On the Physical Geology of the Neighbourhood of Dublin. 151 



across the end of this Upper Shale area, for which see Geological 

 Survey Explanations 102, page G2. 



The beds of this formation are in a synclinal basin, as is in- 

 variably the case in Ireland, and the low hills which they form 

 are hills of circumdenudation. This brings us to the 



Disturbance and Denudation which took place after the com- 

 pletion of the whole of the Carboniferous formation, this being the 

 third of which we have evidence in this district. Although in the 

 western and west-central parts of the Carboniferous Limestone 

 plain of Ireland the beds of that formation extend evenly and 

 almost horizontally over considerable areas, yet elsewhere they 

 have undergone disturbance and contortion. Such has been the 

 case in the district with which we are now more immediately con- 

 cerned, although by no means to the same extent as in the South 

 of Ireland. In many places the beds have steep local dips. They 

 are interestingly contorted at Loughshinny, three miles S. of 

 Skerries, evidently by horizontal compression, which has pro- 

 duced even reversed faults. They are also strongly contorted in a 

 quarry beside the bridge at Lucan and elsewhere. This disturbance 

 being greater in. the S. and S.E. of Ireland, has there produced a 

 general system of cleavage pervading all the rocks from the lowest 

 to the highest. The strike of this cleavage is in the S. about 

 W.S.W. and E.N.E.; in the S.E. it gradually turns to about S.S.W. 

 and N.N.E., and it seems to die away a little outside the southern 

 boundary of the map. This disturbance seems to have been (at 

 least principally) effected at a time earlier than the Permian age; 

 so that if, as seems most probable, no formations later than the 

 Carboniferous were laid down in this district until the Drift 

 period, the denuding agencies had nearly all the long period 

 from that time to the present in which to work their will on the 

 disturbed rocks. However this may be, they have very effec- 

 tually availed themselves of the opportunities afforded them. 



When w T e consider that the Upper Shales just mentioned, and 

 the overlying beds as far as they remain to us, are seen over 

 the greater part of Ireland, to lie in synclinal basins, and that 

 they are always remnant patches, whose limits are due to denu- 

 dation and not to the dying-out of the beds, w r e reasonably 

 conclude that these supra-Limestone beds once extended over a 

 great part of the area now called Ireland, and that they have 



since been removed by denudation. The country around Dublin 



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