648 » B. N. PEACH AND J. HOEKE ON THE 



46. The Glaciation of the Oekney Islands. By B. N. Peach, Esq., 



F.G.S., of the Geological Survey of Scotland, and John Horne, 



Esq.,' F.G.S., of the Geological Survey of Scotland. (Eead 



June 23, 1880.) 



[Plates XXVI. & XXVII.] 



Contents. 

 I. Introduction. 

 II. Geological Structure. 



III. Glaciation. , 



IV. Boulder-clay, 

 V. Moraines. 



VI. Erratics. 

 VII. Conclusion. 



(a) Orkney glaciated by Scotch ice. 



{b) Explanation of the occurrence of marine shells in the 



Boulder-clay, 

 (c) Absence of gravelsi and raised beaches in Orkney. 



I. Inteodtjction. 

 In a former paper which we communicated to the Society on " The 

 Glaciation of the Shetland Isles," we endeavoured to show how: 1. 

 evidence supplied by the striated surfaces, the roches moutonnees, and 

 the dispersal of the stones in the Boulder-clay points to the con- 

 clusion that Shetland had been glaciated by Scandinavian ice. It 

 was further argued that during the climax of glacial cold the Scan- 

 dinavian 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 Eirth 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 north- 

 westerly 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 Faroer Inseln," which ap- 

 peared in the ' Zeitschrift der deutschen geologischen Gesellschaft,' 1879. We 

 are glad to see that Mr. Helland has arrived at the same conclusions as our- 

 selves regarding the north-westerly movement of the ice in Orkney, from inde- 

 pendent observations made in the course of last year. 



