GEOLOGICAL SOCIETY 01 LUBLIN. 123 



The second type is to be seen about Dublin, where there is a series 

 of beds of two kinds of rock, alternating with each other — one a black, 

 impure, argillaceous limestone; the other a black shale, — those alterna- 

 tions forming a passage from the gray, pure limestone into the coal shales 

 above. This is well exhibited in the railway cutting between Inchicore 

 and Hazelhatch, and also at Clontarf, both near Dublin ; it is seen in a 

 quarry at Malahow, two miles south-west of the Naul, in the north of 

 the county ; it is visible also, on the road side, one mile east of Balla, in 

 the county of Mayo, where there is a similar passage from the limestone 

 into the overlying coal shales of Slieve Corran, a millstone grit moun- 

 tain. 



In the northern type there are alternations of three kinds of rock, — 

 limestone, shale, and sandstone, — and each of the three occurs both in 

 the Old Eed Sandstone and in the limestone. There is a good section 

 in the cutting of the canal at Benburb, six miles north-west of Armagh, 

 where there are three or four bands of sandstone, and as many of lime- 

 stone and shale, in the passage from the main body of the limestone 

 upwards. 



In fossils there is a strongly marked difference between those two 

 shales. In the lower group, or Carboniferous Slate, as said before, the 

 thin beds of limestone are generally pure, and in both the limestone and 

 the shale corals and shells are abundant, and of the kinds found in the 

 limestone above ; whereas, in the upper passage, in the middle district 

 of Ireland especially, the beds of limestone are black, argillaceous, and 

 impure, and neither those beds nor the shales, with which they are asso- 

 ciated, contain any fossils, so far as I know. Above the passage, how- 

 ever, in the coal shales, fossils appear ; but the fossil mollusca of those 

 black mud beds are different from those that occur in the limestone. A 

 few species of Posidonomya, of Goniatites, and of certain Pectens, all 

 with wonderfully thin shells, as if they had lived in fresh water, are the 

 prevailing kinds, and they are not abundant, except in the beds a short 

 way above the limestone. They are found in the black shales on the 

 shore of Lough Shinny, near Skerries ; in the railway cutting at Bal- 

 dongan, near Lusk ; at Garristown, and at AValterstown, in Meath ; and 

 they are very fine at Corry, at the north end of Lough Allen, where the 

 Shannon comes into it ; also to the west of Inchiquin Lake, in Clare. I 

 may add, that I never found a Posidonomya Becheri, nor a Pecten papy- 

 raceus in the Carboniferous Slate, though I searched that band well for 

 fossils in above 150 localities in Ireland. 



Of the three foregoing types of the passage from the limestone into 

 the upper or coal shale, that one about Dublin is that with which I have 

 most to do at present, because the typical rock is one of the members of 

 the supposed calp. 



It may be interesting to remark, that in England, at the passage from 

 the limestone into the overlying coal rocks, there are three types corre- 

 sponding to those in Ireland. In Derbyshire it is the same as in Kil- 

 kenny ; in Lancashire, the same as in Dublin and Meath ; and in the 

 north of England and Scotland, the same as in Antrim, Tyrone, Mo- 



