Fossil localities - Capel Curig and Betws-y-Coed. Description of 1:25 000 sheet SH 75

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From: Howells, M. F., Francis, E. H., Leveridge, B. E. and Evans, C. D. R. 1978 Capel Curig and Betws-y-Coed. Description of 1:25 000 sheet SH 75 Classical areas of British geology, Institute of Geological Sciences. (London: Her Majesty's Stationery Office.)

Map: Sheet SH 75 Capel Curig and Betws-y-Coed. 1:25 000 series - Classical areas of British geology]

Under construction

Plate 1 Caradoc Shelly fossils 1, 2 Plaesiomys multifida (Salter), x 1 Soudleyan Stage 3 Cyrtolites nodosus (Salter), x 1 Soudleyan Stage 4, 5 Dinorthis berwynensis (Whittington), x 1.5 Soudleyan Stage 6 Brongniartella minor (Salter), x 2 Soudleyan and Longvillian stages 7 Flexicalymene caractaci (Salter), x 1 Longvillian Stage 8 Broeggerolithus nicholsoni (Reed), x 1 Longvillian Stage 9 Lepidocoleus suecicus Moberg, a single plate x 4 Longvillian Stage 10, 11 Salopia globosa (Williams), x 2 Soudleyan Stage Outside the area of SH 75, some of these species range beyond the stages named here.

Fossil localities

The faunas associated with the Ordovician sediments of the district are rarely well preserved and have generally been deformed. Many localities have yielded restricted faunas of uncertain age, but good faunas have been collected from others. A selection of the latter, with lists of determinations are given below. The graptolites were identified by Professor D. Skevington and the other fossils by Dr A. W. A. Rushton# [SH 7715 5740] By track 670 m E25°S of Swallow Falls Hotel (RV 3287–3360) Bryozoa (various forms of colony), Dalmanella modica Williams, Howellites antiquior (McCoy), Kjaerina?, rafinesquinid, Sowerbyella cf. musculosa Williams, tentaculitid, Broeggerolithus nicholsoni (Reed), Brongniartella minor (Salter), Flexicalymene planimarginata (Reed), Kloucekia cf. apiculata (McCoy), tetradellid ostracod, crinoid columnals. This assemblage occurs in the Gelli Grin Calcareous Ashes of the Bala District (Longvillian Stage), except for S. musculosa which is confined to the top of the Allt Ddu Mudstoncs (upper Soudleyan). The fauna is, however, less diverse.

