414 MR JOHN S. FLETT ON 



plete that the fault which crosses the isthmus at Dingieshowie cuts out the passage beds 

 underlying the yellow sandstones. These are seen in the shores farther west, at Stem- 

 buster, where they consist of thin courses of yellow sandstone with slaty flags between, 

 forming a very gradual transition between the two types of sediment. Above these 

 ' passage beds ' lies a series of red marls, with thin yellow and brown sandstones (40 feet) 

 between, recalling in some ways the beds described as occupying a similar position in 

 Eday. The exact point at which the base of this series should be drawn is a matter of 

 some doubt, as among the lowest of them occur beds crowded with Dipterus valen- 

 cienesii (Sedgw. and Murch.), and containing also Asterolepis, sp. nov.,but containing no 

 other fishes, an observation due to Mr Magnus Spence. Traced upwards, the red beds 

 pass gradually into a pure massive yellow sandstone, which forms the high cliff below 

 Tornpike, and is, no doubt, the same as that of Delday's Banks. These lowest beds are 

 exposed also in other parts of the parish, as at Braebuster and the shores to the south of 

 it, where thin grey flags pass gradually up into yellow sandstones. In the north shore 

 of Deerness a very similar series occurs at Halle, and extend thence to near the Cove- 

 nanters Monument, lying very flat, and forming the extreme N. edge of the syncline ; 

 and these rocks must again outcrop in Sandside Bay, between the flags which form its 

 northern side and the yellow sandstones to the south, though here the rock is concealed 

 by the blown sand which occupies the centre of the bay. Just north of the Brough of 

 Deerness the presence of a few red beds beneath the yellow sandstones is well seen in a 

 lofty cliff, and again the same feature is to be observed in the shore below Horraquoy. 

 The yellow sandstones recall, in very many respects, those of Shapinshay. They are of 

 much the same thickness, 400 to 500 feet, and through them lie here and there belts of 

 thin grey calcareous flags, which are the chief source of the John o' Groats fossils of 

 Orkney. They contain Dipterus macropterus (Traq.), Tristichopterus alatus (Egert.), 

 and Microbrachius Dichi (Traq.), the first especially in great abundance, and often in 

 fine preservation ; and it is probable that through the low lying centre of the parish these 

 largely replace the yellow sandstone series. 



A further point of similarity to the yellow sandstones of Shapinshay is furnished by 

 the presence in these beds of a zone of contemporaneous volcanic rocks of basic com- 

 position. These occur rather above the middle of the yellow series, and, as in the 

 district previously described, they are immediately associated with a belt of grey flags 

 intercalated among the sandstones. They consist of both ashes and lavas, and in 

 addition there are several intrusive sheets which, from their composition and general 

 character, are undoubtedly to be ascribed to the same volcanic source. 



At the extreme south-east corner of the parish, at the Point of Ayre, a series of 

 volcanic rocks form a narrow belt running W.N.W. in the land, and outcropping on the 

 seashore. The general dip in this quarter is S. and S.S.E., and from Horraquoy 

 southward along the east shore we pass over a gradually ascending section of the lower 

 members of the yellow sandstones. This dip continues to the Point of Ayre, which 

 consists of beds of flagstone, and these, though somewhat faulted, evidently are to be 



