164 



HARDWICKE'S SCIENCE -GOSSIP. 



GEOLOGY, 



The Glacial Phenomena of the Long 

 Island, or Outer Hebrides. — A paper on this 

 subject has recently been read before the Geological 

 Society by James Geikie, LL.D. The author gave a 

 detailed account of the glacial phenomena of Harris 

 •and the other islands that form the southern portion 

 of the Outer Hebrides. Evidence was adduced to 

 show that Lewis has been glaciated from S.E. to 

 N.W., and the shelly boulder-clays and interglacial 

 shell-beds of that part of the Long Island were de- 

 scribed in detail. Harris, North Uist, Benbecula, 

 South Uist, Barra, and the other islands that go to 

 form the chain of the Long Island were successively 

 described under the headings of Physical Features, 

 Geological Structure, Glaciation, Till or Boulder-clay, 

 Erratics and perched blocks, Morainic debris and 

 Moraines, Freshwater Lakes and Sea-lochs. Numerous 

 bearings of stride, which abound, were given, and 

 these were held to prove that the whole Outer 

 Hebrides have been glaciated by ice that flowed out- 

 wards from the mainland of Scotland. The position 

 of abundant ?-oc/ies moutonnees points to the same con- 

 clusion, and this is still further supported by the 

 "travel" of the Till. That deposit is generally 

 absent or very sparingly present on the rock-faces 

 that look towards the mainland, but it is heaped up 

 in their rear, and spreads over the lower tracts that 

 slope gently towards the Atlantic. On the west side 

 of the islands not a few boulders occur in the Till, 

 which have been derived from the east ; and the same 

 is true of certain erratics lying loose at the surface of 

 the ground. The islands are well glaciated up to a 

 height of 1,600 feet above the sea ; and the line of 

 demarcation between the glaciated and non-glaciated 

 areas is extremely pronounced. Above 1,600 feet the 

 hills show rugged, splintered, jagged, and sometimes 

 serrated tops. The author regarded the Till or 

 boulder-clay as the morainic material that gathered 

 underneath the ice, and proof of this is given. Erratics 

 and perched blocks are very numerous, and most of 

 these, as well as much of the morainic debris, are 

 believed to have been dropped where we now find 

 them during the final melting of the ice-sheet. It was 

 shown, however, that certain erratics and perched 

 blocks and some well-marked moraines are due to 

 local glaciers, as are also some of the striations in a 

 few of the mountain valleys. The origin of the rock- 

 basins, which are now lakes, was discussed, and 

 attributed to the erosive action of ice. To the same 

 cause were assigned the rock-basins which occur in 

 certain of the sea-lochs. In concluding, the author 

 pointed out that we may now arrive at a true estimate 

 of the thickness attained by the ice-sheet in the north- 

 west of Scotland. If a line be drawn from the upper 

 limits of the glaciations in Ross-shire (3,000 feet) to a 

 height of i,6co feet in the Long Island, we have an 

 incline of only 1 in 210 for the upper surface of the 



ice-sheet ; and of course we are able to say what 

 thickness the ice reached in the Minch. Between 

 the mainland and the Outer Hebrides it was as much 

 as 3,800 feet. No boulders derived from Skye or the 

 mainland occur in the Till of the Outer Hebrides, 

 and this was explained by the deflection of the lower 

 portion of the ice-sheet against the steep wall of rock 

 that faces the Minch. The underpart of the ice that 

 flowed across the Minch would be deflected to right 

 and left against the inner margin of the Long Island ; 

 and the deep rock-basins that exist all along that 

 margin are believed to have been scooped out by the 

 grinding action of the deflected ice. Towards the 

 north of Lewis, where the land shelves off gently into 

 the sea, the under strata of the ice-sheet were enabled 

 to creep up and over the district of Ness, and thus 

 gave rise to the lower shelly boulder-clay of that 

 neighbourhood, which contains boulders derived from 

 the mainland. The presence of the overlying inter- 

 glacial shell-beds proves a subsequent melting of the 

 ice-sheet, and a depression of the land for at least 

 200 feet. The overlying shelly boulder-clay shows 

 that the ice-sheet returned and overflowed Lewis, 

 scooping out the older drift-beds and commingling 

 them with its bottom moraine. The absence of 

 kames was commented upon, and shown to be in- 

 explicable on the assumption that such deposits are 

 of marine origin ; whilst if they be of torrential origin 

 their absence is only what might be expected from 

 the physical features of the islands. The only traces 

 of post-glacial submergence are met with at merely a 

 few feet above present high-water mark. 



The Fossil Fungus. — Too much credit cannot 

 be given to Mr. Butterworth for his labours on fossil 

 plants, carried on for so many years under great diffi- 

 culties but with great perseverance, and with most 

 important results. Prof. Williamson has again and 

 again expressed his obligations to Mr. Butterworth ; 

 and the collections of the British Museum have several 

 valuable specimens prepared by Mr. Butterworth's 

 own hands, the importance of which I have testified 

 to on several occasions. No doubt Mr. Butterworth 

 observed the fossil fungus in his specimens before 

 they were sent to London, although Mr. Smith and 

 myself were ignorant of it. But the fungus had al- 

 ready been observed by myself, and shortly described 

 from specimens in the British Museum prepared by 

 Mr. Norman, and the interest of Mr. Butterworth's 

 specimens to me, when they were shown me by 

 Mr. Young, was that they confirmed the specimens 

 I already possessed, and added to my knowledge of 

 the fungus. The two Pahrozoic fungi which Mr. 

 Butterworth refers to could not include the Neozoic 

 parasite in the fern-stem from Heme Bay, as he sup- 

 poses. These two Palaeozoic fungi were — 1. The 

 curious mycelium masses found at Newcastle by Mr. 

 Atthey, and described and figured in his "Annals 

 and Magazine of Natural History"; and 2. The 



