618 ME. D. C. EVANS ON THE ORDOVICIAN [Nov. I906,. 



The road between Treasgell Gate and the top of the hill exposes 

 a continuous section in shales. Typical Bidymograptus-bifidus 

 fossils have been collected from the lower part, and the charac- 

 teristic lower B.-Murchisoni Beds are seen coming on about 

 100 yards from the top. It is worthy of remark that these upper 

 B.-bifidus Beds do not include any ash-bands. 



Shales and mudstones are extensively exposed along the lane 

 west of Treasgell, and the following fossils occur : — 



Bidymograptus bifidus, Hall. Trinucleus cf. Etheridgei, Hicks. 



Bidymograptus Nicholsoni var. Barrandea cf. Homfrayi, Hicks. 



planus, Elles & Wood. Theca. 



Bidymograptus paticlus, Hall. j Orthoceras cf. caereesiense, Hicks. 



Biplograptus dentatus, Brongn. I Lingida sp. ; etc. 



Illcenus Hughesii, Hicks. J 



The shaly mudstones in the small quarry west of Melin-castell 

 have yielded all the above, and in addition a Placoparia sp., 

 Calgmene parvifrons, Salt., and an JEglina. 



Didymograptus bifidus and fragments of several species of 

 trilobites have been collected from the mudstones on the Castell- 

 gorfod road near Efel-wen. B. bifidus also occurs farther north 

 at Mount Pleasant, and at Pensarn west of Cethin, where it is 

 associated with a Bellerophon and trilobite-fragments. 



Again, farther north near Bhydyceisiaid Chapel there are 

 numerous sections in shales. The exposures on the roadside 

 have yielded B. bifidus, Hall ; B. Murcliisoni (?) var. geminus, His. ; 

 B. JSicholsoni var. planus, Elles & "Wood ; B. patulus, Hall, or 

 B. liirundo, Salt. ; Dipiograptus dentatus, Brongn. ; Climacograptus 

 confcrtus, Lapw. ; Barrandea cf. Homfrayi, Hicks ; and Trinucleus 

 sp. These shales are cleaved, and the fossils are slightly distorted. 

 In shales at W T heel-about, Bidymograptus bifidus and a six-stiped 

 BicJiograptus have been found. 



The mudstones at Penybont and Penyback are very much 

 cleaved, and the fossils — trilobites chiefly — which occur in them are 

 hopelessly distorted and broken. Farther north and west fossils 

 become very rare. A few graptolite-fragments have been collected 

 at Cilanw, and on Felin-isa Hill. In a roadside exposure near 

 Llanboidy Bridge, however, graptolites are tolerably plentiful : 

 Bidymograptus bifidus, Hall, and B, 3£urchisoni, var. geminus, His.^ 

 occur. 



Search for fossils in the B.-bifidus Beds west of the Gronw has 

 not been attended with much success : only a few fragmentary 

 specimens of graptolites have been found. A crushed specimen 

 of B. bifidus was obtained from shales in the railway-cutting, a 

 quarter of a mile north of Login ; another of the same descrip- 

 tion in the dingle east of Maencoch-yr-wyn, and a few more at 

 Llanglydwen, a short distance from the base of the Bid 'ymograptus- 

 Murchisoni Beds. 



In the absence of fossils, the general character of the beds 

 renders them fairly easy to recognize ; besides, the ash-bands 

 which are associated with them supply useful landmarks. 



