304 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 5, 



very different from those around it, in reality consists of two dis- 

 tinct varieties of rock, pitchstone and felstone-porphyry, arranged 

 in distinct and, in a general sense, horizontal beds. Looked at from 

 the east side (PI. XIV. fig. 1) this feature is not clearly marked ; 

 for the great cliff seems then to consist of one homogeneous mass, 

 except a marked columnar band running obliquely along the base of 

 the precipice. If, however, the side is viewed from the south, the 

 bedded character of its component rocks becomes a conspicuous fea- 

 ture. Along the noble cliffs on that side the two varieties of rock 

 are strongly distinguished by their contrasting colour and mode of 

 weathering, the sombre-hued pitchstone standing up in a huge pre- 

 cipice striped with columns, and barred horizontally with bands of 

 the pale-grey porphyry, which seems sunk into the face of the cliff. 

 At the south-east end of the ridge the beds are very distinct. 

 Further west of the precipices to the south of the Loch a Bhealaich, the 

 dark pitchstone which forms the main mass is divided by two long pa- 

 rallel intercalations of grey porphyry, and two other short lenticular 

 seams of the same material (see PI. XIV. figs. 2 & 3). It is clear from 

 these features, which are not seen by most travellers, who pass Eigg 

 merely in a steamer, that the Scur is in no sense of the word a dyke. 



But although the Scur is thus a bedded mass, the bedding is far 

 different from the regularity and parallelism of that which obtains 

 among the interbedded basalt-rocks below. Even where no interve- 

 ning porphyry occurs, the pitchstone can be recognized as made up of 

 many beds, each marked by the different angle at which its columns 

 lie. And when the porphyry does occur and forms so striking a 

 division in the pitchstone, its beds die out rapidly, appearing now 

 on one horizon, now on another, along the face of the cliffs, and 

 thickening and thinning abruptly in short distances along the line of 

 the same bed. Perhaps the best place for examining these features 

 is at the Bhealaich, the only gully practicable for ascent or descent, 

 at the south-eastern face of the ridge. 



By much the larger part of the mass of the Scur consists of pitch- 

 stone. As a rule this rock is columnar, the columns being much 

 slimmer and shorter than those of the basalt-rocks. They rise 

 sometimes vertically, and often obliquely, or project even horizon- 

 tally from the face of the cliff". They are seldom quite straight, 

 but have a wavy outline ; and when grouped in knoUs here and there 

 along the top of the tidge, they remind one of gigantic bunches of 

 some of the palaeozoic corals, such as Lithostrotion. In other cases 

 they slope out from a common centre, and show an arrangement not 

 very unlike that of a Highland peat- stack. 



The pitchstone of the Scur differs considerably in petrographical 

 character from any other of the pitchstones of the island, and indeed 

 from any other pitchstone which I have yet met with in Scotland. 

 Its base is of a velvet-black colour, and is so much less vitreous in 

 aspect than ordinary jjitchstoue as to have been described by Jameson 

 and later writers as intermediate between pitchstone and basalt*. 



* ' Mineralogy of the Scottish Isles,' vol. ii. p. 47. Sec also MaccuUoch, ' West- 

 ern Isles,' vol. i. p. 521, and Hay Cunningham, 'Mem.Wern.Soc' vol. viii. p. 155. 



