18 IRISH MINERALS AND BUILDING STONES. 



favourably situated and productive coal-bearing strata in the Lough Allen 

 (Arigna) area* are in the form of outliers on the tops of mountains of 

 moderate height. The beds can be traced along fairly horizontal out- 

 crops, and the strata below the Millstone Grit series are unproductive. 

 Here, then, deep mining will reveal no further source of coal. At Bally- 

 castle, however, the coal occurs in lower Carboniferous Sandstone, the " Cal- 

 •ciferous Sandstone " series of Scotland, accompanied by layers of clay-iron- 

 stone. This ironstone has been calcined on the spot, and exported for 

 smelting in Scotland. The coal-bearing strata are exposed on the steep 

 slopes, and cliffs above the shore, both west and east of the bold dolerite 

 promontory of Fair Head. They are mined by tunnelling into the face of 

 the rock ; and the dip causes the beds in some places to fall rapidly as they 

 are traced inland. The degree of folding undergone by the beds being 

 unknown as we pass south across the country, trial borings may possibly 

 reach the same strata in convenient positions away from the sea-shore. The 

 fioor of ancient schists on which the beds were deposited comes to the sur- 

 face, however, only two miles from the coast, both on the west and on the 

 south, and thus no great thickness of coal-bearing strata can be anticipated 

 as we proceed inland. We are here, in fact, limited by our position low 

 'down in the Carboniferous system, and far below the true Coal-Measures, 

 -which cannot therefore be struck by boring. 



Here and there, in the undulating country between Lough Neagh and 

 TvOugh Foyle, it is just possible that coal of the Ballycastle type occurs ; 

 but its existence in commercial quantities is extremely doubtful. Three 

 hundred years ago, as Mr. G. H. Kinahan records, ironstone nodules were 

 smelted in Drumard, near Draperstown, and they may be seen among the 

 sandstones and shaly beds in some of the stream-banks of that locality. 

 But none of the valleys that traverse these strata seems to have exposed a 

 bed of coal to view. 



The Tyrone coalfield has more promise, and provides some opportunity 

 for a prospector. The surface of Coal-Measures exposed is small, and is 

 definitely bounded by lower and unproductive beds upon the west. But, on 

 the east, the coal-bearing strata run under the Triassic Sandstone, and may 

 possibly be preserved by this covering for some distance towards Lough 

 Neagh. Considering, however, that the Trias rests on Carboniferous Lime- 

 stone in the valley of the Lagan, and also immediately south of Dungannon, 

 great denudation must have occurred during what has been termed the 

 Hercynian uplift. The Coal-Measures of Dungannon and Coalisland are 

 not at all likely to extend beneath Lough Neagh. Locally, they must be 

 regarded as rich, the Annagher seam being nine feet thick, and other seams 

 running from two feet to five feet thick. 



Efforts have been made to strike these beds on the east side of the lake ; 

 one boring was put down the neck of an Eocene volcano, the rhyolite that 

 choked the vent being mistaken for a Carboniferous Sandstone, although 

 its true character had been noted by geologists sixty years before the 

 attempt was made. Another boring was made near Carrickfergus, and 

 resulted in the fortunate discovery of rock-salt. Only by pure good luck 

 can patches of Coal Measures, if such exist, be struck by borings put down 

 through the superincumbent rocks in County Antrim. The black Silurian 

 shales of Strangford Lough have been mistaken for Coal-Measures ; but a 



* For analyses, &c., of coal of this area, see R. J. Cruise, Journ. R. Geol. Soc. Ireland, vol. 

 xlii. (1873), p. 144, and L. Studdert, ibid., p. 146. 



