1858.] 



HAEKNESS JOINTINGS. 



95 



shales, the latter highly indurated. On the north side of this quarry, 

 the beds, consisting of gritty rocks dipping N. at 60°, are iatersected 

 by N. and S. joints, nearly vertical, but in some cases inclining 

 somewhat to the east. 



These N. and S. joints are, on the whole, remote from each other, 

 and they are the only series which make their appearance in the 

 gritty strata here. On the south side of the quarry, beds of a more 

 shaly character occur, having the same inclination as the grits on 

 the north side. Here, however, the jointing is much more complex ; 

 and, as the thin shaly strata vary in their mineral nature, with 

 every variation we have modifications in the jointings. On one bed 

 of purple shale, fine in grain, the N. and S. joints are seen in close 

 proximity, but having a shorter course than in the gritty strata ; and 

 in a layer of fine drab-coloured shale, which lies about 9 inches below 

 the shale with the closely approximated joints, systems of jointings 

 occur as complex and as perfect in their arrangements as any which 

 make their appearance among the Carbomferous limestones of Cork, 

 but without effecting that obliteration of original stratification, which 

 is an attendant on the complex series of jointing in the limestones. 

 The complex series of joints pervading the fine drab shales at Clunnie 

 quarry have their planes so approximated that hand-specimens afford 

 very perfect examples of these planes ; and an example is here figured 



with three distinct, well- 

 Fig. 9. — A. piece of Jointed drab- marked series of jointing- 

 coloured Shale, from Clunnie planes, having a disposition to 

 Quarry, Troqiieer, KirJccud- cut the shale into a succession 

 bright. Half nat. size. of rhombs (fig. 9) ; and this 



example makes it manifest 

 that mineral matter totally dif- 

 ferent in its nature from lime- 

 stone has, from the forces which 

 produce jointing, assumed an 

 arrangement in its divisional 

 planes which, in most respects, 

 agrees with those of the purer 

 limestones ; but in the shale, if 

 more minute jointings can be 

 regarded as indicating a higher 

 development of the force pro- 

 ducing this structure, we have a 

 complex mineral structure ex- 

 hibiting more perfect joints than 

 even an almost pure carbonate of lime. 



The threefold Jointings near Cork. — In the allusions which have 

 been made to the three forms of jointings which are common to the 

 limestones of the district around Cork, it is by no means intended to 

 convey the idea that, in all instances where the threefold series 

 occur, one is vertical, having a N. and S. course, the second hori- 

 zontal, and the third oblique, inclining at an angle of 45°. These 

 can only be regarded as the typical modes of occurrence and the 



