. Bulletin of the British Museum (Natural History), Geology. ARENIG OF CARMARTHEN DISTRICT 235 CWM YR ABBEY 50 metres. Fig. 5. Outcrops of Arenig rocks in Allt Pen-y-Coed and Cwm yr Abbey. over 1 m, generally separated by an equal or slightly greater thickness of black mudstones or shales; the Member is about 70 m thick. The turbidites are generally well graded, with quartz and feldspar clasts in a dark siliceous matrix. Towards the mid-part of the Member the turbidites greatly increase in thickness at the expense of the intervening shales; the 2 m thick graded units in this part of the sectio
. Bulletin of the British Museum (Natural History), Geology. ARENIG OF CARMARTHEN DISTRICT 235 CWM YR ABBEY 50 metres. Fig. 5. Outcrops of Arenig rocks in Allt Pen-y-Coed and Cwm yr Abbey. over 1 m, generally separated by an equal or slightly greater thickness of black mudstones or shales; the Member is about 70 m thick. The turbidites are generally well graded, with quartz and feldspar clasts in a dark siliceous matrix. Towards the mid-part of the Member the turbidites greatly increase in thickness at the expense of the intervening shales; the 2 m thick graded units in this part of the section include feature-forming conglomeratic beds. Fossils are confined to the interbedded argillaceous rocks and are usually flattened. Pyritic 'ghosts' of trilobites are frequent. When poorly preserved, cranidia of Bienvillia praecalva sp. nov. are easily confused with those of Porterfieldia punctata (Crosfield & Skeat); discovery of the spinose free cheeks of the former. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original British Museum (Natural History). London : BM(NH)
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