THE OLD RED SANDSTONE OF THE ORKNEYS. 411 



laid by a few feet of red beds, and these by 20 feet of coarse flags (in which I found no 

 fossils). Over these flags, which no doubt are the same as those of London Bay, come 

 a few yellow beds, which rapidly give place to the red sandstones of Sealskerry Bay. 



In the south end of Sanday these beds recur, and form the western edge of the 

 promontory of Spurness, disturbed and set on end by a north and south fault, which 

 brings up with them the underlying beds of flagstones in a narrow strip. A thick 

 conglomerate occurs among them at Heclabir, but in other respects they differ little 

 from the Eday sandstones, though, from their limited distribution, no very complete 

 idea of their features can be formed. After we cross the fault above mentioned, we find 

 the red sandstones in great strength, forming the shore to near the Noust of Boloquoy 

 on the north coast. Here yellow and red beds, mixed, strike along the shore, and, 

 slightly faulted at Grunnavi Head, continue with a dip W.N.W. to Blue Geo, where the 

 flao-s again come id. The thickness here is not great; but owing to the presence of 

 several small faults, an exact estimate is not possible. These beds, traced along the 

 strike, emerge at Quoyness on the south shore, where, however, they are covered 

 by the blown sand of the beach. The yellow sandstones of Sanday show the same 

 features as those of Eday, and, like them, are of comparatively small thickness. 



The conglomerates which occur in these rocks of Eday and Sanday have already been 

 the subject of discussion by several writers.* Professor Heddle noted that at Heclabir, 

 in Sanday, occurred a bed of conglomerate about 14 feet in thickness, and that the 

 pebbles it contained consisted of "granites, more than one variety, gneisses, often chloritic, 

 porphyrys, and seemingly of quartzite, — rocks which are entirely different from the 

 primitive rocks near Stromness, and therefore rocks not occurring in the islands." t He 

 states also that both the pebbles and the cementing paste have a highly vitrified aspect, 

 and that he had a strong impression this was a volcanic conglomerate. Messrs Peach and 

 Horne state with regard to the beds of Eday, which form very insignificant belts at the 

 base of the red series — nowhere over a few inches in thickness — that " the included pebbles 

 consist of fragments of mica schist, quartzite, gneiss, granite, and other metamorphic 

 rocks, all stained of a reddish colour." J According to my own observations, all those 

 mentioned occur with one exception ; the commonest by far at Heclabir being a creamy 

 or white lustrous quartzite, in much rounded and waterworn pebbles, up to 6 inches in 

 diameter. At the latter locality I was unable to find any volcanic rocks, but there 

 were very numerous pebbles of grey limestone, which microscopic sections showed to 

 be entirely holo-crystalline and true marbles, without any trace of organic structure. 

 With these were others which at first puzzled me ; but on referring to Mr Peach, he at 

 once recognised them as cherts and cherty limestones from the Eillean Dhu series 

 of Durness (Cambrian) ; and the microscope showed that, like these, they were of oolitic 

 structure, though, so far as my examination went, by no means so perfect as in the 



* Jameson, Mineralogy of the Scottish Isles, vol. ii. p. 257. 

 t Heddle, Geognosy of Scotland, v. p. 103. 

 \ Peach and Horne, op. cit., p. 5. 



