Editing Moel Hebog (section)

===Stratigraphy===

The [[stratigraphy|stratigraphical]] sequence begins with the [[Inliers and outliers (geology)|inliers]] throughout the area. These beds consist of greenish‑grey to bluish‑grey slates with distinctive layers of [[siltstone]] locally known as "ringers". In the northern exposures, these beds also contain distinct [[quartzite]] layers, some of which are pebbly near their tops. The Ffestiniog Beds are topped by the Lingulella Band, a horizon about {{cvt|55|ft}} thick containing abundant specimens of the [[brachiopod]] species ''[[Lingulella davisi]]''. Above this, in some locations, lie the Dolgelly Beds, which contain a diverse [[fauna]] including [[trilobite]]s such as ''[[Briscoia celtica]]'', ''[[Conokephalina abdita]]'' and ''[[Parabolina]]'' species, along with brachiopods like ''[[Orusia lenticularis]]''. These fossils indicate the lower portion of the Dolgelly Beds, specifically the zone of ''[[Parabolina spinulosa]]''.<ref name="Shackleton 1961"/>

[[Tremadocian]] rocks extend into the area along the Ynyscynhaiarn [[anticline]], with the most fossiliferous exposures showing delicately striped leaden‑grey blocky [[mudstone]]s containing trilobites such as ''[[Asaphellus homfrayi]]'' and ''[[Agnostus calvus]]'' and various brachiopods. These mudstones belong to the Portmadoc Flags Formation, a locally recognised Tremadocian unit of thinly bedded, fossil‑rich mudstones and siltstones deposited in an offshore marine environment. The junction between Cambrian and Ordovician rocks remains uncertain, as many contacts appear to be [[fault (geology)|faulted]] or slipped, though the overall pattern shows Ordovician rocks overstepping Cambrian towards the north‑west, a trend seen throughout [[Caernarfonshire]].<ref name="Shackleton 1961"/>

The Ordovician sequence begins with the Pennant Slates and Quartzites, followed by the Maesgwm Slates of cleavage characterised by closely spaced, discontinuous partings that produce thin, flake‑like layers—grading upward into softer slates showing streaky alternations of dark grey and greenish‑grey material. These beds have yielded ''[[Didymograptus murchisoni]]'' and ''[[Didymograptus geminus|D.&nbsp;geminus]]''.<ref name="Shackleton 1961"/>