Cox, B.M. & Sumbler, M.G. 2002. British Middle Jurassic Stratigraphy. Geological Conservation Review Series, No. 26, JNCC, Peterborough, ISBN 1 86107 479 4.
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M.G. Sumbler
The quarry at Swift's Hill is sited about 3 km north-east of Stroud, Gloucestershire, at the northern side of Swift's Hill SSSI. It exposes much of the middle part of the Inferior Oolite Group, and has a special place in the history of Cotswold geology because Edwin Witchell
The following section is based on that recorded by Buckman (1895) with revised lithostratigraphy by the present author.
| Thickness (m) | |
| Salperton Limestone Formation | |
| Upper Trigonia Grit Member | |
| 1: Limestone, 'ragstone'; 'Terebratula' globata of authors (non J. de C. Sowerby), Rhactorhynchia subtetrahedra (Davidson), Trigonia | c. 1.52 |
| Aston Limestone Formation | |
| Gryphite Grit Member | |
| 2: Limestone, 'ragstone', bluish-grey, much stained with iron, vertical borings | 0.05–0.18 |
| 3: Limestone, 'ragstone', grey, sparsely shelly | 0.28 |
| 4: Limestone, 'ragstone', grey, hard, sandy, some shelly beds; Gryphaea in partings, more common in lower part | 2.13 |
| 5: Sandy 'ragstone', mostly very shelly; with numerous small bivalves in some parts; base very uneven | 1.52 |
| 6: Fine-grained yellow sand | 0.10–0.15 |
| 7: Mudstone, purplish-grey, sandy, with numerous broken shells; scarce | |
| Lobothyris buckmani (Davidson) | 0.08–0.15 |
| 8: Limestone, 'ragstone', grey, shelly, bored in places; Acanthothiris at top | 0.46 |
| Lower Trigonia Grit Member | |
| 9: Limestone, 'ragstone', yellowish, somewhat 'iron-shot', shelly with a few bivalves; highly bored in places; Rhynchonella' bajinensis Szajnocha | 1.52 |
| 10: Marl, yellowish | 0.08 |
| Birdlip Limestone Formation | |
| Scottsquar Member | |
| 11: Ooidal debris | 0.13 |
| 12: Limestone, white, ooidal | 0.96 |
| 13: Marl, brown | 0.03 |
| 14: Marl, grey; Globirhynchia tatei (Davidson), scarce Plectothyris fimbria (J. Sowerby), Trigonia | 0.23 |
| 15: Marl, yellow | 0.03 |
| 16: Limestone, white shelly, ooidal |
At the time of writing (1997), only the upper part of the succession (beds 1 to 9) was exposed in continuous section. The strata are somewhat disrupted by minor faults, probably a result of cambering on the steep hillside, but there is little difficulty in recognizing the units described by Buckman (1895); the sand and marl of beds 6 and 7 form a particularly obvious marker. Lower strata are largely concealed by rubble, although at the southern end of the site there is a small exposure of cream-buff, peloidal wackestone with Plectothyris, belonging to the Scottsquar Member of the Birdlip Limestone Formation (Lower Inferior Oolite), as mentioned by Baker (1981).
Swift's Hill is sited in the axial region of the so-called Painswick Syncline (Buckman, 1901) in which a largely complete succession of the Bird-lip Limestone Formation (Lower Inferior Oolite) and the Aston Limestone Formation (Middle Inferior Oolite) is preserved. The Birdlip Limestone Formation is presently not well exposed at Swift's Hill; it is, however, better exposed at Frith Quarry (see GCR site report, this volume), only 2 km to the north-west. Together with Haresfield Hill (see GCR report, this voume), these quarries form the basis of the generalized section for the Painswick area given by Parsons (1980a).
The Aston Limestone Formation (Middle Inferior Oolite) is 6.35 m thick at Swift's Hill, whereas on the axis of the 'Birdlip Anticline' to the north-east (e.g. Knap House Quarry, see GCR site report, this volume) and south-west (e.g. Leigh's Quarry, see GCR site report, this volume), it is entirely absent. It is, however, much thinner than in the Cleeve Hill area, its area of maximum development, where it reaches some 22 m in thickness (Barron et al., 1997). This relative thinness is due principally to the absence of the uppermost part of the Cleeve Hill succession (see Rolling Bank Quarry GCR site report, this volume), beneath the unconformable base of the Salperton Limestone Formation (Upper Inferior Oolite). Only the Lower Trigonia Grit and Gryphite Grit members are present at Swift's Hill.
The Lower Trigonia Grit Member comprises 'iron-shot' limestones and marls as at Frith Quarry (see GCR site report, this volume) where it has yielded an extensive fauna of (Lower Bajocian) Discites Zone ammonites. The basal marl, not now exposed, includes pebbles of a whitish limestone (Buckman, 1895; Richardson, 1904) presumably derived from the underlying Scottsquar Member. The top of the succeeding Gryphite Grit Member (total thickness c. 4.75 m) is marked by a well-developed hard-ground with borings and abundant encrusting oysters. Buckman (1895) classified the topmost bored beds (2 and 3) as Notgrove Freestone (= Notgrove Member) because of the presence of borings, but the 'ragstone' lithology is typical of the Gryphite Grit Member. The Notgrove Member, in its typical oolite facies is, however, present farther to the north-west in the 'Painswick Syncline', for example at Kimsbury Castle
Only the lower part of the succeeding Salperton Limestone Formation is exposed at Swift's Hill. The strata comprise ooidal packstones, with lenses of richly fossiliferous rubbly limestone, belonging to the Upper Trigonia Grit Member.
Swift's Hill exposes the whole of the Aston Limestone Formation (Middle Inferior Oolite) together with the basal part of the succeeding Salperton Limestone Formation (Upper Inferior Oolite). In combination with other GCR sites, it provides a representative section of the Inferior Oolite Group within the so-called 'Painswick Syncline'.