CHAP. XIV 
LLANDEILO AND BALA ERUPTIONS OF IRELAND 
245 
Of the Chair of Kildare, has long been known to have igneous rocks asso- 
ciated with its abundantly fossiliferous Bala limestone On’ recently visit- 
in- this locality 1 found that, besides the aniygdaloidal and porphjiitic 
andesites and basalts described by Jukes and Du Noyer, the fossiliferous 
conglomerates contain pebbles of rocks like those ot the Chau, toget 
with worn crystals of felspar, while intercalated with them are thin coiiises 
of volcanic tuff. There is thus evidence here of contemporaneoim volcanic 
activity during the accumulation of the Bala group of strata. Ihe limited 
area over whicli the rocks are e.xposed, however, affords mereh a glimpse 
of this volcanic centre. , . , 
Crossing over the broad belt of Carboniferous Limestone through winch 
the Liffey flows into Dublin Bay, we come to the great continuous tract of 
older Paleozoic rocks which stretches southward to the cliffs of AVaterford. 
Through this tract runs the huge ridge of the AVicklow and Carlow^ gram e 
On the west side of this intrusive mass, hands of “ greenstone-ash, as we 
as“felspathic ashes,” have been traced among the Silurian rocks by the 
Geological Survey. But it is on the south-east side of the granite ^lat th 
volcanic intercalations are best displayed. Indeed, from A\ icklow Head to 
Dun-arvan Harbour there is an almost continuous development of igneous 
rocks risin- into rocky eminences, trenched into ravines by the numerous 
streams, and laid bare by the waves in 
eastern region, comprising the counties of 
ford that the Irisli Lower Silurian igneous rocks can best be studied. 
There are obviously various distinct centres of eruption 111 this long belt 
of country The Bathdrum and Castletimon tract forms one of these. 
Lr, o£ „,l,— s ,u KUp»«i«k Hill a “ 
southward. Arklow Head marks the position ot a third. Ihe la^as and 
tuffs which set in a few miles to the south of that promontory, and niay 
be said to extend without interruption to the south coast, were probablj 
thrown out by a series of vents which, placed along a north-east and south- 
west line, united their ejections into one long submarine volcanic bank. 
There can be no doubt that the most active vents lay at the southern end 
of the belt, for there the volcanic materials are piled up in thickest mass, 
and succeed each other with comparatively trilling intercalations of ordinarj 
sedimentary material. Some of these vents, as I shall relate m the seque , 
have been cut open by the sea along a range ot precipitous cliffs. 
The comparatively feeble character of the volcanic energy during Lower 
Silurian time over the greater part of the south-east of Ire and is showm bj 
the great contrast between the thickness of the volcanic intercalations the e 
and in Wales and the Lake country, but still more strdcmgly by innumerable 
sections where thin interstratifications of fine tuff or volcanic breccia occur 
among the ordinary sedimentary strata, and are sometimes crowded with 
Bala fossils. Some interesting illustrations of this feature are to be seen in 
the Enniscorthy district, where layers of fine felsitic tuff, sometimes less than 
' See EM^lanatioii to Qoarter Sheet 35 K.E. {Sheet 119 of ne«ei- numeration) of Geol. Survey 
Ireland (1858), p. 16. (See note, i). 206 . ) 
