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term to the first-mentioned rock, which occurs stratified in great 

 thick bands or beds, constituting the oldest stratified rock known in 

 Ireland. 



Mica Slate. 



The district in which Mica Slate is found lies in the north-east part 

 of the county. It extends from Gortnagross, three miles south-west of 

 Cushendall on the south, to Murlogh Bay, five miles east of Bally- 

 castle on the north, being about ten miles ; and from Cape Castle, near 

 Armagh, on the west, to Tor Head, on the east, about eleven miles. 

 Of this a portion is covered with chalk, and a part with trap and other 

 rocks, so that there is not perhaps above eighty square miles of Mica 

 Slate uncovered. 



Mica Slate is of different ages. 1. In Ireland the Mica Slate of 

 Donegal and the north of Mayo appears to be the oldest we know. 

 2. That on both sides of the great granite protrusion, which breaks up 

 through the Silurian rocks, and reaches from Dublin, through "Wicklow 

 and Wexford, to Brandon Hill, in Kilkenny, is of a later date. It is a 

 metamorphic rock, for it is on the sides of this protrusion, micaceous 

 at the contact with the granite, and this character ceases at two miles 

 distant from it. 3. The slates in the lias of the Alps are converted into 

 Mica Slate. Here are three Mica Slates in rocks, which are of ages 

 widely different. 



The Mica Slate of the north-east of Antrim appears to me to belong- 

 to the first type, but its age cannot be determined here, for there is 

 no base visible. Donegal is the best place in which to test its age. In 

 that county the lowest rock visible is a syenite not stratified, which 

 occurs upon the north coast, at Malin Head, at Dunaff, and at Fanit. 

 On this syenite of Malin Head lies a band of quartz rock of great thick- 

 ness, and on the quartz rock reposes mica slate, three miles wide, at 

 Glengad Head ; next comes quartz rock again, which has a general 

 dip south-east. It is a mile and a half wide along the shore, and ends 

 near Culdaff. About that village it is associated with mica slate of the 

 oldest type again, and also with gray limestone, coarsely crystalline, and 

 with greenstone protrusions, which accompany the limestone bands. 

 The dykes of greenstone are sometimes a yard, and sometimes from two 

 to four yards thick — the beds being uniform — and very persistent in 

 thickness for great distances. "What is remarkable here is, that the 

 greenstone is frequently found between limestone and mica slate, or 

 between limestone and quartz rock, as if the vicinity of lime had some 

 influence in softening the adjacent mass, when all might have been in 

 an incandescent state. Be that as it may, the repeated limestones, 

 greenstone, quartz, rocks and mica slates in the vicinity of Culdaff, un- 

 dergo many contortions. Proceeding from this village south-east along 

 the shore, or on the roads, the characteristic mica slate soon ceases : it 

 passes into a glossy slate, and then into a clay slate, at Kinnego Bay ; 

 the dip becomes more persistent and regular; the limestone ceases, and 



PEOC. E. I. A. VOL. X. 2K 



