The Old Bed Sandstone of Orkriey. 339 



Mull Head and Air Point, Flagstones only, are exposed on 

 the shore to the east of St Mary's, and also along the road 

 from Grsemeshall to Kirkwall, save where the narrow patch 

 of red sandstones already mentioned crosses from Inganess to 

 Scapa, 



In Sonth Ronaldshay the lowest beds exposed are to be 

 met with at its southern extremity, where they form the 

 Old Head overlooking the Pentland Firth. Here the rocks 

 consist of grey calcareous flags, charged with abundant 

 remains of Coccosteus and other ordinary Caithness fishes, 

 which are well preserved as in Caithness, and are not 

 represented by a black lead-like smudge characteristic of 

 those from Skail. Following the eastern coast line, these 

 beds continue for a consideral)le distance Avith a northerly 

 dip. There are several faults, some of which are occupied 

 by veins of barytes and iron pyrites, but they seem not 

 to be of any great magnitude. A little to the north of 

 Halcro Head, the flags pass under a series of yellow and 

 red sandstones and red shales, which at Windwick are 

 suddenly truncated by a large east and west fault, the 

 effect of which is to bring up the underlying flagstones. 

 Near the fault flagstones are inclined towards it, but they 

 soon recover their northerly dip, and at Stow Head once more 

 dip below the sandstones. Owing to the sandstones being 

 arranged in a small trough, the flags soon reappear, and after 

 rolling about for some miles along the coast line, they 

 finally plunge under the sandstones near the mouth of 

 Watersound, never to reappear on South Eonaldshay; for the 

 red sandstones, with occasional thin intercalations of red flags 

 and massive bands of red marly clay, extend to Crow Point 

 in the extreme north-west. These beds are continued alono- 

 their strike into Burra, where the passage from the flags 

 into the red sandstones is well shown at the eastern entrance 

 to Watersound. The islands of Flota, Fara, and Cava, 

 show the same alternation of flagstones with red and yellow 

 sandstones and red marls. In Flota the dip is almost north 

 at Pan Hope, where the passage from the flagstones to the 

 sandstones is well seen ; while in Fara and Cava, the inclina- 

 tion is more to the north-east. 



