232 
Proceedings of the Royal Irish Academy. 
therefore, not be excessive to pretend that a magnetic survey of 
the country, or, indeed, of any other, should, to a certain extent, 
be brought into relation with the main lines of faulting, and that, 
consequently, a correct determination of these and their proper co- 
ordination should precede, and, as it were, mark out the ground for 
such a survey. 
Assuming, as has already been advanced, that there is a direct 
relation between the systems of lines of dislocation of this country 
and the centres of seismic disturbance whence proceed the undula- 
tions or shocks which gave rise to them, it may be of interest to 
examine, from the data collected in the summaries accompanying this 
Paper, some very suggestive indications which they present. 
Thus, it may be remarked, that for the district observed north and 
south of Dublin Bay and surrounding country the systems of west 
jointings— (I.) 14° 39' W., (II.) 20° 8' W., and (lY.) 28° 33' W. sub- 
tend Iceland to the north, while their prolongations to the south cut 
the Pyrenees in those points of the chain the most frequently shaken 
by earthquakes in modern times, that is, the portion of the chain which 
lies between Foix and San Sebastian, of which the Pic du Midi would 
be about the centre. Assuming that the centres of seismic action hav- 
ing given rise to these dislocations should lie on normals to these direc- 
tions, they should be found either to the east or to the west of these, 
and therefore in the direction of the Atlantic or of Great Britain ; as, 
moreover, the dips of these west jointings are for the most part nearly 
vertical, it might be inferred that the source of action is proximate, 
and probably to the eastward, and in the channel, or connected with 
the seismic centres of Great Britain. 
Taking another direction, that of I^. 64° 16' E., it maybe observed 
that it represents distinctly the direction of the southern coast line of 
Ireland, to which occur parallels at different intervals to the northward. 
Examining these, as laid down on a map of Europe, such as that of 
Stanford (and noting that the direction already cited, IS". 28° 33' W., 
is nearly normal to it, and cuts Iceland between Eejkiavik and Hecla), 
it will be observed that this southern coast line of Ireland direction 
being produced crosses Great Britain and Denmark, and touches the 
southern part of Scandinavia near Christianstadt, running thus nearly 
parallel to the coast line of Holland and Korth Germany, between the 
Texel and the Gulf of Dantzic, while a parallel to it, running along 
the north coast of Antrim, intersects the south point of Norway, and 
runs parallel to the south coast of the Gulf of Finland, so noted for 
the disturbances which the magnetic needle there undergoes. Now, 