  1. [SH 7865 5759] Crag 180 m S18°E of Penyr-Allt Ganol (RV 6249–6256) Bryozoan, Cremnorthis sp., dalmanellid [juv.], Dolerorthis sp., Howellites sp., Nicolella sp., Paracraniops sp., Reuschella?, Sericoidea sp., Skenidioides sp. [common], Sowerbyella sp.,. gastropod and tentaculitid [fragments], Brongniartella sp. and calymenid [fragments], Lepidocoleus sp. This assemblage probably represents the Longvillian Stage but is not diagnostic.
  2. [SH 7852 5755] Crag 225 m S34°E of Penyr-Allt Ganol (RV 6257–6267) Bryozoa, Cremnorthis parva Williams [common], Dalmanella sp., Dolerorthis? [fragments], Howellites sp., Nicolella sp., Paracraniops?, Reuschella sp., Sericoidea sp., Skenidioides cf. costatus Cooper [common], Sowerbyella sp., Mimospira? [sinistral fragments], tentaculitid [fragments], calymenid and trinucleid [fragments], Lepidocoleus suecicus Moberg, crinoid columnals [circular]. The species present and the generic constitution of the fauna are reminiscent of the Gelli Grin Calcareous Ashes of the Bala District, of Longvillian age (Bassett and others, 1966).
  3. [SH 7573 5693] Forestry trackside, south of Ty-hyll (RV 6322–6361) Bryozoa [mainly encrusting], Dalmanella sp., Dolerorthis duftonensis (Reed) prolixa Williams, Howellites sp. [common], Leptestiina? [rare], Nicolella sp., Platystrophia sp., Sericoidea sp., Skenidioides sp., Sowerbyella sp. [very common], Modialopsis cf. pyrus Salter, tentaculitids, Brongniartella sp. [fragmentary], Chasmops cf. cambrensis? Whittington, Flexicalymene cf. caractaci (Salter), phacopid [fragment], Cerninella sp. [common]. Harperopsis sp. [common], Lepidocoleus cf. suecicus, crinoid columnals [pentagonal-rounded and circular]. This assemblage probably represents the Longvillian Stage.
  4. [SH 7531 5669] Trackside east of Bryn-y-Gefeiliau (RV 6444–6464) Bryozoa, Dalmanella sp. [small], Dolerorthis duftonensis (Reed) [several], Nicolella sp., Reuschella horderleyensis Bancroft s.I., Sericoidea sp., Skenidioides sp., Sowerbyella sp., triplesiid?, Cyclospira? [fragment], tentaculitid, Broeggerolithus? and cybelid [fragments], Flexicalymene sp., Lepidocoleus cf. suecicus, crinoid columnals [circular]. The fauna suggests the Longvillian Stage. The Dolerorthis includes valves resembling both D. duftonensis and D. duftonensis prolixa, both Longvillian subspecies.
  5. 6 [SH 7442 5788] Roadside exposure 400 m N13°W of Dol-gam (RV 6663–6724) Bryozoa, Dinorthis sp., Dolerorthis sp., Howellites?, Leptestiina cf. oepiki (Whittington), Nicolella sp. [abundant], Reuschella sp. [abundant], Sericoidea?, Skenidioides sp., Sowerbyella sp., Flexicalymene cf. caractaci [common], Platylichas cf. nodulosus (McCoy), trinucleid fragments, Lepidocoleus suecicus, primitiid ostracods, tentaculitids, crinoid columnals [pentagonal-rounded and circular]. By comparison with the faunas in the Bala area, a Longvillian age is suggested.
  6. [SH 7095 5789] Crags north of Llynnau Mymbyr (RV 6725–6754; 6953–6970) Bryozoan [stick-like], Dalmanella sp. [in siltstone], Dinorthis cf. berwynensis (Whittington) [in siltstone and sandstone], Howellites sp. [in siltstone], Macrocoelia sp. [in sandstone], Salopia cf. globosa (Williams) [in siltstone and sandstone]. The fauna is not diagnostic, but resembles the assemblages at the top of the Allt Ddu Mudstones of Bala (Soudleyan Stage).
  7. [SH 7865 5596] Forestry track north of Llyn Elsi (RV 7346–7373) Bryozoa [stick-like], Bicuspina spiriferoides McCoy [several], dalmanellids, Dinorthis sp. [costate], Howellites sp., Leptaena cf. ventricosa Williams, Rhactorthis?, Sowerbyella sp., Broeggerolithus [sp. indet.], pterygometopid [fragment], machaeridian [fragment], crinoid columnals. The fauna resembles that at the top of the Allt Ddu Mudstones and in the lower part of the Gelli-grin Calcareous Ashes at Bala (late Soudleyan or early Longvillian Stage).
  8. [SH 7434 5185] Crag on hillside south-east of Dolwyddelan (RV 6971–6986) Bicuspina sp., Dalmanella sp., Onniella?, Rhactorthis? [one specimen], Sowerbyella cf. musculosa?, Broeggerolithus? and calymenid [fragments], tetradellid, tentaculitid. Sowerbyella musculosa is known from the topmost Soudleyan of Bala; Rhactorthis is more suggestive of the Longvillian, but is poorly represented here.
  9. [SH 7155 5147] Crag north of Afon Lledr 290 m at 75° from Roman Bridge Station (RV 9690–9745). Bryozoa [stick-like and encrusting], Dalmanella sp. [cf. indica or modica], Howellites sp. [indet.], Sowerbyella cf. musculosa Williams [very abundant], tentaculitid, Broeggerolithus?, calymenid [fragments], Kloucekia? [small pygidium], crinoid fragments. Probably top of the Soudleyan Stage.
  10. [SH 76105119] to [SH 7610 5102] Crags between Bwlch-y-Groes and Pigyn Esgob (RV 7291–7321) Massive coarse siltstones yield: Bicuspina sp., dalmanellids, Macrocoelia sp. [large], Salopia globosa [and another form], asaphoid [fragment] and crinoid columnals. Cleaved fine siltstones yield: Bicuspina [fragment], Dalmanella sp., Dinorthis cf. berwynensis, Howellites sp., Macrocoelia [small], Cyrtolites nodosus (Salter), crinoid columnals [round and pentagonal-rounded]. Soudleyan or possibly Longvillian Stage.
  11. [SH 7800 5926] By roadside at Llyn Sarnau (RV 3475–3507) Amplexograptus arctus Elles & Wood, A. fallax Bulman, A.? perexcavatus (Lapworthl ?Climacograptus antiques bursifer Elles & Wood, ?C.brevis Elles & Wood, C.lineatus Elles & Wood, C.minimus (Carruthers), ?Glyptograptus euglyphus (Lapworth), G.siccatzis Elles.& Wood, Orthograptus ex gr. calcaratus (Lapworth), O. ex gr. truncatus (Lapworth). Zone of Diplograptus multidens.
  12. [SH 8000 5870] Roadside exposure, 0.5 km N of Cwmlanerch (DT 7732–7742) Amplexograptus sp., Climacograptus ?brevis, C. cf. brevis, C. lineatus, ?Glyptograptus euglyphus, Orthograptus ex gr. calcaratus, O. ex gr. truncatus, Pseudoclimacograptus ?scharenbergi (Lapworth). Zone of Diplograptus multidens.

References

Glossary