Field Meeting in the Forest of Dean10-12 June 1966

Report by the Director: J. G. CAPEWELL

Received 18 November 1966

Friday, 10 June

TWENTY-SEVEN MEMBERS of the Association assembled at Littledean House,Littledean, Gloucestershire, for the meeting. After dinner, the Directorgave a short talk on the geology of the Forest of Dean and adjacent areasand outlined the programme for the week-end. The object of the excursionwas to present as broad a view as possible, within the available time, of thesuccession, structure and geomorphology of the area, and this wouldnecessitate going outside the strict limits of the Forest of Dean.

Saturday,l1 June

On a misty morning the party travelled by coach via Cinderford andNailbridge to Plump Hill, the geological features being pointed out enroute. From a suitable vantage point (SO 663173) above The Point, theDirector demonstrated as far as was possible the general features of theeastern flank of the Dean syncline. Closer at hand, the Director was ableto show the position of the mappable boundary between Devonian and theCarboniferous, where the yellowish sandstones at the top of the TinternSandstone Group are succeeded abruptly by the first limestones of theLower Limestone Shales. The latter formation was then studied in theeasternmost of the series of quarries along the northern side of the mainroad at Plump Hill. The overturning of the dip of one of the limestonebands was noted and its origin discussed.

The party then moved into the large quarry in Lower Dolomite, theunbedded nature of most of which provoked discussion. The Directorsuggested that this rock may have originally been a reef limestone, sincedolomitisation did not normally obliterate the bedding. The quarryexposes virtually the full thickness of the Lower Dolomite; its steep dipbecomes apparent in the uppermost beds.

The Crease Limestone, a coarse crystalline dolomite and the principalhaematitised horizon, was then seen in a series of old excavations runningnorthward along the strike from a point on the main road immediatelywest of the chapel (SO 661171). From here the party moved across to thequarry, now virtually infilled, 200 yards north-north-west of the chapel, inthe Whitehead Limestone. Enough rock is exposed in situ, however, todemonstrate the algal nature of this limestone.

The party then walked through the plantation northward for about half

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208 J. G. CAPEWELL

a mile, noting small exposures of the Drybrook Sandstone, and thenturned north-westward across the Wigpool syncline to Puddlebrook.Some time was spent here in the quarry (SO 656183), occasionally workedfor building- and brick-facing sand, in Drybrook Sandstone. Its un­expected, deltaic, facies and its palaeogeographical significance provokeddiscussion. From the conspicuous shale band in the quarry, plant-remains,including sporophylls of Lepidostrobophyllum (Allen, 1961),were collected.

After lunch at a nearby inn, the Director demonstrated the positionsof the outcrops on the western flank of the Wigpool syncline, the party thenmoving on into the road-cutting north-east of Euroclydon (SO 643187).This displays a fine section in the Tintern Sandstone Group, consistinglargelyof greenishhighly micaceouscurrent-bedded sandstones (for detailedsuccession see Welch & Trotter, 1961,51). At the corner at the northernend of the cutting, the topographical features of the Hope Mansel hemi­dome, the complementary structure to the Wigpool syncline, were demons­trated. At Bailey Gate, about 300 yards down the hill, road-side crags ofthe Quartz Conglomerate were examined. At this point the Director madereference to unpublished work on the sedimentology of the Upper OldRed Sandstone by Mr. A. J. Halliwell, who, from a study of the petro­graphy, had been led to infer a northerly or north-westerly provenance forthe sediments, from a region of Pre-Cambrian rocks.

The party then went by coach via Lea to Longhope railway station,thence walking up the lane to the well-known Hobbs Quarry in the Wen­lock Limestone (SO 695190), thence across the fields towards the railwaybridge. On the way the oolitic and partly dolomitised development of theupper part ofthe Wenlock Limestone wasseen in an old quarry (SO 694189).In the sunken lane farther down, the fossiliferous, calcareous siltstones ofthe Ludlow Series were seen; reference was made to the detailed work ofLawson (1955)on these beds and his conclusions summarised.

From Longhope station the party returned to headquarters by way of theWilderness Quarry (SO 672185), which exposes a fine section showingtypical rocks of the Brownstones division of the Lower Old Red Sandstone.

Sunday, 12 June

The party went by coach to the Strand at Westbury-on-Severn andwalked along the foreshore to the section of Keuper and Rhaetic beds atGarden Cliff (SO 718128).The detailed succession was studied with the aidof the diagram compiled by L. Richardson and published on the occasionof the Gloucester meeting in 1934 (Gardiner and others, 1934, 134). Thepalaeontological and sedimentological features of the Rhaetic arousedgreat interest.

Having returned to the coach, the party then travelled via Newnhamand Blakeney to Severn Bridge station. In a heavy downpour, the party

FIELD MEETING IN THE FOREST OF DEAN 209

made its way through Purton and under the railway to the Severn foreshore,where the deposition at high water of estuarine silts was noted and theresult experienced. In the cliff and shore section, the Raglan Marls of theOld Red Sandstone were compared and contrasted with the Keuper Marls,seen at the previous stop. The greater tectonic deformation of the RaglanMarls was the most obvious feature, and at one point (SO 671044), asteeply dipping reverse fault, with marked drag on the upthrow side, is wellexposed. The presence of strong bands of current-bedded sandstones, andof nodular cornstones, the origin of which caused some discussion, wereother features noted. The party moved on along the shore, pausing to notethe use of local Pennant Sandstone in the construction of the landwardpiers of the now disused Severn Railway Bridge, before returning to thecoach by field-path.

A rapid traverse by coach across the Forest of Dean was then made byway of Blakeney, Parkend, Cannop and Berry Hill to the Rock Inn, nearSymond's Vat, features of interest being pointed out en route. After lunchthe party went on as far as the new coach-park at Symond's Vat. Theearthworks shown on the 2t-in. Ordnance Survey map as Offa's Dyke werebriefly inspected and the party moved on to the wooden foot-bridge, andexamined an excellent exposure of the Crease Limestone, here a coarsecrystalline dolomite. A hundred yards down the hill a problematic featurein the Lower Dolomite, probably an infilled collapse structure, was studied.A return was then made to the summit of Symond's Vat Rock (SO 564160),also composed of Lower Dolomite; here the view and its geomorphologicalimplications were much admired.

On the return journey to headquarters, a final halt was made at someroad-side quarries near Miry Stock (SO 617148), where typical PennantSandstone is well exposed. A search for plant fossils in a shale lens wasunsuccessful.

At this point, appreciative votes of thanks to the Director and tothe Secretary (Mr. F. E. Jarvis) were proposed by the Rev. F. M. HodgessRoper. The party reached Littledean at 4 p.m. and dispersed.

REFERENCESALLEN, K. c. 1961. Lepidostrobophyllum fimbriatum (Kidston, 1883) fromthe Drybrook

Sandstone (Lower Carboniferous). Geol. Mag., 98, 225-9.GARDINER, C. I.. G. A. KELLAWAY, S. H. REYNOLDS, STANLEY SMITH & A. E.TRUEMAN.

1934. The Geology of the Gloucester District. Proc. Geol. Ass., 45, 109-44.LAWSON, J. D. 1955. The Geology of the May Hill Inlier. Q. JI geol. Soc. Lond., 111,

85-116.WELCH, F. B. A. & F. M. TROTTER. 1961. Geology of the Countryaround Monmouth

and Chepstow. Mem, geol, Surv, U.K.

Department of Civil EngineeringThe City University51. John Street, London E.C.I

PROC. GEOL. ASS., VOL. 79. PART 2,1968 14