610 MR. D. C. EVANS ON THE ORDOVICIA.N [NOV. I906, 



of the Didymograptus-extensus type. The beds are probably the 

 same as those exposed north of Talvan. 



About three-quarters of a mile to the west the same beds are 

 seen in some roadside-sections. That near lihydywrach has yielded 

 Didymograptus extensus, Hall; Tetragraptus serra,l&xongn.; JEqlina 

 sp.; Obolella sp., etc. There is some obscure faulting in the locality, 

 for immediately to the south are Didymograptus-bifidus Beds, which 

 appear to dip under Tetragrap>tus-Beds. Also, at a short distance 

 to the north, there are shales of D.-bifidus type. 



The B,hydywrach stream, to the south, has cut through shales 

 and mudstones at several points. Fossils have been collected in 

 these, which fix their age as Upper Tetragraptus; and their general 

 strike and dips suggest that they pass up into higher beds in the 

 immediate vicinity. 



In the railway-cutting north of Llanfallteg Station are seen good 

 sections in Tetragraptus and Didymograptus-bifidus Beds, with a 

 fair abundance of characteristic fossils. The dips at the southern 

 end of the section suggest a small anticlinal fold showing Upper- 

 Tetragraptus passing up into Didymograptus-bifidus Beds. The 

 former here contain a fair abundance of Diplograptus dentatus, 

 Brongn., and Climacograptus confertus, Lapw. : Didymograptus 

 patidus, Hall ; D. hirundo, Salt. ; but no D. bifidus. Trilobites 

 also occur, including Barrandea sp., jEglina binodosa, Salt., and 

 jEglina sp. ; and Comdaria, Theca, and Ortlioceras have been 

 obtained. The beds in this section have been disturbed by 

 several faults — probably the westward continuation of Rhydywrach 

 conditions/ 



North of the small dingle (the southernmost of the two) the beds 

 have yielded the following fossils : — 



Dendrograptus sp. 

 Schizograptus sp. 

 Didymograptus extensus, Kail. 

 Didi/mograptus patulus, Hall. 

 Tetragraptus serra, Brongn. 



Tetragraptus quadribrach iatus, 



Hall. 

 JEglina sp. 



Trinucleua Sedgwickii, Salt. 

 Lingulella sp., etc. 



The same series of beds — mudstones and shales — are exposed at 

 intervals along the railway near Gwarmacwydd, and continue north- 

 wards as far as Login, but are very sparingly fossiliferous. Even 

 where fossils occur they are not easy to find, and then to identify, 

 owing to cleavage. 



There is a continuous section up Penclipin Hill and down Mount- 

 Pleasant Hill, in both of which fossils are exceedingly scarce. The 

 beds at Mount Pleasant are more arenaceous than the usual type, 

 are badly cleaved, and have not yielded a trace of fossils. These 

 beds are also exposed about Bryntaf and Penyrallt. 



East of the Gronw at Glandwr, near Pantygrug, there are several 

 exposures of graptolitiferous shales and mudstones, which have 

 yielded Didymograptus extensus, Hall ; Tetragraptus quadribra- 

 chiatus, Hall ; T, Bigsbyii, Hall ; Schizograptus sp. ; JEglina sp. ; 



