[ 443 ] 

 XL1V. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 

 [Continued from p. 856.] 



May 23rd, 1900.— J. J. Teall, Esq., M.A., F.R.S., President, 

 in the Chair. 



T^HE following communications were read : — 



-*- 1. ' The Igneous Bocks of the Coast of County Waterford.' 



By E. R. Cowper Reed, Esq., M.A., E.G.S. 



The first part of this paper is devoted to a discussion of the field- 

 evidence, as shown hy the coast-sections from Newtown Head to 

 Stradbally. The igneous rocks there exposed are divided into the 

 following five categories : — (a) The felsitic rocks ; (b) necks of non- 

 volcanic materials ; (c) the basic sills and vents ; (cZ) intrusions of 

 dolerite ; (e) intrusions of trachyte, andesite, etc. ; (/) intrusions of 

 other types. In regard to the age of the rocks, there appear to 

 have been two main periods of volcanic activity : the firs-t, in 

 Ordovician times, was marked solely by outpourings of a felsitic 

 nature; the second, post-Ordovician but pre -Upper -Old- Red - 

 Sandstone, was characterized by a succession of several distinct 

 types of igneous rocks. The lavas and tuffs, interbedded with 

 fossiliferous rocks, have been already described. These are overlain 

 by other felsites and ashes, developed near Great Newtown Head, 

 which show the same d'p and strike and partake in the same move- 

 ments. Next occurred an outburst of green and pink felsites, tuffs 

 and coarse agglomerates, developed from Great Newtown Head to 

 Garrarus ; and possibly the xenolithie felsites and greenish tuffs 

 belong to the same series. It is doubtful whether these were 

 poured out before the first folding of the Ordovician beds, but their 

 strike, when traced inland, agrees with that of the series last 

 mentioned. The intrusion of some irregular masses of felsite- 

 porphyry took place subsequently to the folding ; it was followed 

 by small veins of trachyte and andesite ; these by basic sills, 

 diabases, etc., and by a few dolerite-dykes and veins. Subsequently 

 the igneous intrusions assumed an acid character, and the felsitic 

 masses of Newtown Head, Knockmahon, etc. were extruded ; 

 probably at this time, too, were formed the isolated necks filled with 

 brecciated fragments of the earlier rocks. The felspar- porphyry 

 dykes and isolated felsitic sheets and veins which pierce the folded 

 rocks, particularly west of Kilfarrasy, probably belong to this late 

 period. 



The relative age of some of the peculiar types of intrusivo 

 rocks is indicated in the paper in those cases in which it can be 

 determined. That those rocks which are later in date than the 

 folding of the Ordovician are older than the Upper Old Red 

 Sandstone is shown (1) by the unconformity of the Upper Old Red 



