Yol. 56.] IGNEOUS ROCKS OF COUNT! WATERFORD. 691 



no direct proof that any of the Waterford igneous rocks belong to 

 so late a period. 



It is possible that those igneous rocks which show no signs of 

 having shared in the first post-Ordovician folding are of Silurian 

 or Lower Old-Red-Sandstone date. Only certain of the felsites 

 and tuffs seem to have been involved with the Ordovician sedi- 

 mentary beds in the plication which gave them their dominant strike 

 in the South-east of Ireland (p. 660). The presence of cleaved 

 fragments of the Ordovician slates in many of the volcanic tuffs 

 and agglomerates ; the inclusion of angular chips of the surrounding 

 felsites, etc. in some of the necks ; and the manner in which many 

 of the intrusive rocks pierce through the tilted and folded sedi- 

 mentary beds, show that the consolidation, folding, and cleavage of 

 the latter had been effected before these volcanic outbursts. This 

 folding of the Ordovician beds took place presumably in Silurian 

 times, but how long it lasted is not known. If it was concluded 

 before the end of the Silurian period, some of the above-described 

 igneous rocks may be of Silurian age. The distance of the nearest 

 undoubted exhibition of Silurian vulcanicity does not seem to be a 

 serious difficulty. 



The great denudation, of these folded rocks and, so far as we 

 know, of all the igneous rocks also in County Waterford, took place 

 before the deposition of the Old Eed Sandstone; and although 

 Sir Archibald Geikie x has expressed the opinion that some of 

 the igneous rocks may be of Old-Red-Sandstone age, the evidence 

 along the coast does not favour this view. 



Prom the foregoing considerations it is evident that the time 

 during which the intrusion and effusion of imbedded igneous 

 materials took place in County Waterford is limited on one side 

 by the first post-Ordovician folding, and on the other by the pre- 

 Upper Old-Red-Sandstone denudation. This denudation probably 

 accompanied, and was a result of, the submergence of the area 

 beneath the waters of the Upper Old-Red-Sandstone lake or sea. 



Having now defined as far as possible the period of vulcanicity, it 

 is necessary to attempt to determine the succession of 

 events during that period. 



In the first place, we may remind ourselves that there was the 

 outpouring of lavas and tuffs during the Ordovician Period, and 

 these were interbedded with the fossiliferous rocks described on 

 a former occasion. 2 Then come the grey felsites and ashes near 

 Great l^ewtown Head, described in the present paper as overlying 

 these rocks and showing frequently the same general dip and strike. 

 These appear to belong to a period prior to the first post-Ordovician 

 plication, which threw the beds into a series of folds with their axes 

 running north-east and south-west. 



Next occurred the outburst of green and pink felsites and tuffs 

 and coarse agglomerates, developed from Great Newtown Head 



1 Op. tit. vol. i, p. 251. 



2 Quart. Journ. Geol. Soc. vol. lv (1899) pp. 718-71. 



3a2 



