Kinahan — On Geological Unconformabilities. 287 



Ordovician. 



The basal boundary of this group of rocks is still more compli- 

 cated. 



In the County of Dublin, and the adjoining portion of the 

 County of Wicklow, there is no actual junction seen between the 

 Bray Head rocks {Oldhamians) and the Orclovicians ; but, in places, 

 the rocks of the different groups are so near together that there is 

 no room for a basal Ordovician conglomerate, except at Moneys- 

 town Hill, near Roundwood, where a slate conglomerate seems 

 to be the basal rock. To the south, in the Carrick mountains, 

 the black Ordovician shales seem to be plastered against the older 

 rocks. 



In the Co. Wexford, near Poulshone, to the south of Courtown 

 Harbour, the black Ordovician shales are plastered against a 

 protrude of the older rocks ; while from Cahore south-eastward to 

 Bannow Bay there is no conglomerate at the base of the Ordovi- 

 cians. However, between Ballygeary Bay and Grreenore there is 

 a basal conglomerate lying on the upturned edges of the meta- 

 morphic rocks ; while the same thing probably occurs near the 

 village of Tagoat. 



Further S.W., along the south shore of the parish of Bannow, 

 there are junctions exposed. To the eastward, in the townland of 

 Ballymadden, a slate conglomerate lies on and against the older 

 rocks ; but to the westward the boundaries are very obscure, the 

 Ordovicians being plastered against protudes of the older rocks, or 

 let down among them. (See Map and Section, Geology of Ireland 

 pages 18 and 19.) 



To the west of Bannow Bay, in the cliff south of Fethard, there 

 is a slate conglomerate that lies unconformably on the strata to 

 the south. The age of the rocks to the south of this unconforma- 

 bility is disputed ; they possibly may be equivalents of portions 

 of the Welsh Cambrians, or of the Arenig group. 



If the boundaries are complicated among the unaltered, they 

 may be expected to be more so among the Metamorphic rocks, 

 which have been subjected to thrusting, faulting, and various 

 other vicissitudes. In N.W. Mayo, and Counties of Donegal, 

 Londonderry, and Tyrone, they are still in dispute. It does 



SCIEN". PROC. lt.D.S. VOL. VI., PT. V. Z 



