Vol. 5 6.] 



IGNEOUS ROCKS OF COUNTY WATERFORD. 



667 



Kilmurrin Cove. — In this cove there is an interesting group 

 of rocks : strongly-cleaved green felsitic tuffs, mostly of coarse 

 texture, stained red in parts, and containing numerous fragments 

 of a microgranular felsite, are pierced and overlain by veins and 

 apophyses of a diabase, which in its turn is pierced by a dyke 

 of banded felsite. Owing, however, to the unfortunate inacces- 

 sibility of the adjoining cliffs the further relations of these beds 

 cannot be determined. It is plain that they belong to a type not 

 elsewhere met with along this coast. 



Foilnaneena Cove. — At this cove, in the townland of 

 Tankardstown, we find a volcanic neck of felsitic materials, chiefly 

 fragments of the adjoining felsite-porphyry. This seems to have 

 burst through a group of earlier igneous rocks which resemble 

 trachytes or bostonites. A dyke of banded felsite like that at 

 Kilmurrin Cove cuts through all these rocks. The purplish slates 

 between this spot and Knockinahon are pierced by several sheets 

 and dykes of felsite. 



Fig. 7. — Sheet of columnar felsite intrusive 

 in light purplish slates, in the cliffs betiveen 

 Cassaunagreana Rock and Foilnaneena 

 Cove, near KnocJcmahon. 



There is also an in- 

 trusive sheet of fel- 

 site-porphyry. One 

 of the felsitic sheets 

 shows well-developed 

 columnar jointing, 

 with the columns 

 mostly straight and 

 at right angles to 

 the bounding sur- 

 faces, but somewhat 

 bent in one part 

 (fig. 7). Another 

 sheet, which is ex- 

 posed in the cliffs, 

 also forms the upper 

 portion of the pro- 

 minent stack called 

 Cassaunagreana 

 Bock. But ' the 

 finest and largest 

 sheet of felsite 

 showing columnar 

 jointing is that known as the ' Bishop's Library.' x It is at least 

 100 feet thick, and the columns, which are from four to six- 

 sided, are arranged in tiers at right angles to the bounding surfaces 

 of the sheet. It is by far the most conspicuous example of columnar 

 jointing along the whole Waterford coast. 



Knockmahon. — Near the faulted-in block of Tramore Lime- 

 stone, below the engine-house at Knockmahon, occurs a shattered 

 1 Haughton, Journ. Geol. Soc. Dubl. vol. vii (1857) p. 284. 



A = Light purplish slates, crushed and slightly 

 altered at the junction with the intrusive sheet. 



B = Felsitic sheet with columnar jointing. In one 

 place the columns are bent. 



