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XXV. 
OK THE DIRECTIONS OE THE LINES OF JOINTING 
OBSERVABLE IN THE ROCKS IN THE NEIGHBOUR- 
HOOD OF THE BAY OF DUBLIN, AND THEIR RELA- 
TIONS WITH ADJACENT COAST LINES. By J. P. 
O'REILLY, C. E., Professor of Mining and Mineralogy, Royal 
College of Science, Dublin. 
[Read January 28, 1889.] 
Part III. 
Jointings op Bray Head and Neighbouring District. 
At the meetings of February 23, 1880, and January 28, 1884, I 
submitted to the Royal Irish Academy two Papers on the Directions 
of the Main Lines of Jointing in the neighbourhood of the Bay of 
Dublin, and their Relations with the Adjacent Coast Lines, which 
have already appeared in the Academy's Proceedings} My purpose 
was to bear out, by actual determinations, the proposition advanced in 
a previous memoir, that coast lines, in so far as regards their general 
directions, are closely related to the dominating jointings of the rock 
systems constituting these coast lines, or, in other words, that any 
given coast-line direction is made up of one or more principal direc- 
tions observable in the jointing predominant at or near the coast con- 
sidered. In these two Papers the directions recorded were mainly 
taken from the north side of the bay, and localities lying along the 
coast, so far as Skerries, and from the south side, so far as Killiney. 
The well-marked characters of Bray Head and the neighbouring moun- 
tains suggested these localities as fields of observation, and during the 
summers of 1886 and 1887 I was able to make a series of determina- 
tions of directions of jointing and of bedding, as well as of such other 
characteristics as seemed to bear upon the object of my research. 
These results I have grouped, as in the two previous Papers, so as 
to render them more directly comparable therewith, adopting with 
that view the same method of arrangement, that is : a detailed descrip- 
tion of the observed jointings and directions is first given with refe- 
rence to the localities whereat observed. 
* Vide these Proceedings^ Ser. ii.. Vol. iv., Science, p. 116. 
