188 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 6, 



supposed to lie on the geological horizon of the Lingula-beds of Wales ; 

 and it is older than the calp-deposits of the carboniferous limestone 

 of the county Dublin, as is proved by the latter, as at Crumlin, 

 county Dublin, containing angular fragments of the granite of the 

 potash-type in question. 



The soda-granites of Wicklow and Wexford also are subsequent to 

 the same Silurian rocks of these counties, as they convert the latter, 

 when in contact with them, into hornblende- and mica-slate, and 

 exhibit the usual phenomena of metamorphic action, such as the 

 development of minerals. — S. H. 



Trinity College, Dublin, March 3, 1856. 



PART II. — On the Granites of the North-east of 



Ireland. 



Introduction. 



I. Granite of the Mourne District. 



Elementary Minerals. 



Accidental Minerals. 



Composition of the Mourne Granite. 



II. Granites of the Carhngford District. 



Description of the Igneous Rocks of Carlingford. 

 Composition of the Granites. 

 Composition of the Syenites. 

 IIL Granites of the Newry District. 

 Potash-Granites. 

 Soda-Granites. 



The granite-rocks of the north-east of Ireland are mostly collected 

 into a limited district on the borders of the counties of Down, Louth, 

 and Armagh. This district contains all the granites of the north- 

 east of Ireland, with the exception of a small outburst near Cushun- 

 dun in the county Antrim, of which separate mention will be made. 

 The granitic district of the north-east of Ireland admits of sub- 

 division into three natural groups. 



1st. The granite-district of Mourne; which consists of a nearly 

 circular mass of granite, having a diameter of about nine miles, lying 

 to the north of Carlingford Bay. 



2nd. The granite-district of Carlingford, which is also nearly 

 circular, having a diameter of nearly five miles, and lying to the south 

 of Carlingford Bay. In this district, in addition to the granite proper, 

 there is much hornblende-rock and syenite, with varieties of green- 

 stone, the exact relations of which to the granite have never been 

 precisely ascertained. 



3rd. The granite-district of Newry, extending from Slieve Croob, 

 on the north-east, in a south-westerly direction to Forkhill and 

 Jonesborough, a distance of twenty-eight miles, and having an 

 average breadth of six miles. 



I. Granite of the Mourne District. 



Elementary Minerals composing the Granite of the Mourne District . 



The granite of the Mourne mountains is very fine-grained, and 

 contains numerous vughs or cavities, which are lined with distinct 



