O'Reilly — On Jointing in Rocks about Dublin, S^c. 141 



IV. — The direction 25° 30' "W. may be represented by a line drawn 

 from the centre of Lambay Island to Dunany Point. It corresponds with 

 main faulting in the Mourne Mountains, and also with a well-marked 

 line of faulting which occurs at Ballinakill, Queen's Co. ; also with 

 a Line of faulting noted as occurring to the south of Kanturk. 



V. — The direction IN". 16° 23' E., observed and remarked on in the 

 Paper of 1880, does not come out amongst those observed this year. 

 To the circumstance of its representing the coast line between Carnsore 

 Point and Wicklow Head very exactly, as noted in the Paper of 1880, 

 there may be added the fact that the Admiralty Chart of the British 

 Isles, already referred to, shows by the soundings the existence of a 

 well-marked line of depression in the Irish Sea, extending from the 

 Scilly Islands to opposite Holyhead, the direction of which very dis- 

 tinctly corresponds with that of this system of Jointing, and probably 

 represents it in its greatest intensity. 



YI. — The direction JST. 19° 31' W. represents the direction of the 

 coast between Lambay Head and Soldier's Point, at the entrance of 

 Dundalk harbour. It traverses the Mourne Mountains, corresponding 

 very closely with the direction of the two great faults which are such 

 marked features in the structure of these mountains, the one lying 

 between Silver Bridge and Belleek, and the other corresponding to the 

 line of the JS'ewry canal. Further north it represents the general di- 

 rection of the boundary of the chalk between Lough JS'eagh and Lough 

 Poyle. Its extension northwards passes through Iceland in the neigh- 

 bourhood of Vatna Jokul ; while its prolongation southwards passes 

 through the S. "W. extremity of Pembrokeshire, Launceston in Corn- 

 wall, passes between Yannes and L' Orient in Brittany, also at 

 Bayonne, and cuts the coast of Yalencia in points marked by the 

 recurrence of earthquakes. This direction is parallel to the coast line 

 great circle West Coast of Africa, which passes at Cork, and also to 

 the well-marked seismic line, which extends from the Pic du Midi in 

 the Pyrenees to Anglesea in North "Wales. 



YII. — The direction N. 5° 46' E. agrees so closely with the value 

 5° 43', found in 1880, that the same remarks as then made apply; it 

 is, however, more frequent in the district observed this year. It re- 

 presents a well-marked line of seismic action in its extensions south- 

 wards along the coast of Portugal. 



The direction JST. 49° 47' W., equally prevalent, will be found to 

 correspond with the coast line of Bray Head. This direction extended 

 passes between Woodlands and Lucan, at which latter place it has 

 been observed. Purther N. W. it corresponds with the direction of 

 the hills to the N. E. of Clonymeath river, to part of which it is 

 parallel. It is also the direction of the principal Eurite veins and 

 dykes of Killiney quarries, and further to the south corresponds to the 



