102 



Proceedings of the Royal IrisJ) Academy. 



rock, soon forms a sort of eYer-thickening porous ornst, which gradually 

 encroaches upon the sharply defined hard kernel of blue unweathered 

 rock. Concretionary structures are not common in the Bardahessiagh 

 beds ; but the so-called worm-tracks and worm -casts, which affect sa 

 many of the flaggy bedding planes, are probably due to some obscure 

 form of concretionary action. 



The Killey Bridge Beds. 



By the further diminution in the proportion of coarse material, the 

 Bardahessiagh beds pass up into the Killey Bridge beds. Like the 

 older series, the Killey Bridge beds are thought to occupy a belt of 

 country more or less parallel to the boundary of the metamorphic rocks 

 along the southern flanks of Craig Bardahessiagh ; but, unlike them, 

 they are known to outcrop at many widely separated points within 

 the watershed of the main Pomeroy river ; and as we know them to be 

 the thickest of the sedimentary divisions, it may well be that, beneath 

 the drift, they occupy the greater proportion of the Lower Palaeozoic 

 Pomeroy inlier. The best exposures are — (1) the fine section which 

 adjoins the overlap of .the Old Red Sandstone in the Little Piver just 

 south of the Slate Quarry; (2) the unnamedbrook-section between the 

 Pomeroy -Bardahessiagh road and the Slate Quarry; (3) the road-side 

 exposures south of the railway at Killey Bridge ; but characteristic 

 Trinuclei may be obtained at many other localities, and from almost 

 any of the banks where boulder-bearing drift can be obseiwed. 



As we have said, the basal members of the Killey Bridge beds are 

 practically inseparable from the Bardahessiagh beds below. Higher 

 beds, however, are much finer and softer than any, except shaley 

 partings among the flags of the lower group ; and the Killey Bridge beds, 

 as a whole, are best described as a series of calcareous or ferruginous- 

 mudstones. They, too, weather with a thick, porous, almost velvety 

 crust, and, like the highest Bardahessiagh beds, are very fossiliferous. 

 The lowest beds, as seen near Killey Bridge, or in the brook south 

 of Bardahessiagh, have alternations of coarser materials like the flags 

 below ; but upwards the bedding planes become much less evident ; 

 and the greasy character of the serpentinous paste of the older 

 beds remains to indicate the close relationship between the two. 

 The lowest partly flaggy beds abound in innumerable fragments of 

 Lamellibranchs, Gastropods, Crinoids, and Cystids. With these, also, 

 occur Phacops Brongniarti and a Calymene ; but, at the time of our 

 visit, these beds were not well exposed. 



