520 PKOF. AV. J. PUGH ON THE GEOLOGY OF THE [vol. lxxix, 



The most important locality for fossils is the Abercwmeiddaw 

 Quarry, where the following forms have been obtained : — 



Christiania tenuicincta (M'Coy). < Cyclopyge (?) sp. (eyes). 



Harpes sp. 



Trinucleus albidus Reed. 

 Trinucleus cf. albidus Reed. 

 Trinucleus sp. 



Orthis sp. 



Plectambonites sericea, cf . var. albida 



Reed. 

 Cyclopyge rediviva (Barrande). 

 Cyclopyge armata (Barrande). 



The Abercwmeiddaw Quarry is about 400 feet above the Nod 

 Glas. 



From the Cambergi Quarry the following have been collected: — 



Brachiopod indeterminate (? Zygo- Cyclopyge subarmata Reed. 



spira). Harpes sp. 



Large Asaphid. Trinucleus cf. concentricus Eaton. 



The Cambergi Quarry is about 200 to 250 feet above the Nod 

 Glas. 



From an old trial-level on the south side of the Ceiswyn Valley, 

 about 300 to 400 feet above the Nod Glas, the following have been 

 obtained : — 



Asaphid sp. (? A. radiatus). Trinucleus cf. concentricus Eaton. 



Cyclopyge (?) sp. (eye). Trinucleus albidus Reed. 



Harpes sp. Trinucleus sp. 



Fi'om the mudstones on the north side of the Llefenni Valley, 

 I have obtained a large Asaphid, Christiania tenuicincta (M'Coy), 

 crinoid-stems, and a fragment of an indeterminate trilobite. The 

 horizon of these fossils is more difficult to determine, but it lies 

 at a maximum of probably not more than 600 feet above the 

 Nod Glas. 



The most abundant specimens are those of Trinucleus ; in many 

 cases, however, it is impossible to make a specific identification, 

 owing to the fragmentary nature of the material. Trilobite-eyes 

 belonging probably to species of Cyclopyge are also fairly common ; 

 but the main interest of the fauna lies in the discover}" of no less 

 than three species of Cyclopyge. The fauna recalls at once that 

 of the Dionide Band in the Upper Whitehouse Group at Girvan, 1 

 where the band is associated with the graptolite-shales of the 

 Dicellograptus-comp lanatus Zone . 



The Abercwmeiddaw Mudstones are about 1500 feet thick. 



Abercorris Group. 



(1) RedVei n. — The mottled mudstones of the Abercwmeiddaw 

 Group are succeeded by a group of mudstones about 350 feet 

 thick, with a well-marked rusty weathering. These mudstones 

 are tough, dark-blue, and blocky ; when highly cleaved and well 

 weathered, they are often difficult to distinguish lithologically 

 from the Cwmere Group or Lower Birkhill rocks of this area. 



1 C. Lapworth, Q. J. G. S. vol. xxxviii (1882) p. 598. 



