M u. Bryce on the Geology of tlie Island of BuU. 205 



among the numerous trap rocks examined in the course of the survey of 

 the western islands." Ho has not, indeed, described any such strata: 

 yet casual mention is made (vol. I., p. 376) of an iron clay and jaspery 

 tanco, forming ( w tensive beds in the trap of the cliffs of Talisker, in 

 Skye, — tho same in which the lignite also occurs — and that these 

 are often variegated with ™d, grey, and purple colours. No further 

 doscriptif.ii is given, nor is tho precise position of tho coal mentioned, 

 the cliffs being very difficult of access. But even by such a brief notice 

 tho steatitic beds and variegated ochres are easily recognised ; and though 

 these characters are not very distinctly marked in the beds we have been 

 describing in Bute, yet they apply exactly to tho red and variegated 

 ochres which occur as members of the trap series of the north-east of 

 Ireland. This class of rocks attains there a much more complete deve- 

 lopment than in this country, both geographically and in relation to tho 

 number and variety of the beds. They extend continuously over an area 

 of upwards of 1003 square miles; and while the thickness is, on an 

 average, about 300 feet, in very many cases it reaches to 1100 or 1200 

 feet. Tho whole series reposes upon the chalk formation, while the 

 corresponding rocks of this country rest upon the old red and carbonifer- 

 ous systems. Now in this series the lignites occupy a determinate place, 

 they occur in the middle region, associated with the steatites and varie- 

 gated ochres, which are always largely developed wherever the series 

 approaches to completeness. Instances may be seen at various points in the 

 cliffs at the Giant's Causeway, at Ballintoy, at Glenarm, and at numerous 

 places in the interior of the district. Similar beds are associated with 

 the lignites of Bute and Skye, and most probably also of others of the 

 Western isles, though the notices are too vague to be relied on. We are 

 thus led to tho interesting conclusion, that such association is not acci- 

 dental, but has been determined by the prevalence, over a considerable 

 area, of certain similar and fixed conditions, regulating the succession of 

 the igneous eruptions, the mode of their consolidation, and the periods of 

 repose during which the productions of the adjoining dry land were swept 

 down and entombed. 



8. The dikes of Bute are composed of greenstone or basalt, and are 

 extremely numerous. They traverse the different strata in every possible 

 direction, and are well seen upon the rocky parts of the coast. All 

 the usual phenomena are remarkably well exhibited by them, and can 

 be studied together in a small space. The dikes can in some instances 

 In- traced continuously for several miles, preserving the same direction, 

 and the same width, — two or more are sometimes seen to meet and to 

 coalesce for some distance, and again to separate, — a narrow dike branches 

 off into several filaments, which unite again, — portions of the rock which 

 is traversed are frequently found entangled in the dike; and these, as 

 well as the contiguous strata, present the u>nal alterations now universally 

 acknowledged to be the result of igneous action. It is unnecessary to 

 enter into any detail respecting these changes ; but there are two 



