Lower Palceozoic Rocks of the South-East of Ireland. 587 



In the fine-grained black slates of the Cambro- Silurian formation, the cleav. 

 age is sometimes carried out to such an extent as to obscure or even obliterate 

 the stratification, and it is occasionally almost equally prominent in the Cam 

 brian rocks. The cleavage, in fact, is often as fine and complete as in any slate 

 whatever, and it only fails to make good roofing slate from the want of firm- 

 ness in the material. 



It would be a very difiicult task in the S. E of Ireland to arrive at any 

 conclusions as to the relations between the strike and dip of the cleavage, and 

 the anticlinal and synclinal curves into which the rocks have been thrown, in- 

 asmuch as it is impossible, as already stated, from want of continuous sections 

 to determine those curves themselves with anything approaching to precision. 

 So far as can be observed in detached localities, it appears that there is 

 here, as elsewhere, a general tendency to coincidence in the strike of the beds 

 and the strike of the cleavage ; though if we judge by the direction of the boun- 

 daries of the areas of the formations, this coincidence seems by no means univer- 

 sal, nor, when examinedon thegreat scale, to be anythingmore than approximate. 

 The general direction of the cleavage, on the other hand, so far as it can 

 be determined by detached observations in particular quarries, coincides 

 almost exactly with the strike of the Upper Palteozoic rocks in the S. W. of 

 Ireland. 



It remains a problem for future determination, by special research directed 

 to that particular subject, whether the Lower Palaeozoic rocks were affected 

 by a slaty cleavage before the deposition of the Upper Palseozoic rocks, or 

 whether the cleavage was impressed upon both simultaneously. 



In the latter case it might have been produced by the forces which com- 

 municated the E. N. E., and W. S . W . strike to the rocks of the S. W. of 

 Ireland ; while those forces, although they thus aifected the S. E., may not have 

 been sufficient to entirely change the direction of the previously existing strike 

 of the rocks there. 



Some local exceptions, in which the strike of the cleavage runs E. S. E. 

 and W.N. W., not coinciding with the general strike of the beds, make it pos- 

 sible, perhaps, that two cleavages may have been impressed upon the country. 

 There is also the possibility to be taken into account, that subsequent 

 movements may have locally disturbed and shifted both the dip and strike of 

 the cleavage after it was formed. — J. B. J. 



