612 MR. D. C. EVANS ON THE ORDOVICIAN [Nov. I906, 



slickensided slabs have been dug up about the middle of the quarry, 

 and south of this spot the following fossils occur : — 



Didymograptus extensus (?) Hall. 

 Didymograptus pen?iatulus, Hall. 

 Didymograptus patultcs, Hall. 

 Tetragraptus serra, Brongn. 

 Tetragraphis quadribrachiatus, 



Hall. 

 Ampyx cf. Salteri, Hicks. 

 JEgliiia caliginosa, Salt. 

 Mglina cf. boia, Hicks. 

 Trinucleus sp. 



Agnostics sp 



Lingula. 



Obolella. 



Palesarca. 



Comdaria margaritifera, Salt. 



Comdaria cf. Homfrayi, Salt. 



Tlieca sp. 



Caryocaris sp. 



Orthoceras sp. ; etc. 



North of the break there is a slight lithological difference, and 

 the fossils indicate a higher horizon, probably the higher beds of 

 the TetragraptusSeries. The following fossils have been found ; — 

 Diplograptus dentatus, Brongn. ; Climacograptus confertus, Lapw. ; 

 Plaeoparia cambrensis, Hicks ; and a few fragments of extensiform 

 graptolites, but no Didymograptus bifidus. The roadside-sections 

 have yielded Didymograptus cf. extensus, Hall; D. patidus, Hall; 

 Tetragraphis serra, Brongn. ; Comdaria sp. ; Beller •ophon multi- 

 striatus, Salt. ; and an Orthoceras. 



Extensiform graptolites have been collected from the mudstones 

 in the watercourse south of Bwlchydommen. JEglina and other 

 trilobite-fragrnents also occur here, near the junction of the 

 Tetragraptus-I>eds and the Didgmograptus-bifidus Beds. 



The dips here strongfy suggest an inversion due to overfolding 

 or faulting — probably to both. The crushed state of some black 

 shales seen in a ditch west of Sabulon, and the watery condition of 

 the ground near by, confirm the suggestion as to the occurrence of a 

 fault. 



The mudstones in Gors farmyard have yielded some isolated 

 Tetragraptus-stiipes, and the exposures about Pwlltrap contain few 

 fragments of Dendrograptus and JEglina. A Dictgograptus was 

 obtained from a well at Ostrey, and fragments of Didymograptus 

 Jiirundo, Salt., from the mudstones in the bed of the Gynin close by. 

 Some fragments of extensiform graptolites have been collected from 

 the crushed mudstones at Melin Cleifon and the railway-cutting 

 near St. Clear's Station. JEglina also occurs at the latter place. 



A small opening in shales at Parkyrabat and the roadside- 

 section near Castell-y-waun have yielded graptolites of extensus-type. 

 The latter locality has, in addition, yielded a crushed specimen of 

 Tetragraptus cf. quadribrachiatus, Hall; Didymograptus extensus (?) 

 Hall ; and tails and eyes of JEglina have been collected from the 

 mudstones of the railway-cutting north of Banc-y-felin. 



Near Llainlwyd, a mile north of St. Clears Station, there is a 

 good road-section in shales. These are fairly fossiliferous at certain 

 points. At the lowest end of the section the beds are nearly vertical 

 and barren, but ■ at the turning in the road higher up extensiform 

 graptolites occur, which are usually very fragmentary. Half way up 

 the hill the following have been collected : — 



