Vol. 52.] BaSALT-PLATEATJX OF NORTH-WESTERN EUROPE. 



381 



sills, however, have been noticed by 

 previous observers, 1 and I have seen 

 others on the sides of Stromo, Kalso, 

 Kuno, and other islands. 



The most remarkable sill in the 

 Faroe Islands is probably that which 

 forms so prominent an object on the 

 western cliffs of Stromo, at the en- 

 trance into the Yaagofjord (figs. 24, 

 25). It is prismatic in structure, 

 and where it runs along the face 

 of the cliffs, parallel to the bedded 

 basalts among which it has been in- 

 truded, presents the familiar charac- 

 ters of such sheets. It runs along 

 the face of the precipice which rises 

 above the row of volcanic vents 

 already described. But it there 

 begins to ascend the cliffs obliquely 

 across the basalts, until it reaches the 

 crest of the great wall of volcanic 

 rock at a height of probably about 

 1000 feet above the waves. From 

 the crest of the precipice the up- 

 ward course of this sill is continued 

 into the interior of the island. It 

 pursues its way as a line of bold 

 crag along the ridges of the plateau, 

 gradually ascending till it forms the 

 summit of one of the most prominent 

 hills in the district. 



Some further idea of the enormous 

 energy with which tho sills were in- 

 jected may be formed from this 

 example, where the eruptive mate- 

 rials followed neither the line of 

 bedding nor a vertical fissure, but 

 took an oblique course through the 

 plateau-basalts for a vertical distance 

 of probably more than ] 500 feet. 



In Skye a series of remarkable 

 compound sills occurs where a central 

 sheet of acid rock is overlain and 

 underlain by a layer of basic mate- 

 rial. I have already described some 

 examples of this structure, and will 

 cite some others in a later part of 

 this paper. 



1 See in particular the description by 

 Trevelyan and Allan, and references by Prof. 

 James Geikie and Mr. Lomas already cited. 



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