

METAMORPHISM IN IRELAND. 391 



the north of Perth, to show that those parts of the Upper Limestone 

 beds which are associated with serpentine are richest in mineral;?, 

 where both beds are included in gneiss ; while the comparatively 

 implicated Lower Limestone in mica-schist is poor in minerals. 1 

 Limestones contain garnets as they approach granite. 



The Isle of Man. The granite of the central axis of the Isle of 

 Man, seen at Barrule and North of Laxey, is succeeded by very little 

 gneiss and mica slate, much Cambrian schists, from which the mica- 

 schist and gneiss are metamorphosed, and quartz rock. The mica- 

 slate is traversed by veins of quartz and schorl. 2 



North of Ireland. The older strata of the North of Ireland may 

 be considered as in part a prolongation of those of Scotland ; thus the 

 extensive spread of mica-slate in Londonderry and Donegal is a pro- 

 longation of the line of the chain of the Grampians, continued through 

 Jura and Islay ; and the clay slate ridges which border the Mourne 

 mountains run in the direction of the Mull of Galloway and the clay 

 slate chain of the South of Scotland, while between these two systems 

 of slates, occupying a basin-shaped depression, are red sandstone, car- 

 boniferous limestone, and other strata of newer origin, corresponding 

 to those which separate the analogous chains in Scotland. 



The mica slate rocks are principally of the chloritic varieties with- 

 out garnets, but contain hornblende. Laminated crystalline limestone of 

 different colours, containing talc, quartz, hornblende, or pyrites, with 

 veins of quartz, chlorite, and calcareous spar, occur in the mica slate 

 in many parts of Antrim and Londonderry. Hornblende slate like- 

 wise forms distinct bands in the mica slate of this region, and felspar 

 porphyry is interposed. 3 



South of Ireland. In the south-eastern part of Ireland mica slate 

 forms two ranges along the eastern and western boundaries of the 

 granite, and wherever it occurs is in direct contact with the granite. 

 On the eastern side of the granite it runs in a narrow course north- 

 east and south-west, dipping deeply south-east, and consists of alter- 

 nate layers of mica and quartz of extremely variable thickness. On 

 the eastern brow of Rochetown Hill mica slate runs into a natural 

 hollow of the granite, still retaining the north-east and south-west 

 direction of its strata. On Maulin Hill it is singularly and fantasti- 

 cally contorted on a small scale. There is a prolongation of the 

 body of mica slate at the head of Glenmacanass, gradually narrowed 

 in its western progress, and constituting a wedge-like mass inserted 

 into the body of the granite, and enclosing apparently a bed of granite 

 six to ten yards in width, besides irregular masses of granite incorpo- 

 rated with the slate. In the district, greenish, sectile, chloritic slate lies 

 embebbed in the mica slate, and is used for various purposes of 

 architecture and ornamental carving. 



In Glenmalur occurs a remarkable instance of decided alternation 

 of granite and mica slate. In a space of 208 fathoms no less than 



1 Heddle, Trans. Roy. Soc. Scot, vol. xxviii. p. 311. 



2 Henslow, in Geol. Trans. ; Cmnming's " Isle of Man." 



3 Berger in Geol. Trans, and Mem. Geol. Surv. Ireland. 



