Yol. 52.] BASALT-PLATEAUX OF NORTH-WESETRN EUROPE. 371 



carry seaward the drainage of the districts of Morar, Arisaig, or 

 Moidart. 



AYhen one scans the great precipice on the western side of the 

 island of Eigg, which displays a transverse section across the 

 pitchstone-lava with its buried river-bed and the basalt-plateau 

 underneath, there seems no chance of any further westward trace 

 of this pitchstone being ever found. The truncated end of the 

 Scuir looks from the top of the cliff out to sea, and the progress of 

 denudation might have been supposed to have effectually destroyed 

 all evidence of the continuation of the rock in a westerly direction. 

 Some years ago, however, my friend Prof. Heddle, while cruising 

 among the Inner Hebrides, landed upon the little uninhabited islet 

 of Hysgeir, which rises out of the open sea, some 18 miles to the 

 westward of Eigg. He at once recognized the identity of the rock 

 composing this islet with that of the Scuir, and in the year 1892 

 published a brief account of this interesting discovery. 1 



I have myself been able to land on Hysgeir in two successive 

 summers, and can entirely confirm Prof. Heddle' s identification. 

 The islet stands on the eastern edge of the submarine ridge which, 

 running in a north-easterly direction, culminates in the island of 

 Canna. Hysgeir is a mere reef or skerry, of which the top rises 

 only 38 feet above the Ordnance datum-level. Its surface is one of 

 bare rock, save where a short but luxuriant growth of grasses has 

 found root on the higher parts of two or three of its ridges, and on 

 the old storm-beach of shingle which remains on the summit. The 

 rock undulates in long low swells that run in a general direction 

 20° to 45° west of north, and are separated by narrow channels or 

 hollows. The place is a favourite haunt of gulls, terns, eider-ducks, 

 and grey seals, and is used by the proprietor of Canna for the 

 occasional pasturage of sheep or cattle. So numerous are the 

 sea-fowl during the breeding-season that the geologist, intent upon 

 his own pursuits, may often tread unawares on their nests, while 

 he is the centre of a restless circle of white wings and anxious 

 cries. 



The pitchstone of Hysgeir, like that of Eigg, is columnar, the 

 columns being irregularly polygonal and varying from 3 to 10 

 inches in diameter. They are packed so close together that the 

 domes of rock on which their ends appear look like rounded masses 

 of honeycomb. They may here and there be observed to be 

 arranged radially, with their ends at right angles to the curved 

 exterior of the ridges, as if this external surface represented the 

 original form of the cooled pitchstone, and were not due to mere 

 denudation. There can be no doubt, however, that the island has 

 been well ice-worn. 



At the north-western promontory a beautiful example of fan- 

 shaped grouping of columns may be observed on a face of rock which 

 descends vertically into the sea. Here, too, is almost the only 

 section on which the sides of the columns may be examined, for, as 



1 Appendix C to ' A Vertebrate Fauna of Argyle and the Inner Hebridea,; 

 by J. A. Harvie-Brown and Thomas E. Buckley, p. 248. 



Q. J. G. S. No. 206. 2 c 



