Vol. 52.] BASALT-PLATEAUX OF NORTH-WESTERN EUROPE. 



341 



character, and by their weathering into globular forms which at a 

 little distance give them a resemblance to agglomerates. 



AVe have here an intercalated group of strata upwards of 40 feet 

 thick, consisting partly of tuffs and partly of fine clays, which may 

 either have been derived from volcanic explosions or from the 

 atmospheric disintegration of basaltic lavas. Through some of 

 these strata abundant carbonaceous streaks and other traces of 

 plants are distributed, while among them lies a band almost wholly 

 composed of compressed vegetation. Unfortunately none of the 

 strata at this locality seem to have preserved the plant-remains with 

 sufficient definiteness for identification. There can be no doubt, how- 

 ever, that they were terrestrial forms like those of Mull and Antrim. 



This coal, with accompanying sedimentary deposits, has been 

 traced through Sudero, and another outcrop, possibly of the same 

 horizon, occurs on Myggenaes, the extreme western member of the 

 Faroe group, at a distance of some 40 miles. 1 



Though good coal is not well developed in the Tertiary volcanic 

 plateaux of the British Isles, I have found coaly layers to be ex- 

 tremely abundant there. And as the vegetable matter may confidently 

 be assumed always to indicate terrestrial vegetation, the presence 

 of these carbonaceous bands may be regarded as good evidence of 

 some lapse of time between the eruption of the basalts which they 

 separate. I have observed that they not infrequently form the 

 highest member of a group of intercalated sediments between two 

 sheets of basalt. This relation is strikingly exhibited in the isle of 

 Canna in connexion with the river-gravels, to which more detailed 

 reference will be made in a later part of this paper. But I may 

 here cite an interesting example which occurs at the base of the 

 lofty sea-cliff of An Ceannaich, to the south of Dunvegan Head, on 

 the western coast of Skye (fig. 7). 



Fig. 7. — Intercalated group of 

 strata between basalts. An 

 Ceannaich, western coast of 

 Skye. 



At the base of the precipice 

 ledges of a highly amygdaloidal 

 basalt (a) show a singularly 

 scoriaceous and amygdaloidal 

 structure, with abundant and 

 beautiful zeolites, the hollows 

 of the upper surface of the 

 sheet being filled in with dark 

 brown carbonaceous shale, form- 

 ing a layer from 1 to 14 inches 

 thick, marked by coaly streaks 

 and lenticles (0). A band of 

 green and yellow sandstone (c) 

 next supervenes, which, from its 

 pale colour, attracts attention 

 from a distance, and led me, 

 while yachting along the coast, 

 to land at the locality, in the 

 hope that it might prove to be a plant-bearing limestone. This 



See in particular J. Geikie, TranB. Roy. Soc. Edin. vol. xxx. (1880) p. 229. 



2a 2 



