of the North of Ireland. 153 



solid and compact, earthy and marly which vary from one to 

 three feet in thickness, and dip north-west at an angle of about 

 27°. The texture of this limestone is compact, though composed 

 of distinct lamellar concretions : it is traversed by veins of calc spar 

 of a reddish colour, and is soluble in acids without residuum : the 

 specific gravity is 2.84. It is used for building ; and the mortar 

 made from it is said to be considerably stronger than that of the 

 newer white limestone. It contains organic remains. 



At Desartmarrin in the county of Derry, ten miles to the north 

 by east of Cookstown, there is a similar shell limestone of a smoke 

 grey colour, which is also quarried. The strata dip north west at 

 an angle of eight degrees. They contain two sorts of terebratulites, 

 namely, tercbratula gigantea and terehratula producta^ and imbedded 

 nodules of a glassy quartz sometimes of the »ize of an hazel nut, 

 a circumstance that renders the blasting of this limestone with 

 gunpowder attended with danger. I was informed that at the 

 depth of seven yards, the bed of limestone is exhausted and reposes 

 on a stratum of clay, but I had no opportunity of ascertaining 

 the fact myself. 



On the south of these coal districts the limestone is yet more extensively displayed, 

 intervening between them and the northern boundary of the greywacke district in Armagh : 

 it is here exhibited skirting the banks of the river Blackvvater above Charlemont for 

 several miles ; and the country on the south and south-east between Charlemont, Loughgall, 

 Kilmore and Armagh, is principally occupied by this limestone. On the east of this 

 district near Hillsborough and Lisburn, it seems probable that the sandstone and grey- 

 wacke come into contact, the limestone being wanting : but still farther in the same 

 direction, at Cultra and Holywood, on the southern shore near the middle of Belfast 

 Lough, the limestone again appears in a position intermediate beUveeii the sandstone and 

 greywacke, but probably not in immediate contact with the latter, a red sandstone of 

 older formation being said to occur in the interval. This limestone is of the magnesian 

 variety, (which also occurs in the same formation near Dublin) its texture compact, but 

 not crystalline, its fracture granular, its colour ochre yellow : it contains cavities lined 

 with calc spar, and presents organic remains : the thickness of the beds varies from one to 

 six feet. 



Vol. in. u 



