Stapeley Hill

The area of Stapeley Hill is unenclosed common land crossed by numerous paths and a bridleway linking it to the Mitchell’s Fold Stone Circle. Convenient parking places are therefore either the visitor’s car-park for the Stone Circle or by the chapel at the start of the hamlet of White Grit on the Priestweston road. From the latter is 400 m by paths which will lead to the quarry which best exposes the volcanic rocks for which this site is famous and from which the following short trail can be followed.

The single unit of three volcanic horizons of Whittard – the Stapeley Volcanic Member (bounded to the west by shales), the Stapeley Shale Member and, to the east, the overlying Hope Shales – was re-mapped by BGS as a complex of volcanic tuffs and lavas: the Stapeley Volcanic Formation, lying within the Hope Shales.

The disused quarry, centred on SO 3102 9816, presents a 30 m wide and 6 m high face of massive bedded tuffs with strong jointing and areas of spherical weathering. Low down in the centre of the face a fresh cored area shows a grey coarse lithic tuff. Elsewhere are finer tuffs and high up on the left is a small intrusion of chilled very fine grained dolerite.

The volcanoes released a lot of ash and this accumulated as beds within the sedimentary sequence, known as Tuffs. Some ash would fall through the air and then settle into water, becoming quite well sorted and forming thinly bedded sediment. However, if the ash fell onto dry land then it would not get sorted and instead form thickly bedded sediment, as shown here for this tuff from the Stapeley Volcanic Formation:

Tuff from the Stapeley Volcanic Formation
Click image to enlarge
© photograph by Ian Stimpson, Hypocentre

The point SO 3094 9816 marks the SW end of an emergent outcrop of volcanic tuffs which forms a continuous rib running along the NE strike for 200 m and dipping NW 55° to 65°. This is here considered to be a significant geomorphological feature since it demonstrates one of the forms which can result from the erosion of dipping rocks and bears immediate comparison with Hagley Upper Ridge and Cwm Dingle.

A tor-like feature at SO 3100 9825 shows what would appear to be volcanic “bombs” but in fact are larger partially rounded clasts of rhyolitic rock.

The NE end of the continuous rib is at SO 3104 9833 but scattered outcrops continue ahead for some distance.

Off to the left (NW) the ground falls away into a parallel running smooth sided valley. Across on the opposite side can be seen a shale exposure where excavation has yielded abundant dark grey fissile shale fragments representing interbedding of the Hope Shales.

Continuing along the main ridge the ground becomes flatter and outcrops less frequent. At a crossbank a cairn can be seen ahead apparently offset from the trend of the ridge. This cairn at SO 3124 9896 marks the near edge of a large area of dolerite which has totally blanketed the previous landscape of ridge and hollow forming instead a roughly level plateau.

Return to the quarry can be usefully made along the upper parts of the SW slopes where further outcrops of the Stapeley Volcanics occur. It is evidence of the stratigraphic complexity that what was considered by Whittard to be a single unit of three volcanic horizons – the Stapeley Volcanic Member, bounded to the west by shales – the Stapeley Shale Member, and to the east by the overlying Hope Shales (Whittard & Dean, 1979) was re-mapped by BGS as a complex of volcanic tuffs and lavas – the Stapeley Volcanic Formation – lying within the Hope Shales.