O'Reilly — On Lines of Jointing of Bray Head, 8fc. 233^ 
assuming that these lines are parallel lines of dislocation and disturb- 
ance, the centre from which this proceeded should be looked for to the 
north or south of the direction in question ; and as the dips are rela- 
tively high for the more marked jointings, it may be inferred that the 
centre was relatively proximate, and, in all probability, in the sea near 
the coast ; but it might be that the seismic undulations proceeded from 
Iceland (lying on the normal to the direction in question), and from 
the neighbourhood of Hecla, this normal being in fact one of the joint 
systems observed and recorded in 1880 (IS". 25° 52' W.). This would 
not be, as an assumption, either improbable or excessive, since it has 
been shown by Professor Judd that "Antrim, the inner Hebrides, the 
Faroe Islands, and Iceland, were, during the tertiary period, included 
in the same petrographical province," and that "this province was of 
vast extent." (See Judd, on the Gabbros, Dolerites, and Basalts of 
Tertiary Age in Scotland and Ireland, Quarterly Journal of the Geolo- 
gical Society^ vol. xlii., p. 53.) It is quite true, also, that arguing 
on the same grounds, the Carlingford district, which, according to the 
same author, " forms another great centre of eruption," may have been 
the focus of action, and the high dips of the jointings would favour 
this view. In either case, however, it is of great interest to point out 
this possible connexion between these great centres of disturbance and 
the systems of jointing in question, and in this way to bring out more 
prominently the importance of their study and careful determination. 
It may be interesting to mention here, that in Dr. Haughton's Paper 
"On the l^ewer Palaeozoic Eocks which border the Menai Straits in 
Carnarvonshire" {Journal of the Geological Society of I>uhlin, vol. vi., 
1853-4, p. 1), it is stated (p. 5), "The mean of 24 measurements of 
the strikes of the beds of limestone and sandstone through the whole 
of the undisturbed part of the district gives E. 27° IN"., or mag. E. and 
W., nearly." Now, E. 27° IN". = I^". 63° E. This direction would at 
Bray be about 62°, a close approximation to the mean value found for 
the general direction in question, K. 62° 12' E. (the value Is''. 62° 
12' E. occurring markedly and frequently on the north side of the 
Lesser Sugarloaf ). Finally, if we consider from this point of view the 
significance of the direction N. 20° 15' E., the most frequent in point 
of occurrenae of the easterly directions observed on the coast line 
studied, it may be remarked that besides showing very interesting 
relations with the lines of direction in Ireland, its prolongation passes 
through Scotland near Comrie, and runs distinctly parallel to the 
north-west coast of Norway. As in the previous Papers referred to, 
the relations between the systems observed and the general lines of 
