O'Reilly — On Jointing in Rochs about Dublin Bay, 8fc. 307 



tion, it has nearly the same interest, and passes through the same 

 countries nearly, as the direction 16° 23'. 



The only other directions to which attention may be more particu- 

 larly called are the dii-ections 89° 45' W. ; 9° 27' W. ; and 5° 45' E. 



The direction 89° 45' W. is represented at Dublin by the jointing 

 in the granite rocks which occur at Blackrock, and which are the most 

 northerly outcrops of the rock. Its continuation across Ireland, from 

 that point, brings it out at Galway, and there corresponding with 

 certain portions of the granite coast line. It represents the line of 

 least elevation crossing Ireland from east to west, and is roughly 

 represented farther south by the line which would pass from Camsore 

 Point to the Great Blasket Islands. It may be taken as the direction 

 of the axis of the Liffey valley. 



The direction 9° 27' "W. represents fairly the coast line between 

 "Wicklow Head and Dunany Point, in the Co. Louth; and its con- 

 tinuation passes through the Mourne Mountains, along a portion of 

 the west side of Lough ITeagh, and comes out on the coast of Antrim, 

 near the promontory of Portrush. The angle of 40° with this gives a 

 direction which corresponds very closely with that of the Caledonian 

 canal, while the direction 70° with the canal takes in Pifeness, Bam- 

 borough Head, and the coast line between Foulness and Yarmouth. 



This same direction, 9° 27' W. 



gives with the direction, 30° 08' E. 



(so remarkable at Ireland's Eye), an intersection of 39° 35' 



Lastly, the direction 5° 43' E. represents the portion of the coast 

 line between Baldoyle and Ptush ; but more particularly represents 

 the direction of the Great Circle which I had traced, a priori, on the 

 globe as the " TFest Coast of Portugal,^'' and which is represented 

 by well-marked faulting in three or four places, by hill direction, and 

 by the east side of Pathlin Island. 



As regards the eastern coast of Ireland, it may be fairly advanced 

 that it is represented by directions which correspond to lines of joint- 

 ing observable, in greater or lesser number, about the Bay of Dublin, 

 and which are as follows : — 



Prom Carnsore Point to Wicklow Head, . . . 16°25'E. 



„ Wicklow Head to Clogher Head, . . . . 9° 27' W. 



,, Bellagan Point, Carlingford Lough, to \ ^„o oa/ -p 

 John's Point, Dundrum Bay, . . j ' 



,, Donaghadee to Bruce's Castle, Eathlin Is., 29° 11' W. 



The three last directions are not the more frequently occurring in the 

 Bay of Dublin, but do occur. It should be noticed that the direction 

 48° 30' E. is almost exactly that of the line of porphyritic rocks so 

 markedly characterising the geology of the county Wexford. 



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