398 MR JOHN S. FLETT ON 



hills are the highest in the North Isles of Orkney, rising to heights of over 800 feet ; and 

 if we allow 1000 feet for the total thickness of rock exposed, we have an estimate which 

 cannot be far from the truth. Few fossils are yet known from it : Dipterus 

 vcdencienesii (Sedgw. and Murch.), Homosteus Milleri (Traq.), Glyptolepis paucidens 

 (Ag.), with the characteristic fossils Thursius pholidotus (Traq.) and Coccosteus minor 

 (Miller). These latter occur in what are about the lowest beds of the island, a belt of 

 thin blue calcareous flags seen best at Sacquoy Head on the north-west corner, and 

 striking southwards through the island, to outcrop again at the Taing of Tratland and 

 the adjoining shore. At Sacquoy Head they overlie a bed of conglomeratic sandstone, 

 with pebbles up to the size of a walnut, of gneiss and quartzite mostly, and resembling 

 thus the rocks of Heclabir, to be subsequently described. In Egilshay the easterly dip 

 continues, but here much steeper, with evident crushing and fracture of the rocks ; * and I 

 think it likely that through this island passes a line of dislocation, evidence of which 

 is to be found in the Gait of Shapinshay to the south, and in the district of Rackwick in 

 Westray to the north, in both of which places the appearances point to a similar 

 disturbance. This would, in fact, be a north and south fault, skirting the Eday syncline, 

 like that already described in the West Mainland anticline, and those also described in 

 several places by Peach and Horne (Sanday, Berstane, Holm). 



If the section be now continued across the Westray Firth to Eday, we find, as 

 described by Peach and HoRNE,t a strip of flagstones, with a very steep easterly dip, 

 ranging from Ferstness to Sealskerry, and bounding on the west the area of the Eday 

 sandstones. These lie in the trough already described by these authors ; and, as they 

 showed, the only other flagstone area in the island is one which stretches from Warnoss 

 to the Graand on the south shore, and thence N.N.E. to the Kirk of Skaill and the 

 inner corner of Backaland Bay on the east side. As the centre of the syncline runs 

 from Zoar in Sealskerry to Calf Sound in the north, these flagstones have a W.N.W. dip 

 of about 15°, and they have been brought up by a small fault against the red sandstones 

 which occupy the south-east corner of the island. 



In Sanday the yellow and red sandstones occupy the south-east end, as shown by 

 Prof. Heddle,J broken by a fault which, running north and south through Spurness Pro- 

 montory, brings up again for a brief space the underlying dark grey flags.§ Beyond 

 them, to the north and east, the whole island consists of flags which form a well-marked 

 anticline, their westerly members dipping to the west like the Eday beds, under which 

 they pass, but arching over on the south shore of Otterswick Bay and near Geramont 

 House, so that at Taftsness, Newark, and the Start the prevalent dips are to the east. 

 These Sanday flags yielded little of value to my search, Glyptolepis paucidens (Ag.), 

 Dipterus vcdencienesii (Sedgw. and Murch.), with a few well preserved fragments of an 

 Osteolepid fish being all I noticed. There can be no doubt that they are a repetition of 



* Noted by Jameson, Scottish Isles, ii. 239. 



t Peach and Horne, Old Red Sandstone of Orkney, pp. 8 and 9. 



| Heddle, Geognosy of Scotland, part v. p. 101. 



§ Peach and Horne, Old Red Sandstone of Orkney, p. 7. 



