Western Isles of Scotland. 107 



a height of from 90 to 95 feet. At the extreme north end of the 

 island the platform is on the whole a few feet higher, say 97 feet 

 above high-water mark. At the west side of the central hill there 

 appears to be a higher fragment of platform at 110 feet, but this is 

 rather doubtful. 



The platform is everywhere remarkably ice-moulded. No striae 

 were observed, but from the aspect of the roches moutonnees it is 

 clear that the ice came from the N.E. or E.JST.E., an observation 

 agreeing with the trend of the striae in TJlva. 



L u n g a, the largest of the Treshnish Isles, has a still more 

 extensive platform, which occurs all round the island except for local 

 interruptions in one or two places. The lavas lie nearly horizontal 

 with a very gentle clip to the north. The platform at the north end 

 is controlled by the occurrence of a very massive lava bed some 80 or 

 100 feet thick. The inner angle at the ruined houses is just 100 feet 

 above high-water mark of spring tides. As the massive bed is 

 followed south along the east side of the island it rises steadily and 

 carries up the platform with it to a height of 110 feet or more. 

 Soon, however, the platform abandons the massive bed and starts 

 again to the south of Cruachan at a lower horizon in the lavas. 

 Here, as in the case of the Bac Mor, it is at a very low level, the 

 inner angle being only 80 or 85 feet above high-water mark of spring 

 tides, and the general level of the platform, which extends for three- 

 quarters of a mile to the southern extremity of the island, only 75 or 

 80 feet. At the extreme south end it appears to rise again to 85 feet. 

 Along the west side only irregular remnants are preserved. 



Along the north, east, and south of the island the platform is even 

 more remarkably ice-moulded than on the Bac Mor, so that there is 

 absolutely no doubt as to its preglacial age. The ice-motion was, as 

 before, from the N.E. or E.N.E., but no stria? were found. 



VI. Conclusion. 

 The continuity of the old cliff and platform along stretches of coast 

 many miles in extent, and the manner in which the latter maintains 

 a uniform level independently of, and often in spite of, the rock- 

 structure, are sufficient proof that we are dealing with an old shore- 

 line. The repeated ice-moulding of the surface, and above all the 

 superposition in some localities of large masses of boulder-clay, show 

 that the feature was in existence before the Great Ice Age. Its 

 development as a rock-platform is quite comparable with that of 

 the preglacial beach of Southern Britain, but a correlation between 

 the two would at present be very unsafe. The main obstacle is 

 of course the want of preservation of deposits in connexion with 

 the platform of the Western Isles. Even in the absence of these 

 it might be possible to correlate if we could be sure that these 

 old shorelines were the only ones of immediately preglacial age 

 in their respective districts. At present, however, we cannot be 

 sure that other platforms of marine erosion do not exist below sea- 

 level. Moreover, in the south of Colonsay and in Oronsay there 

 are vague indications, first pointed out by Mr. Bailey, of a possible 

 plain of marine erosion a little above the present sea-level. The 



