PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[June 9, 



Abundance of divisional planes, having an east and west strike 

 in the form of cleavage, occur ; and the presence of them may have 



Fig. 1. — Joints {N. and S.) in the " Yellow Sandstone " and the upper 

 members of the "' Brownstones" at Ballefouloo, near Monkstown, 

 Co. CorTc. 



some influence on the absence of strike-joints among the Devonian 

 rocks in this locality. 



Jointings in the Carboniferous Limestone. — It is in the Carboniferous 

 formation, more particularly in the limestone portion, that we have 

 the features of jointing exhibited in their most perfect form. North 

 and south joints are even better developed in most of the limestones 

 than in the members of the Devonian series ; and frequently these 

 are seen so arranged that they appear cutting the limestones in such 

 a manner as to give them the aspect of vertical strata, of not more 

 than six inches in thickness each, so closely are they approximated. 

 This course of jointing, although the most prevalent, is not the 

 exclusive form in these limestones. It is well seen in the quarry at 

 Ballintemple, on the south face ; but here it does not cut up the 

 limestones into such thin masses (fig. 2) ; and in this quarry traces 

 of the original stratification can be seen, here striking E. and W., 

 and almost vertical, but with slight contortions. In general, it is 

 only in such limestones as manifest merely the N. and S. joints that 

 any information can be found as to the arrangement of the original 

 bedding. 



Besides the N. and S. jointings the limestones exhibit others, which, 

 although not so permanent, are in many instances well developed. 

 One of these is almost horizontal, but sometimes manifests a slight 

 south dip ; and this course of jointing is known to the workmen in 

 the several quarries under the name of " bedding." It is weU seen 



