630 MR. D, C. EVANS ON THE OKDOVICIAJT [Nov. T966, 



trilobites, and brachiopods occur in fair numbers. The calcareous 

 beds contain a few trilobites at the base, but graptolites are very 

 abundant throughout, even in the compact limestone. The slaty 

 black shales contain graptolites in profusion, and little else. 



(a) Prom Melin-ricket to Penlan there is only one definite area 

 occupied by the buff-yellow beds. The upward passage from the 

 AsaijJms-tyrannus Beds can be well seen at Llysonnen Quarry, in the 

 road-section north of Peny-bigwrn, Lan Quarries, Pant-yr-hendref 

 Quarry, and the road-section south of Oernant-uchaf. Fossils occur 

 at all these localities, the following being the most abundant :— 



Diplograjjtus foliaceus, Murch. 

 Climacograptus sp. 

 Dicettograptus sextans, Hall. 

 Bicranograptus ramosus, Hall. 

 Bicranograptus cf. rectus, Hopk. 

 Ogygia Buchii, Brongn. 

 Triniicleus favus, Salt. 



Orthis calligramma, Dalm. 

 Orthis testudinaria, Dalm. 

 Orthis elegantula, Dalm. 

 Lingula cf. granulata, Phill. 

 Lingula attemiata, Sow. 

 Siphonotreta micula, M'Coy. 



South-east of Castell-gorfod these beds are faulted against 

 Didymograptus-bijidus Beds on the south. Near Castell Quarry, 

 however, the A saphus- Ash and the Didymograptus-Murcliisoiti 

 Flags are brought against them by the same fault ; but a little 

 farther west they are again thrown against D.-bifidus Beds. 



Near Penlan, the main area is split into two by a thrust from the 

 north (already referred to), and in the Fenni Valley, near Melin- 

 nant-yr-eglwys, the beds are almost entirely cut out by a number of 

 faults. At IS T ant-yr-eglwys they are very much broken up by the 

 faults, which have similarly affected other beds, already described. 



From Blaensarngoch westward, as far as the neighbourhood of Llan- 

 boidy, the Dicranograjrfus-Beds occupy a well-defined area, and are 

 faulted against Didymograptus-bifidits Beds both on the north and 

 on the south. They are well seen in the low ground west of 

 Clyngwynne — around Waunfawr and Waunfach. On the road 

 near Ddol, and in Parsonage Farmyard, they are full of fossils of 

 the usual type; they are also well exposed and fossilif'erous at 

 "Wern-oleu-fach and Wern-oleu-fawr. 



In the immediate vicinity of Llanboidy they have been cut up 

 by faulting, and at Pengaerfach the outcrop is split into two 

 by a ridge of older beds. One outcrop follows that of the Asaplms- 

 tyrannas Beds in the direction of Maesgwyn-isaf, where, like the 

 older beds, they are cut off by a fault. The other outcrop occupies 

 the low ground between Wern-oleu-fawr and Frowen, stretching 

 from Pensarn Quarry on the south to Canerw Quarry on the north. 

 West of Frowen the beds run out on the ridge, as the older beds — 

 Didymograptus-MurcJiisoni Flags and Asaphus-tyranniis Ash — were 

 said to do. 



Following the northern outcrop of the Asaphus-tyrannus Ash is 

 another belt of buff-yellow Dicranograjotus-Beds, traceable from 

 Nant-yr-eglwys Mill past Maencoch, Llain, Trebleiddiau, and 



