of the Island of Bute. 87 



the north-east of Ireland. These rocks attain a much more 

 complete development than in this country, both geographi- 

 cally and in relation to the number and variety of the beds. 

 Tliey extend continuously over an area of upwards of 1000 

 square miles; and while the thickness is, on an average, about 

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

 The whole series reposes on the chalk formation, while the 

 corresponding rocks of this country rest upon the old red and 

 carboniferous systems. Now in this series the lignites occupy 

 a determinate place ; they occur in the middle region, asso- 

 ciated with the steatites and variegated ochres, which are 

 always largely developed wherever the series approaches to 

 completeness. Instances may be seen at various points in the 

 cliff's 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 

 the 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. 



IV. Altered Dolomites. 



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 phaenomena are re- 

 markably well exhibited by them, and can be studied together 

 in a small space. Crystals of quartz and other substances are 

 developed in the shale beds near the contact. The dikes can 

 in some instances be traced continuously for several miles, 

 preserving the same direction, and the same width — two or 

 more are sometimes seen to meet and coalesce for some di- 

 stance 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 usual 

 alterations now universally acknowledged to be the result of 

 igneous action. 



A remarkable change is produced on the Kilchattan lime- 

 stone by one of these dikes. Its direction is very nearly the 

 same as the dip of the limestone, and the effects are well seen at 



