1858.] HAKKNESS JOrN-TINGS. 97 



matters for comparison are the induration of the rocky masses, and 

 the superinduced structure, slaty cleavage, which occurs in such rocks 

 as are not highly calcareous. With reference to the appearance of 

 joints in these rocks anteriorly or posteriorly to their induration, it 

 may be observed that the evidence as to the age of jointing relative 

 to these conditions, most strongly supports the conclusion that joint- 

 ing has taken place after the consohdation of the rocky masses. 

 Fossils are in many instances cut through by the joints ; and not 

 only fossils, but in some portions of the South of Ireland, as in the 

 county of "Waterford, and at Mount Misery on the east side of the 

 Suir, immediately opposite to the town of Waterford, coarse conglo- 

 merates, containing quartz -pebbles, are intersected by joints which 

 cut the quartz-pebbles as clean as if a lapidary's wheel had been the 

 instrument effecting this cutting (see Sir H. De la Beche's 'Geological 

 Observer,' p. 628) ; a circumstance, which it is difficult to imagine 

 could have taken place had these pebbles been in the condition of 

 loose fragments imbedded in soft sand. 



The great regularity which prevails among the joints, and the 

 parallelism which exists among members of the same series, are also 

 antagonistic to the supposition that this structure affected rocks an- 

 teriorly to their consolidation ; and indeed the whole features which 

 pervade these divisional planes, are more favourable to the conclusion 

 that jointing has affected rocky masses subsequent to their consoli- 

 dation. 



Concerning the relative age of the jointing and the slaty cleavage 

 which is so common and well- developed in the Devonian rocks of 

 the county of Cork, some information is afforded by the deposits of 

 this age ; and, as the same series of N. and S. joints are common to 

 both the Devonian and the Carboniferous strata, the deductions which 

 can be obtained from the former equally apply to the principal joints 

 of the latter. On the surfaces of the cleaved strata, that rugose 

 appearance which frequently presents itself on such surfaces, is very 

 apparent, and has somewhat of the aspect of ripple-markings. Joints 

 cut across these rugose surfaces, in such a manner as to show that the 

 roughened structure was not induced subsequently to the formation of 

 the divisional planes ; as the joints intersect and separate what would 

 have been continuous ridges and hollows, but for the interference ot 

 the jointings ; leading to the conclusion that this rugose structure, 

 the result of cleavage, existed anteriorly to the intersection of the 

 rocks by joints. There is another feature, in connexion with cleavage 

 and jointing, which still further supports the inference as to the 

 posterior age of joints. This is the smooth nature of the sides of 

 the latter ; for, had they existed anteriorly to the cleavage, in an 

 approximated condition, such as that in which they now present 

 themselves at many spots, it would be difficult to conceive their 

 retaining the smooth character of their sides ; since the force which 

 gave rise to cleavage, and which caused the extension of the mineral 

 matter of the rocks in the direction of the cleavage-planes producing 

 the rugose structure, would have produced a like structure on the 



VOL. XV. PAET I. H 



