238 



also the greenstone, and in this character it continnes towards Innish- 

 owen Head. From near CuldafF, by Kinnego, the clay slate and grit have 

 a persistent dip to the south-east for three or four miles, so that the 

 thickness of this system must be very great. Four miles, dipping at 

 45°, would give about 15,000 feet. Since there are no fossils known 

 in this great mass of slates and grits, I take it to be the equivalent of 

 the Cambrian rocks, and the whole of it lies over the mica slate of Cul- 

 dafF, and is, course, newer than it. From this statement it may be un- 

 derstood that quartz rock is the oldest stratified rock known in Ireland, 

 and mica slate, with its associated limestone, &c, the second eldest. 



The mica slate near Culdaff is characterized by containing beds of 

 crystalline limestone, as just stated. The case is exactly similar in the 

 extensive mica slate district, between Dungiven and Derry; in which 

 generally the dip approaching Derry is N. W. } the reverse of what 

 it is at Culdaff, suggesting the idea that it passes in a synclinal 

 band under the Innishowen clay slate mountains. Another small 

 district of mica slate, lying to the west of the road from Garvagh to 

 Maghera, has many quarries of gray crystalline limestone, from which 

 it is raised and burned for economic use. 



Mica slate, is the lowest rock on the Derry side of the basaltic area 

 also, but there it is vastly more extensive than in Antrim. The whole 

 breadth of the county to the west of Dungiven is mica slate, from the 

 county boundary at the top of Sawel, a mountain 2236 feet high on the 

 south, to Ballykelly on the north, near the shore of Lough Foyle, a dis- 

 tance of 15 miles. The general dip of the rock the whole way from 

 Sawel to Ballykelly is to the north, at angles varying from 25° to 45°. 

 Unless there may be parallel faults in an east and west direction through 

 the country, by which the same groups of strata might be counted over 

 and over, the thickness of the mica slate on this, which is nearly a 

 meridian line, is very great; for 15 miles, with an average dip of 35°, 

 would give it a thickness of 45,460 feet. Of the mica slate of the 

 Knocklayd district, upwards of two-thirds of it belongs to the talcose 

 variety, the other one-third to the common, or that which contains a 

 large proportion of quartz, and a small amount of mica. The cliffs of 

 Cushleak, on the coast between Glendun and Murlogh bay, present 

 mica slate, containing subordinate beds of primary limestone, with veins 

 or dykes of syenite, and of felspar porphyry. Several veins of reddish 

 brown felspar trap are found also on this coast, and are seen inland on 

 the old road from Cushendun to Ballycastle. The limestone at Tor 

 point is about 50 feet thick ; in colour it varies from gray to reddish 

 gray, and greenish gray. The texture passes from compact to granu- 

 lar. It is intersected by thin veins of calcareous spar. Hornblende 

 slate is found in the valley of Glendun, and also in many places along 

 the coast, in the mica slate. Granite was found by Sir Richard Griffith 

 on the coast at Castle Park, half a mile north-east of Cushendun, and 

 at Ardsillagh on the mountain side higher up. I shall make allusion 

 to this granite in another part of this paper. 



