O'Reilly — On Jointing in Rocks about Dublin, 8fc. 145 

 XVI.— K 35° 7' E. 



XYII.— N. 46° 39' E. This direction forms the coast line from 

 Dundalk Bay to Downpatrick. It also represents correctly the direc- 

 tion of the valley of Donegal county, and contact of the granite with 

 the quartz rocks there. 



This direction, which occurs at Donabate, being extended thence 

 eastward, corresponds with the coast of the Isle of Man at Peel, and 

 forms the general direction of the southern contact thereof. 



It also represents the direction of the remarkable line of trap rocks 

 which extend from Antrim by Hed Bay, the Mull of Kantyre, the 

 south-east coast of Arran Island (Scotland), and Renfrewshire, to 

 Montrose, with the parallel band of Devonian rocks in Stirling, Perth, 

 and Porfarshire. The promontory of Carnarvon is parallel to it. 



N. 9° 27' W. This direction was noticed in the Paper of 1880 

 (p. 307 of Proceedings, 2nd ser. vol. iii.. Science). 



JN". 73° 59' W. This direction represents very fairly that of the 

 depression existing between Dublin and MuUingar, and along which 

 the Midland and Great Western Railway runs, as also the Grand 

 Canal, on whose banks, at Gollastown Bridge, this direction of joint- 

 ing is noticeable. 



XYIII. — ]Sr. 34° 39' W. This direction represents very correctly 

 the north-east coast of Ireland, from Copeland Island to Bull Point 

 on Rathlin Island. It also represents the main jointing or dykes of 

 the Mourne Mountains at the head of Carlingford Lough. Being 

 extended northwards, it traverses Iceland, parallel to the south-west 

 coast, and near Reykyavick, a point continually subject to earthquake 

 shocks. It also represents very correctly the direction of the east 

 coast of England between the Wash and the Firth of Eorth. 



XIX.— N. 25° 31' E. and K 70° 39' W. 



The direction N. 25° 31' E. corresponds fairly with that of the 

 coast line between Courtown Harbour and Wicklow Head. 



IS". 70° 39' W. This direction is that of the remarkable dykes 

 represented as occurring along the Mayo coast, between Killala Bay 

 and Broad Haven. It is further interesting as representing with 

 accuracy the theoretical Great Circle (" South boundary of the tertiary 

 formation, United States," already referred to. 



XX. — N. 53° 58' E. This direction corresponds to the line of 

 contact of the old red sandstone with the silurian at Newcastle, 

 Co. Dublin. It also represents the faults occurring to the north-east 

 of Roscrea, and to the south-west of Borris-in-Ossory ; also the direc- 

 tion of the fault occurring to the south-east of Antrim ; also the 

 general direction of the band of carboniferous limestone which stretches 

 across Ireland from Galway to Lough Neagh, and which is so markedly 



