ilie Old Bed Sandstone of Orkney. 335 



stones. This fault is well seen on the shore, a short distance 

 to the north-east of Spurness, where the red and yellow sand- 

 stones which dip to the west at an angle of 40° are brought 

 into conjunction with the grey flags. The effect of this dis- 

 location is also well exposed on the shore in Stranquoy Bay. 

 The chocolate-coloured sandstones and shales are seen on the 

 east side of the fault dipping in a south-westerly direction ; 

 while to the west of the fault the grey flags are bent round in 

 the form of an arch. The effect of this dislocation is shown 

 on the accompanying sheet of horizontal sections. 



To the east of Stranquoy the arenaceous series, which is 

 brought in by the fault just described, is traceable for nearly 

 a mile. The red and yellow sandstones are admirably seen 

 in Pool Bay and on the shore at Hack Ness, having a per- 

 sistent dip to the west at angles varying from 15° to 25°. A 

 thin zone of interbedded flagstones is exposed in the bay to 

 the west of Hack Ness, which reminds the observer of similar 

 zones on the same horizon in Eday. 



The gradual passage of this arenaceous series downwards 

 into the flagstones is presented on the shore at Moy Ness, 

 where the same alternations of flags and sandstones at the base 

 is observable, which obtains in Eday. Northwards along the 

 shore towards Bacaskeal Bay there is a steady descending 

 series of grey and purple flags. 



In the northern promontories of the island, and specially 

 along the shore from Hermaness Bay to the Holms of Eyre, 

 the grey and purple flags are repeated by gentle foldings. 

 There is, therefore, no great thickness of strata exposed in 

 the central portion of Sanday. The time at our disposal did 

 not permit us to visit the north-eastern promontories of 

 Sanday, nor the island of North Eonaldshay; but from the ob- 

 servations of previous observers only the Flagstone series 

 seems to be represented at these localities. 



The greater portion of the island of Stronsay is occupied 

 by the flagstones, but at one or two localities there are 

 small detached areas of the arenaceous series. On the north- 

 ern headlands, the gTey flags are exposed dipping in a north- 

 westerly direction, and the same inclination is observable in 

 Odin Bay and Linga Sound. About a mile to the north of 



