1856.] HAUGHTON — GRANITES OF IRELAND. 193 



The following geological relations were observed by me to exist 

 among these rocks. The two varieties of granite pass into each 

 other, as may be seen in Slieve na glogh, of which the base is com- 

 posed of No. 1, and the upper parts of No. 2. At the summit of 

 this hill, the fine-grained granite, No. 2, is observed to pierce the 

 pockmarked greenstone, No. 5, in numerous veins. 



At Grange Irish, the granite. No. 2, penetrates the lower beds of 

 carboniferous limestone, which there rest upon the granite ; at the 

 junction of the granite and limestone the limestone is converted into 

 a bluish sugary marble, containing garnets, and the granite is con- 

 verted into the remarkable syenite, No. 3, composed of anorthite and 

 hornblende. 



The summit of Carlingford Mountains is composed of the syenite 

 No. 3 and the hornblende-rock No. 4, passing into each other ; the 

 hornblende-rock, however, being penetrated with numerous veins of 

 fine-grained syenite. 



The metamorphic mica-slate, of the Silurian age, which rests on 

 the north slope of Carlingford Mountain, is penetrated by dykes of 

 the pockmarked greenstone No. 5 ; and the slates, carboniferous 

 limestone, and pockmarked greenstone are all penetrated by thin 

 dykes of the grey dolerite No. 6. 



Judging from the variety and interlacing of the igneous rocks of 

 this district, there can be little doubt that it once formed the active 

 focus and vent of a most extensive volcanic outburst. 



If we suppose all the amygdaloidal or pockmarked greenstone 

 to be of the same, or nearly the same age, it must be considered as 

 post-silurian, and the oldest igneous rock in the district. The two 

 granites, the syenites, and the hornblende-rock must be considered as 

 probably of the same age and post-carboniferous ; as it will be shown 

 that the granite is converted by the metamorphic action of the lime- 

 stone into the syenite in a particular locality ; and it is highly pro- 

 bable that the whole of the syenite of the district owes its origin to 

 the limestone penetrated by the eruption of granite. The grey 

 dolerite has been observed to penetrate all the other rocks, excepting 

 the granite ; and it is probably of the same age as the latter. My 

 attention was first directed to this district by Dr. Griffith, who in- 

 formed me that it contained post-carboniferous granite. Mr. Grif- 

 fith considers the granite of Carlingford district, and also a granite 

 found near the top of Slieve Gullion in the Newry district, to be 

 newer than the granites of Mourne and Newry. It presents certain 

 structural diff'erences which distinguish it from the granites of those 

 districts*. Having described — so far as they are known to me — 

 the geological relations of the granitiform rocks of this district, I 

 shall now proceed to the mineralogical investigation of these rocks, 

 which is full of interest. 



Composition of the Granites. 

 There are two varieties of granite in this district, one composed of 



* See Journal of the Geological Society of Dublin, vol. ii. p. 113. 



