140 Proceedings of the Royal Irish Academy. 



IT. 12° "05 W., and, as shown, fully corresponds to that observed about 

 Dublin. The parallelism is very remarkable, and the very nature of 

 the joints in these quarries, very smooth and even, and generally ver- 

 tical, corresponds to a similar character of jointing about Dublin. 

 Similar jointing was observed in other localities about Cork. How 

 far westward it can be found present is a question of great interest, 

 and to a certain extent connected with that of the former extension of 

 Ireland to the West, since the correspondence of this direction with a 

 marked coast line implies that subsidence took place along these lines. 

 If this direction of jointing be found prevalent in the S. W. of Ireland 

 to any marked extent, there would be a fair ground for presuming 

 that the country once extended in that direction, and that successive 

 earthquakes, succeeded by subsidences, have reduced it to its present 

 configuration. That earthquakes have taken place along this system 

 of jointing in the S. W. of Ireland may in some degree be inferred 

 from the fact that a line parallel to this direction connects Cork and 

 the neighbourhood of Tuam, at both of which places earthquake 

 shocks have been felt in recent times. ITo other line would do so 

 with sufficient approximation. 



It mav be furthermore remarked that, according to the Admiralty 

 Chart of the British Isles (1879), a part of the " Yidal Bank,'' which 

 limits to the IT. W. the plateau of the British Isles, presents a lineal 

 outline having this direction, and presumably corresponding to great 

 lines of subsidence, having given rise to the great Atlantic depression 

 which commences there. 



Finally, quite recently most interesting observations as to the in- 

 timate relation existing between the jointing and earthquakes in the 

 Salt Lake territory, United States, have been made, and may be found 

 in Nature, JS^o. 732, vol. 29, p. 45 (November 8, 1883), fully bearing 

 out the connexion which I here endeavour to establish for Ireland, 

 and which gives the study of jointing such a real interest and im- 

 portance. 



II. — The second most frequent direction observed, that of 20°16'E., 

 represents the coast line between Mizen Head and Wicklow Head, a 

 portion of the Skerries coast, and the direction of the east coast of the 

 Solway Firth, between St. Bee's Head and Maryport. It is also re- 

 presented by a line joining St. David's Head, in Wales, and Braichy 

 PwU ; also by the direction of the IS". W. coast of Scotland, between 

 Buchanness and Arbuthnot. Its further extension northwards runs 

 parallel to the coast of Norway. 



III. — The third direction in order of frequency, N. 10° 34' E., is 

 not markedly represented by any part of the coast line of the eastern 

 coast of Ireland, except by the general direction between Baldoyle and 

 Skemes; but farther -"^orth in Scotland it corresponds very exactly to 

 the direction of the E. and W. coasts of the promontory of Kintyre. 



