108 Proceedings of the Royal Irish Academt/. 



practically identical with that of the Edenvale beds ; but with the 

 gradual diminution of the proportion of these dark bands, we pass to 

 the middle division : M. triangulatus becomes a conspicuous fossil, 

 and Climacograptus Tornquisti gradually replaces the CI. rectangidaris 

 of the lower beds. The grey, flaggy beds maintain the same 

 characteristics ; but the fossils are more sparsely distributed. Some, 

 however, of their paler grey bands now contain fossils, and are par- 

 ticularly characterized by the abundance of Monograptus acinaces with 

 M. triangulatus. In this series, also, near the head of the Edenvale 

 mill-sluice, there occur a few unusually fine examples of Rastrites 

 peregrimis. Another feature of the grey papery flags of this horizon is 

 the development of a sort of peppery sprinkling of small granular 

 concretions of pyrites. These range from about -2 mm. to 2 mm. in 

 diameter, and have a radial fibrous structure. Their occurrence in an 

 otherwise non-pyritous rock is curious, but is not uncommon in other 

 contemporaneous deposits, such as the Gigrin mudstones of Rhayader, 

 the Skelgill shales of the Lake District, and the Kastrites beds of 

 Sweden. The upper blue-grey to black banded beds again yield many 

 Graptolites, Monograptus triangulatus being particularly abundant. 

 A few Petalograpti were also observed with Climacograptus Tornquisti 

 in the less prolific beds ; and though the present authors are not 

 able to recommend the application of the three Lake District sub- 

 divisions of the M. gregarius zone of South Scotland to the Mullagh- 

 nabuoyah beds, the existence of these three sub-zones is distinctly 

 indicated. The thickness of the Mullaghnabuoyah beds is not easy 

 to estimate ; but the middle flaggy division cannot be much less than 

 50 feet in thickness, while the rest may vary between 20 and 30 feet. 

 The upper division, as seen at Mullaghnabuoyah, passes almost im- 

 perceptibly into the Petalograptus band of the succeeding Lime Hill 

 beds. 



The Lime Hill Beds. 



The Lime Hill beds are so called from the one Graptolite locality 

 known to Portlock, whence he obtained his Graptolithus Sedgwickii. 

 This locality is far distant from all those hitherto alluded to, but 

 can fortunately be correlated with them, since the lowest bed seen in 

 the Lime Hill section appears to occur also in the centre of a much 

 compressed syncline at Mullaghnabuoyah. This lowest bed is quite 

 like the topmost beds of the Mullaghnabuoyah series, but is even darker, 

 and is a banded mudstone rather than a shale ; seen at Mullaghna- 

 buoyah, it is blue-black, and perhaps three feet thick, and is 



