324 Reports and Proceedings — 



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 Eoss-shire (3000 feet) to a height of 1600 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 3800 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 able 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 interglacial 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 inex- 

 plicable 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 miet with at merely a 

 few feet above present high- water mark. 



2. " Cataclysmic Theories of Geological Climate." By James 

 CroU, Esq., LL.D., F.E.S. Communicated by Prof. Eamsay, LL.D., 

 r.E.S., F.G.S. 



The author commenced by calling attention to the great diversity 

 of the hypotheses which have been brought forward for the explana- 

 tion of those changes in the climate of the same regions of the 

 earth's surface which are revealed by geological investigations, such 

 as alterations of the relative distribution of sea and land, of the 

 ecliptic, and of the position of the earth's axis of rotation, all of 

 which, he maintained, have proved insufficient or untenable. Sir 

 "William Thomson has lately maintained that an increase in the 

 amount of heat conveyed by ocean-currents, combined with the effects 



