GEOLOGICAL SOCIETY OF DUBLIN. 129 



The county of Dublin is much broken up by faults, and it is impos- 

 sible to trace the continuity of any band of rock for any considerable 

 distance. One of those faults is visible in the railway cutting at Mala- 

 hide, between the two bridges next the town. This fault has been 

 already described. A similar fault occurs at Kennon Bridge, near 

 Blanchardstown, in the cutting of the Royal Canal ; but I need not enu- 

 merate more of them. 



1. By means of those faults a certain band of light gray limestone 

 comes to the surface in many detached places. In this the beds are 

 thick and massive, and the stratification obscure. It is at Howth, Ra- 

 heny, Coolock, St. Doulough's, Portmarnock Church, Carrick Hill, be- 

 hind Malahide Castle, at Feltrim Hill, Clogran, Cappagh, in the cutting 

 of the Royal Canal near Blanchardstown, at Castleknock, Woodlands, 

 Hermitage, Curkeen, Milverton, Salmon, Oldtown, the Naul, and other 

 places. The country generally between those quarries or hills of pure 

 light gray limestone is covered by black shale, of which, in describing 

 the upper shale connected with the limestone, I have spoken already. 



2. Another type is seen in the dark gray and rather argillaceous 

 thick beds, with partings of black shale, on the sea-shore near Malahide 

 and at Swords. This is near the base, and associated with the Carbo- 

 niferous Slate. 



3. The dark gray, compact, close-grained limestone of Aclogh, near 

 Hazelhatch, in Kildare, which is brought to Dublin to be burned, is a 

 third type. 



4. The light gray fossiliferous limestone at Millecent, near Sallins, 

 in Kildare. This is much burned for lime in Dublin also. It is re- 

 markable for the abundance of fossils, and particularly of Fenestella, it 

 yields. It might be called the Fenestella limestone. 



5. The limestone at Ardbraccan, in the County of Meath ; altoge- 

 ther a crystalline gray mass, composed apparently of fragments of En- 

 crinites. This type may be seen in the front of the Royal Dublin So- 

 ciety House, Kildare- street, Dublin, and it appears remarkable when 

 viewed with a magnifier. 



6. The red limestone at Castle Espie, near Comber, in the county of 

 Down, is of another type. This band is low down in the Old Red Sand- 

 stone, but of course is a band of Carboniferous Limestone, since the Old 

 Red itself in Ireland is a division of the Carboniferous formation ; and 

 to back this, the limestone contains some of the peculiar fossils. 



7. At Armagh is a mottled marble, with a ground of brownish-red, 

 with dark brown spots softened round the edges. 



8. At Armagh there is also a brownish-gray marble, mottled with 

 black spots. 



The limestone of Armagh generally is of a yellowish-gray colour, 

 with a tint of pink through it; and this colour prevails also about Cooks- 

 town, in Tyrone. 



9. In the vicinity of Cookstown there is a peculiarity worthy of 

 notice. The whole of the limestone at this place and on to Dungannon 

 and Clogher, is much thinner than in the South of Ireland, as stated 



VOL. iv. s 



