I. Introduction.

In a former paper which we communicated to the Society on "The Glaciation of the Shetland Isles," we endeavoured to show how the evidence supplied by the striated surfaces, the roches moutonnées, and the dispersal of the stones in the Boulder-clay points to the conclusion that Shetland had been glaciated by Scandinavian ice. It was further argued that during the climax of glacial cold the Scandinavian and Scotch ice-sheets coalesced on the floor of the North Sea, and that the great outlet for the combined ice-sheets was towards the north-west by the Pentland Firth and the Orkney Islands.

In the course of the autumn of 1879 we visited nearly all the Orkney Islands for the purpose of continuing our researches with reference to the extension of the ice in the North Sea in the Glacial period. In the paper now presented to the Society we purpose to give a summary of the results of our observations. At the outset we may state that they furnish a remarkable confirmation of the conclusions already arrived at regarding the westerly and northwesterly movement of the ice. Moreover, the presence of stones in the Boulder-clay, which must have been derived from the mainland of Scotland, and the discovery of abundant remains of marine shells in the same deposit, though in a fragmentary state, are of the utmost importance in guiding us to a satisfactory solution of the question.

No description of the glacial phenomena of Orkney has hitherto been published^*. Some references were made by Professor Geikie to

^* Since this paper was written, our friend Mr. Amund Helland has sent us a copy of his paper "Ueber die Vergletscherung der Färoër Inseln," which appeared in the 'Zeitschrift der deutschen geologischen Gesellschaft,' 1879. We are glad to see that Mr. Helland has arrived at the same conclusions as ourselves regarding the north-westerly movement of the ice in Orkney, from independent observations made in the course of last year.

page 649 the existence of roches moulonnées with striated surfaces, Boulder clay, and valley moraines in the islands in an article which appeared in 'Nature'^*. This article was written in reply to a letter by Samuel Laing, Esq., M.P., in which he asserted that there is no evidence that Orkney had participated in the general glaciation of Britain^†. So far from there being any lack of evidence regarding the glaciation of these islands, we hope to show that they contain abundant proofs of having undergone severe glacial conditions. Our observations, however, completely confirm Sir. Laing's statement that there are no raised beaches in the islands indicating changes of the relative levels of sea and land since glacial times.