Mr. Weaver on the Geological Relations of the South of Ireland. 35 



river Blackvvater. Furrowed by defiles and ravines whose course is toward 

 the vale of the Blackwater,, the subjacent clayslate is exposed to our view, in 

 strata nearly vertical, supporting the sandstone formation in unconformed posi- 

 tion. The formation, as here exhibited, may be taken as a good example of 

 the old red sandstone of Ireland, and it will bear a close comparison with that 

 of England, to which it is quite analogous, presenting the same varieties in 

 colour and composition, and consisting of compact and slaty beds of firm sand- 

 stone, associated with others of a looser texture, with sandstone conglomerate, 

 and with beds of indurated clay and slaty clay ; the reddish brown colour pre- 

 dominating in the series. 



(48.) Within the ranges of the Gaultees, Slievenamuck, Slieve Riagh, and 

 Seefin mountains, clay-slate and greywacke rocks (partially traversed by small 

 veins of calcareous spar) form their foundation, in a position nearly vertical, 

 ranging from the glen of Aharlow to the westward, and upholding on each 

 side unconformable, continuous mountain masses and isolated caps of the old 

 red sandstone formation. An expansion of this sandstone spreads, on the 

 north, into the plains of Limerick, extending westward to, and constituting 

 the substance of, the three ranges of hills called Knockfeernagh, Kilcruaiff, 

 with Knockaderry, and Kilmeady ; ye^t excepting the knoll of Knockfeernagh, 

 which consists of greywacke, and greywacke slate. The sandstone of the 

 plain is generally fine-grained, and yields good flagstones in the quarries 

 adjacent to the road between Kilmallock and BrufF, where it is about three 

 miles wide, nearly horizontal, or gently undulated on the large scale, sup- 

 porting the carboniferous limestone in conformable position both on its 

 northern and southern sides, and dipping in the former 10° to the north, and 

 in the latter 20° to the south. 



In the ranges of Knockfeernagh, Kilcruaig, and Kilmeady, the sandstone is generally composed 

 of granular quartz, with interstices partly filled with white or yellowish earth (like decomposed 

 felspar) or yellow or brown oxide of iron, scales of silvery mica being sparingly scattered through 

 the mass. When the mica is more abundant, the rock takes a coarse slaty structure. When con- 

 sisting of nearly pure grains of quartz, closely compacted, it approaches to the character of quartz- 

 rock. Though associated with beds of red, indurated clay, and slaty clay, its general colour is 

 yellowish or greyish white ; but where a greater diffusion of iron oxide takes place, it acquires 

 a brownish or reddish tinge. Each range is formed of strata nearly horizontal on the top. 



tion and the magnesian limestone, as is the practice with English geologists, so as to avoid the con- 

 fusion which has arisen from its extended German signification. On the geological relations of the 

 magnesian limestone, and the subjacent red sandstone in the North of England, compared with 

 their equivalents in Germany, a clear light has been thrown by Professor Sedgwick in his admirable 

 Memoir, published in the Third Volume of the Geological Transactions, Second Series, 1829. 



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