230 Proceedings of the Royal Irish Academy. 
These results are then grouped so as to give mean east and west 
directions of jointing, and, in this Paper, also of bedding; and lastly, 
these directions are discussed as regards their relations with the ad- 
jacent coast lines or other principal lines of direction manifest in the 
district. 
In order to show how far the observations detailed in this series 
accord with those given in the two Papers already published, they have 
been grouped comparatively in a special Table (facing p. 256) which 
summarizes, as it were, the whole of the three sets of the observations 
made. Prom the examination of the figures thus presented in this 
Table, it will be seen that but one new system of jointing has been 
added to those already determined — that, deducting the 73 directions 
of strikes of beds recorded in the present Paper, there remains a total 
number of observed jointings amounting to 678, which have been re- 
duced to 20 mean directions west of true north, and 17 directions east 
of true north, or altogether to 37 directions. 
It may be further inferred, that were all the jointings and lines of 
Assuring of Ireland observed and tabulated, as has been done for the 
districts studied in these Papers, they would be, in all probability, 
reducible, however numerous, to a relatively small number of mean 
east and west of true north directions, more or less frequent and pro- 
minent according to the localities and the varying physical and geolo- 
gical conditions of their structure. Prom such a mass of observations 
mean values for the different systems of directions could be arrived at 
of relatively great accuracy, and certainly closer than those recorded 
in the Memoirs of the Geological Survey, wherein for the most part 
they are given with values approximate to about 5° only, and without 
any data as to how they were obtained — whether with the aid of the 
magnetic compass, and, if so, what allowance was made for magnetic 
variation in the locality considered, at the time of observation. 
That the various systems of jointing existing in the country are 
reducible to definite systems, having not only fixed directions, but 
also marked characteristics, is one of the consequences which I con- 
sider is deducible from the results recorded in these Papers. The 
scientific importance and significance to be assigned to them would be 
proportional to the degree of their relationship with the physical and 
geological structure of the country, and, consequently, to the agencies 
having brought about that present structure. Dislocations have been 
a main cause of change, and the centres or points from which the 
forces acted having given rise to these dislocations, are fairly of the 
domain of scientific inquiry. In order to ascertain with some ap- 
proach to accuracy the positions of these centres, it is necessary to 
