372 



B. N. PEACH AND J. HORNE ON THE 



description of the geology of Papa Stour, Dr Archibald Geikie has referred 

 to two sections, one on the north side of Hamna Voe and the other on the 

 cliffs at the headland of Bordie, where the bedded lavas and grey flaggy sand- 

 stones are traversed by this sheet of pink felsite. In the course of our subse- 

 quent visit, we observed that, in Culla Voe, the sheet steals across the edges 

 of the lavas, while a thin lenticular offshoot from the main mass is forced in 

 like a wedge at a lower level between the diabase-porphyrites. Further, on the 

 south-eastern headlands, about a mile east of Hamna Voe, the pink felsite cuts 



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Fig. 9. — Pink spherulitic felsite showing marked columnar structure, north-west side of Papa Stour with outlying 



stacks — Foula in the distance. 



across the sandstones, and passes from a lower to a higher horizon, as shown in 

 the accompanying section. These and other sections which might be adduced, 

 plainly indicate the intrusive character of the Papa Stour sheet, since it not 

 only occurs on various horizons, but frequently eats its way upwards, when 

 traced along the base of the cliffs. There can be no doubt that the sandstones 

 and conglomerates with the associated lavas form the platform over which the 



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Fig. 10. — Pink felsite injected among red sandstone, on sliore one mile east of Hamna Voe, Papa Stour. 1, Red 

 and purple amygdaloidal diabase-porphyrites ; 2, red sandstone and flags ; 3, pink spherulitic felsite. 



felsite spreads. It is equally clear, however, from the evidence obtained at 

 the Horn of Papa, that the sheet must have been covered by sedimentary de- 

 posits. There, on the cliff top, the pink felsite is overlaid by a patch of red 

 felspathic sandstones which are nearly horizontal. The sandstones in immediate 

 contact with the felsite have been hardened and altered to some extent by the 

 intrusion of the igneous mass, and in some places portions of the sandstone and 

 felsite may be seen adhering together, clearly showing the effects of contact 

 metamorphism. The occurrence, therefore, of this isolated patch of sandstone is 

 invested with special interest, inasmuch as it helps us to realise the denudation 



