Fkarn SIDES, Elles, Smith — Palceozoic Rocks of Pomeroij. 105 



These Tirnaskea beds occupy the central part of a denuded 

 syncline in the Tirnaskea Stream, and have not yet been found in 

 immediate association with the overlying Llandovery, or Little Kiver 

 group ; but from the fact that the lowest beds of these closely resemble 

 the highest unfossiliferous member of the Tirnaskea beds, both being, 

 moreover, of graptolitic and presumably slowly deposited type of 

 sediment, we are of opinion that the gap between them is of small 

 importance, and that the succession is continuous. The further 

 evidence that in the beck, south of Bardahessiagh, the grits, with 

 Fhacopa mucronatus, come within ten feet of an exposure of shales, 

 with Llandovery Climacograpti in an undisturbed, though ill-exposed, 

 section, is suggestive, and tends to the same conclusion. 



The CrocJcnagargan Beds. 

 To the lowest of the Llandovery (Little Eiver group) sediments 

 we have given the name Crocknagargan beds. These are a thin series 

 of greenish-grey pyritous shales, containing few fossils, but in which 

 a few Graptolites were obtained at a locality about 100 yards east 

 of the Pomeroy-Bardahessiagh road bridge over the Little Biver, and 

 on the south bank of the stream. The species identified include 

 Cephalograptus acuminatus and Climacograptus fiormaUs, and though 

 no clear section either upward or downward can be made out, both 

 lithology and palaeontological evidence enable us to recognize close 

 similarities between this and the Cephalograptus acuminatus zone at 

 Moffat. The smooth character of the mudstone, and a certain purple 

 streakiness seen only when freshly broken rock is moistened, 

 indicate lithological affinities to the Upper Tirnaskea beds (Bicello- 

 graptus anceps zone) below, while the close approximation of the 

 micaceous shales of the Diplograptus modestus beds above, both at this 

 and at the locality of Crocknagargan itself, indicate a continuous 

 passage to the beds above. The Crocknagargan stream (south of 

 Craig Bardahessiagh) probably affords the best section of these beds, 

 but was not workable at the time of our visit. There the 10 to 15 

 feet of greenish beds which intervene between the hard grits with 

 Phacops mucronatus and the equally resistant micaceous beds with 

 Diplograptus modestus enable us to infer that the total thickness of 

 the Crocknagargan beds is not more than 10 to 12 feet. 



The Slate Quarry Beds. 

 The Slate Quarry beds are much more satisfactory, and are well 

 exposed in several places along the Little Biver, especially in its 



