GEOLOGICAL SOCIETY OF DUBLIN. 221 



the great protrusions of compact felspathic rock or of greenstone ; hence 

 all su.ch have merged in the general purple tint, lettered Ya, Yb, Yc, 

 Yd, Yf, &c, which indicates the rocks that, as a class, I have included 

 under the term " metamorphic." 



My opinion, when the examination of the districts was made, being that 

 many of the more minute strings or irregular beds of imperfectly deve- 

 loped felspathic porphyry, or even hornblendic rocks, originated in the 

 fusion or semi-fusion of a portion of the original schistose rock, during 

 the period of igneous action, when the great protrusions of the green- 

 stone and felspathic rocks took place ; and it is solely in regard to the 

 origin and nomenclature of a portion of the rocks tinted purple on my 

 Map, in which any important difference occurs between my views as 

 given on the Geological Map, and those of the Government geological 

 surveyors as represented on their maps ; and my opinions and doubts 

 on this subject are contained in my original notes, written in the year 

 1847, relating to Arklow Rock, and the igneous protrusions of the 

 country generally; and, indeed, at the present time, I entertain the 

 same doubts of the propriety of classing and uniting certain sub-crys- 

 talline felspathic rocks with metamorphic strata. But still I apprehend, 

 that too great an extension may be given by the geological surveyors 

 to a class of rocks called volcanic ash, conceived by them to have 

 been deposited contemporaneously with the formation of the rocks of 

 the Silurian period, — as I possess many specimens of apparently schis- 

 tose rocks collected within the limits of these tracts of volcanic ash, 

 which appear to me to exhibit decided indications of a sedimentary 

 arrangement, though altered in external appearance, and presenting the 

 ordinary character of metamorphic schist ; and it was this circumstance 

 which induced me to describe the districts referred to as metamorphic ; 

 many of which cannot be distinguished from the admitted metamorphic 

 schist which occurs in the vicinity of the granite boundaries of the 

 counties of Wicklow and Wexford. 



This is a subject well worthy of discussion in the field, where alone 

 a satisfactory conclusion can be arrived at. We are all searching for 

 truth, to arrive at which we have only to observe with care, and decide 

 without prejudice. 



In illustration of the foregoing observations I may mention, that 

 during the last month (May), while looking over the rock specimens 

 collected in the counties of Wicklow and Wexford during my last hasty 

 geological examination of those counties just ten years ago, and also 

 consulting my note-book, as well as the observations laid down on the 

 Ordnance Maps, for the purpose of refreshing my memory preparatory 

 to accompanying my friends, Mr. Jukes and Professor Haughton, on a 

 contemplated excursion to a portion of that district, — I discovered, among 

 other matters, a short note of my views relating to the composition and 

 structure of Arklow Rock, with the opinions I entertained at the time 

 respecting the igneous origin of the white felspathic rock, so prevalent 

 in the counties of Wicklow, Wexford, and Waterford, called by me 



vol. iv. 2 G 



