GEOLOGICAL SOCIETY OF DUBLIN. 119 



thrown up by dislocation, or the adjacent limestone let down, and the 

 two put in juxtaposition with each other by a fault along the eastern 

 border of the sandstone, which has an approximate parallelism with the 

 adjacent shore of Lough Erne. 



Knockninny, a high, insulated, limestone hill, on the west side of 

 Upper Lough Erne, rests also on calp sandstone, which appears at its 

 western base, as shown on the " Geological Map." This is probably a 

 continuation of the Derrygonnelly band, and, like that, the equivalent of 

 the Bundoran sandstone. 



Although these three sandstones are. detached, the limestone which 

 lies above them forms to the eye a continuous range of precipices, be- 

 ginning at Knockninny, and proceeding by Ben Naghlin, Elorence Court, 

 Belmore mountain, Knockmore, Shean, Dartrey, and Truskmore moun- 

 tains, to Benbulben and the vicinity of Sligo. There is no mistaking 

 the limestone in this mountain group, for it may be traced by the eye 

 for miles before the traveller in the precipitous cliffs which abound along 

 this line, almost without interruption. The sandstones just alluded to, 

 though detached from each other, being at a fixed distance below the 

 limestone, the strata of both being parallel, their true relative position 

 also becomes known. 



From much experience and observation, I have come to the conclu- 

 sion that there is but one great group of beds of Limestone in Ireland. 

 There are intercalations in it below of thin beds of shale and thin beds 

 of limestone in the passage from the underlying Carboniferous Slate 

 into the Limestone mass ; and there are intercalations of a similar kind 

 in the passage upwards from the Limestone into the Coal rocks in certain 

 localities. But, as a general rule, I say, that in Monaghan, Cavan, 

 Leitrim, and Sligo, in Clare, Kerry, and Cork, in Tipperary, Kilkenny, 

 and Queen's County, there is but one band of Limestone. 



The second district, marked on the "Map" as calp, has been called 

 the Slievebeagh district. It is a band about eight miles wide, stretching 

 in a south-western direction between Lough Neagh and Lough Erne, by 

 Dungannon, Caledon, and Aughnacloy to Brookborough. On looking 

 over a " General Geological Map of Great Britain and Ireland," it will be 

 seen that this band is a continuation of the Carboniferous valley of the 

 Forth and Clyde, in Scotland. A district of graywacke slate and grit 

 bounds them on the south in both countries ; and, though there are 

 some exceptions, mica slate is the prevailing rock on the north all the 

 way from Aberdeen to Ballyshannon. 



This valley appears to have existed before the deposition of the Carbo- 

 niferous formation, and was a natural depression, in which that formation 

 was deposited. The S. W. strike of the valley of the Clyde is fair across 

 the channel to the county of Antrim, where the Coal rocks reappear, 

 and, no doubt, are under the Permian and chalk formations below the 

 great basin of Lough Neagh. They emerge again at Coal Island, in 

 Tyrone, and are produced thence in the same direction to Brookborough, 

 filling up the hollow between Monaghan and Clogher. It would not 

 require any great stretch of the imagination to follow this line to the black 



