Vol. 56.] IGNEOUS ROCKS OF COUNTY WATERFORD. 675 



trachytes, and some resemble closely the so-called bostonites. 

 The separation of these various types in the field is practically 

 impossible, but the examination of a large number of microscope- 

 sections has revealed their true characters. It is not improbable 

 that the}' do riot all belong to precisely the same date of intru- 

 sion : some may be slightly earlier than others, but the whole 

 group appears to be later than the felsites and earlier than the 

 basic sills, earlier perhaps than many of the felspar-porphyries. 

 The sedimentary Ordovician rocks are abundantly pierced by them, 

 but they are affected by most of the faults which traverse the 

 area, and the manner in which they are shifted and displaced by 

 them is illustrated at many points along the coast. 



At Newtown Head, Passage, several large intrusive tongues 

 and irregular veins belonging to this group pierce the bedded 

 rocks, and they seem to be of a tr achy tic nature from their 

 microscopic characters and chemical composition (see p. 685). Two 

 of these intrusions measure each from 50 to 60 feet across, as ex- 

 posed on the foreshore. The others are of smaller size, and in 

 some cases have vesicular margins. That some at any rate of these 

 are earlier than the diabase of the headland is shown by the in- 

 clusion of a portion of a vein by the latter. (See fig. 9, p. 671.) 



Between Tramore and Great Newtown Head are many 

 intrusions of this group. Some of them are of a glassy nature, and 

 have suffered contortion and crushing with the Tramore Slates. 



Two true dykes of a light- grey trachytic aspect pierce the 

 Tramore Limestones and bedded felsites, at right angles to their 

 bedding, near Doneraile Cove; and on the south side of this cove 

 is a considerable development of irregular veins of what appears 

 to be a much decomposed andesitic trachyte. A sheet of 

 similar character occurs among the felsites on the north side, 

 and a larger tongue extends over the foreshore near the base of the 

 Tramore Limestones. Of the same type are those piercing the 

 same beds near Fish Cove and above Oonagappul; but those 

 in the coves opposite Carrigaghalia penetrating the Dicrano- 

 graptus-Bhales are paler in colour, and show different microscopic 

 characters. 



The sheets in the felsitic tuffs in Waterfall Cove belong rather 

 to the trachytic andesitic type, and are of a darker colour (fig. 2, 

 p. 659). A dyke of pale-grey trachyte occurs in Lady's Cove, 

 Garrarus, and veins of a similar nature penetrate the felsitic tuffs 

 and agglomerates at the eastern end ofGarrarus Strand. A 

 peculiar banded variety is found at this spot. Several small veins 

 of a closely similar nature pierce the black slates in the middle 

 of the Strand, and are shifted by numerous small faults. The 

 vein traversing the felsite-porphyry at the western end is also of 

 this type (fig. 5, p. 662), a similarity which suggests a clue to the 

 date of their intrusion. Other irregular tongues and veins are 

 of a more andesitic type and penetrate the felsites, particularly 

 at the western end of the Strand, where they are much decomposed 

 and crushed. The original character of these rocks is obscure. 



There are several more or less distinct types of these veins in the 



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