently the alternate nearly level bars of crag 
and stripes of slope, the resemblance to architectural forms stamps these hills 
with an individuality which strikes his imagination and fixes itself in his 
memory. If choice or chance should give him a nearer view of the scene, he 
1 Western Islands, i. p. 486. 2 Quart. Journ . Geol. Soc. xxx. p. 253. 
3 Op. cit. xli. (1885) p. 354. See also his paper in vol. xlii. of the same Journal. 
