418 MR JOHN S. FLETT ON 



shore of Watersound, just cast of St Margaret's Hope. At Stews Head they contain a 

 few reddish bands. In South Ronaldshay the yellow series is largely developed, and, 

 with the exception of the district from Widcwall to St Margaret's Hope, and thence to 

 Hoxa, they occupy all the areas marked on the map as belonging to John o' Groats 

 beds. A fine section of massive yellow sandstones, with a few flag-beds, is seen extending 

 from Barswick on the west side, north to Herston Head. It is broken by several faults, 

 but there can be no doubt that in thickness it is greater than any other section of 

 the same rocks elsewhere exposed in Orkney. Among these beds no trace of a volcanic 

 zone has yet been discovered, and as yet no John o' Groats fossils have been obtained 

 from any of the South Isles. Their relationships are such, however, as to leave no 

 doubt whatever of their position in the series. 



In the district around Melsetter in the island of Hoy, according to Peach and Horne, 

 bands of yellow sandstone occur, overlying conformably the flags which form the south 

 end of the island. These resemble greatly the upper Old Red Sandstones of the west 

 end of Hoy, which unconformably overlie the flags. Now, at the west side of Hoy, 

 opposite Graemsay, the upper sandstones rest on flags which are to be correlated with 

 the Orcadian beds of the opposite shores of Stromness. This is clear proof of the great 

 erosion which must have preceded the deposition of the upper Old Red series in Orkney, 

 as time sufficient for the removal of all the Rousay rocks and all the John o' Groats 

 rocks of Orkney must have elapsed before the upper beds were laid down on the up- 

 turned edges of the Stromness flags which form the base of the Old Man of Hoy. 



The Red Sandstones of the John o' Groats Beds. 



The red sandstones of the John o' Groats beds of Orkney have their greatest 

 development in South Ronaldshay, in the extreme south, and in Eday, at the extreme 

 north of the country, while in the intervening districts their thickness is small. In 

 Eday, they form the entire north end of the island, and thence pass down the centre to 

 Sealskerry Bay. Some of the highest elevations along this line have a height of 350 

 feet, and the least possible estimate of the thickness of the whole series cannot be less 

 than 600 feet. The yellow sandstones of this island are, however, of only slight thick- 

 ness, and it is possible that the red beds, in fact, replace the yellow, which further south 

 have a much greater development. Red sandstones form also the south-east corner of 

 the island around the point of Veness. To the geologist these beds are somewhat 

 uninteresting. No fossils have been found in them, and they contain no con- 

 temporaneous volcanic rocks. The absence of fossils is perhaps due to the fact that 

 there are no beds of close-grained flag suitable for the preservation of organic remains. 

 The beds themselves consist of coarse red sandstones, often in thick beds, alternating 

 with red shales and marls, with sometimes a greenish or greyish shale. In Eday the 

 sandstones greatly preponderate, and in some places are so coarse as to deserve the title 

 of 'grits.' No traces of any chemical deposit, such as rock salt or gypsum, occur any- 



