Vol. 52.] BASALT-PLATEAUX OF NORTfi-WESTERN EUROPE. 389 



allowed to recognize it among some of the basalt-sheets included 

 among the gabbros. 



Like their counterparts in the Inner Hebrides, these rocks have 

 not only been traversed by basic dykes, but have been invaded by a 

 large mass of granophyre. The junction of the acid and basic 

 materials repeats the evidence already cited from Mull, Hum, and 

 Skye, aud proves beyond all question that the acid rock is the 

 younger of the two. The characters of this junction will be given 

 in the next section of this paper. 



It is interesting to observe that, while in St. Kilda no relic of any 

 basaltic plateau has been preserved, in the Faroe Islands, on the 

 other hand, no sign has been revealed by denudation that the 

 volcanic plateau of that region has any eruptive core of gabbro or 

 of granophyre. During my cruises round these islands and through 

 their channels, I was ever on the outlook for any difference in 

 topography that might indicate the presence of some eruptive boss 

 like the gabbro- and granophyre-masses of the Inner Hebrides. 

 But nothing of that nature could be discerned. Everywhere the 

 long level lines of the bedded basalts mounted up to the crests of 

 the ridges and the tops of the highest peaks. Though I cannot 

 assert that no intrusions of gabbro or of granophyre exist among 

 the Faroe Islands, I feel confident that any such masses which 

 may occur must be of quite insignificant dimensions, and do not 

 make the important feature in geology and topography which they 

 do among the Inner Hebrides. 



VII. The Granophyre Intrusions. 



Having recently brought the subject of the Tertiary granophyres 

 before the Society, 1 I shall content myself in the present paper 

 with an account of some additional examples of their occurrence 

 and of their relations to the other members of the volcanic series. 



St. Kilda supplies fresh evidence of much interest in this part 

 of the volcanic history. The visitor, in approaching the island, 

 especially from the southern or northern side, will notice the same 

 two strongly contrasted topographical features as those that are so 

 well exhibited in the centre of Skye. Along the western side rise 

 the black rugged crags of gabbro. The eastern precipices are pale in 

 colour, and are capped by rounded or conical hills, which towards 

 the interior send down long screes of grey or russet-coloured 

 debris. Their forms are so like those of the Red Hills of Skye 

 that the geologist recognizes their true nature and respective limits, 

 even before setting foot on them. 



To Macculloch we are indebted for the first good description of 

 the rocks of St. Kilda. 2 He clearly identified the pale rock of the 

 eastern half of the island with the ' syenite ' or granophyre of Skye, 

 and he further remarked that it presented much resemblance to 

 some parts of the granite of Arran. He observed ' fragments of 

 trap penetrated by veins of syenite,' but he did not see these 



1 Quart. Joum. Geol. Soc. vol. 1. (1894) pp. 212-229. 



2 ' Description of the Western Islands,' vol. ii. (1819) p. 54. 



2d2 



