Mr. Weaver on the Geological Relations of the South of Ireland. 55 



11. Carboniferous Series in North Munster. 

 In Clare, and extending into Galway. 

 Old Red Sandstone. 

 (69.) This formation, in the district under consideration, is quite analogous 

 in composition, structure, and position, to that observed by me in other quar- 

 ters of Ireland. Its chief mass extends from Derrybryan mountain, on the 

 north, to Lough Derg on the south-east ; but from near Lake Youlky on the 

 west, it is continued to the south and east in a narrow belt, encircling the 

 clayslate mountains, and reposing, wherever the contact is observable, in un- 

 conformable position ; in the higher grounds, in nearly horizontal strata, but 

 on the flanks declining according to the declivity. This may be conveniently 

 observed in the hills lying north of Limerick ; and at six miles from the city 

 on the road leading both to Broadford and Killaloe, where the sandstone 

 rests in horizontal strata on the vertical edges of clayslate (the latter ranging 

 east and west), but nearer the vale, the former rock dips toward the 

 south, under angles of 23° and 20°, and the succeeding limestone is in cor- 

 responding position, yet in receding, approaches to an horizontal arrange- 

 ment. These relations are also observable in the strata extending to the 

 west past Crogh an ambry dy mountain. To the north, Derrybryan moun- 

 tain, consisting wholly of this formation, exhibits horizontal beds in the higher 

 lands, but inclined on the flanks. Thus, in proceeding west toward Gort, 

 the sandstone strata are inclined 30° and 25° westward, and the succeeding 

 limestone, where first apparent, is in conformable position, but more west it 

 gradually becomes horizontal. In Derrybryan mountain may be found aU the 

 common varieties incident to the old red sandstone, including beds of red, in- 

 durated clay, and sandstone conglomerate. The latter rock appears occasion- 

 ally in considerable force, containing, in places, rounded and angular ingre- 

 dients as large as turkey's eggs ; and from its mottled aspect, resembles 

 strongly the sandstone conglomerate north of Waterford bridge, and of the 

 Drumdowney quarries adjoining the Barrow and the Suirc*. 



Carboniferous Limestone. 

 (70.) The general tendency of this formation to a nearly perfect, horizontal 

 arrangement, as extending from the county of Galway into and through that 

 of Clare, is remarkable, the deflections from that position being only inci- 

 dental and seldom important. Undulations on a very large scale occur, yet 

 rarely varying more than a few degrees from the horizon. The chief lines of 

 elevation are adjacent to the old red sandstone. This disposition is wefl de- 



* Geological Transactions, First Series, vol. 5; Memoir on the East of Ireland, §. 149. 



