TRANSACTIONS 01? THE SECTIONS. 81 



On the Geological Structure of the South of Ireland. 

 By R. Griffith, F.G.S. 



Mr. Griffith exhibited his new Geological Map of Ireland, which had 

 been constructed at the Ordnance Survey Office, Dublin, by Lieute- 

 nant Larcom, under the direction of Colonel Colby, of the Royal 

 Engineers. 



Having briefly alluded to the geology of Ireland generally, and the 

 principle which had been adopted in colouring the map, Mr. Griffith 

 proceeded to illustrate the geological structure of tlie southern counties 

 by the description of the sections, one of which commenced in the 

 granite district of Mount Leinster in the county of Carlow, and ex- 

 tended in a line nearly parallel to the south-east coast through the 

 counties of Kilkenny, Waterford, and Cork, crossing the valley of the 

 river Suir, at Carrick-on-Suir, passing over the summit of the Mona- 

 vuUagh mountains in the county of Waterford, crossing the valleys of 

 the river Blackwater at Lismore, the Bride at Tallow, and the Lee at 

 Cork Harbour, and terminated at Cork Head on the south coast of 

 the county of Cork. 



The second section extended from Brandon Head in the county of 

 Kerry in a south-eastern direction, crossing the summits of Cahirconree 

 and Carrawntoohil mountains, the valleys of Kenmare and Bantry, and 

 terminated at Gaily Head, also on the south coast of the county of 

 Cork. 



According to Mr. Griffith's views, the structure of the south-east of 

 Ireland, commencing at Mount Leinster in the county of Carlow, and 

 following the order of superposition, consists of a base of granite, on 

 which rest strata of a rock intermediate between mica slate and clay 

 slate. To the south and west of Killeen Hill, clay slate extends to the 

 base of the conglomerate ridge of the county of Kilkenny, where at 

 Coolnahay Hill, in the line of section, beds of coarse-grained red con- 

 glomerate, composed of rounded fragments of quartz, cemented by a 

 brown or reddish brown arenaceous paste, are observed to rest uncon- 

 formahly on the clay slate, which dips to the south at an angle of about 

 60° from the horizon, while the conglomerate beds dip nearly to the 

 same point at an angle of about 20" from the horizon. These conglo- 

 merate beds are identical in position and composition with those which 

 underlie the carboniferous limestone to the north of Hook Head, and 

 in other parts of the county of Wexford, which are universally admitted 

 to belong to the old red sandstone series, and, like those of Coolnahay 

 Hill, rest unconformably on old clay slate. 



The thickness of the conglomerate at Coolnahay may be about 300 

 feet. It is succeeded by beds of coarse-grained quartzose slate, and 

 occasionally of red quartz rock. 



The same succession may be tracec as far as the river Suir, where 

 the red beds are succeeded in a coniormable position by strata of yel- 

 lowisli M'hite arenaceous quartz rock, and these again by beds of greenish 

 gray imperfect clay slate, which latter rock alternates with the lower 

 beds of the carboniferous limestone of the valley of the river Suiz-, 



VOL. vii. 1838. G 



