. Bulletin of the British Museum (Natural History), Geology. OUTCROP OF THE LOWER BALA AND HENGAE GROUPS SOUTH OF THE BALA FAULT LANUWCHLLY. ARAN VOLCANIC GROUP Fig. 1 Scale representation of sampled sections (solid vertical bars I-XII) in the fossiliferous upper part of the Lower Bala and Hengae Groups between Bala and Dinas Mawddwy. I, Gelli-grin type section. II, Maes-Meillion section. Ill, Craig y Gath. IV, Lledwyn Bach. V, Ty nant. VI, Beudy Isaf. VII, Nant Tan y Bwlch. VIII, Afon Twrch. IX, Craig Ty nant section at Rhiw March. X, Pistyll Gwyn. XI, Y Ceunant. XII, Aber Cowarch. Insets (le
. Bulletin of the British Museum (Natural History), Geology. OUTCROP OF THE LOWER BALA AND HENGAE GROUPS SOUTH OF THE BALA FAULT LANUWCHLLY. ARAN VOLCANIC GROUP Fig. 1 Scale representation of sampled sections (solid vertical bars I-XII) in the fossiliferous upper part of the Lower Bala and Hengae Groups between Bala and Dinas Mawddwy. I, Gelli-grin type section. II, Maes-Meillion section. Ill, Craig y Gath. IV, Lledwyn Bach. V, Ty nant. VI, Beudy Isaf. VII, Nant Tan y Bwlch. VIII, Afon Twrch. IX, Craig Ty nant section at Rhiw March. X, Pistyll Gwyn. XI, Y Ceunant. XII, Aber Cowarch. Insets (left, centre and right) respectively show regional setting, local stratigraphy and local geographical and geological setting. effected by the discovery of outcrops representing distal extensions of the Frondderw Ash but have also been considerably facilitated by detailed examination of the faunal succession in sections throughout the area. The stratigraphical revisions (Lockley 1980) are summarizedin Fig. 1 (inset). The Llaethnant Formation is proposed as a name for a thick group of alternating mudstones and siltstones which, in addition to representing a different facies from the stratigraphically thinner Glyn Gower Formation, is not necessarily the chronostratigraphical equivalent of that unit. The base of the Allt Ddu Formation, denned, following Bassett et al. (1966) as the base of the Frondderw Ash member, is accurately located as far south as Rhiw March in the Dyfi Valley. Similarly the base of the Gelli-grin Formation is accurately located as far south as this locality. The greater part of the Nod Glas Formation (between Aber Cowarch and Rhiw March) is shown to be equivalent to the upper part of the Gelli-grin Formation and to include the distal portions of the Cymerig Limestone member which becomes discontinuous towards the Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and ap
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