Mr. Campbell on the Glacial Phenomena of the Hebrides. 75 



mountain-region. After describing the characters presented by the 

 bottom-till in the northern part of Lewis, the author proceeded to 

 notice those of the lakes, some of which trend north-west and south- 

 east, others north-east and south-west, whilst those of the mountain 

 district follow no particular direction. The lake-basins of the first 

 series he regarded as formed at the same time and by the same 

 agency as the roches moutonnees and other marks of glacial action ; 

 they are true rock-basins or hollows between parallel banks formed 

 wholly of till, or of till and rock. The N.E. and S.W. lakes coin- 

 cide in direction precisely with the strike of the gneiss ; and the 

 author explained their origin by the deposition of till by the land-ice 

 in passing over the escarpments of the gneiss facing the north-west. 

 The lakes of the mountain district are regarded by the author as all 

 produced by glacial erosion. The author considered that the ice 

 which passed over the northern part of Lewis could only have come 

 from the mainland. Referring to the glaciation of Raasay, he 

 showed that the ice-sheet which effected it must have had in the 

 Inner Sound a depth of at least 2700 feet ; and taking this as ap- 

 proximately the thickness of the mer de glace which flowed into the 

 Minch, which is only between 50 and 60 fathoms in depth, no part 

 of this ice could have floated, and the mass must have pressed on 

 over the sea-bottom just as if it had been a land surface. Ice 

 coming from Sutherland must have prevented the flow of the Ross- 

 shire ice through the Minch into the North Atlantic, and forced it 

 over the low northern part of Lewis ; and the height to which Lewis 

 has been glaciated seems to show that the great ice-sheet continued 

 its progress until it reached the edge of the 100-fathom plateau, 40 

 or 50 miles beyond the Outer Hebrides, and then gave off its ice- 

 bergs in the deep waters of the Atlantic. 



5. " Notes on the Glacial Phenomena of the Hebrides." By J. 

 E. Campbell, Esq., F.G.S. 



This communication consisted of notes extracted from the author's 

 journal, giving his observations of indications of glacial action in 

 various islands of the group of the Hebrides. Heynish in Tiree is 

 500 feet high, and has many large perched blocks on its top. These 

 blocks are of gneiss ; and the author thought they came from the 

 north-west. The Barra islands are described as rocky, and resem- 

 bling the hill-tops of a submerged land. All ice-marks found by the 

 author seemed to him to come from the north and west. He thought 

 that the final grinding was given by floating ice when the land was 

 more submerged than at present. At Castle Bay, in Barra, the au- 

 thor observed well-preserved glacial striae at the sea-level in a direc- 

 tion from N.N.W. The whole island is glaciated and strewn with 

 perched blocks. Glacial indications were also observed in South Uist, 

 Benbecula, and Skye ; and the author stated that, on the whole, he 

 was inclined to think that the last glacial period was marine, and 

 that heavy ice came in from the ocean, the local conditions being- 

 like those of Labrador. The author regarded most of the lake- 

 basins of the Hebrides as formed by ice-action, and considered that 

 the ice by which those islands were glaciated came from Greenland. 



