<<

used as a high quality building stone. Towards the top of the the North - a become more fossiliferous and are widely referred to as ‘grits’ due to their coarser Geological outline texture. Judy Hible Lying above the Inferior Oolite is the . This consists of an To the north-west of Wiltshire, the extremely varied sequence of rocks that can rocks crop out in succession, dipping south- change quite dramatically both through the eastwards under the . From young to sequence and geographically across the area. old these Jurassic rocks are: Important formations within the Great Oolite include the Fuller’s Earth, a thick bed of clay Inferior Oolite and Upper Lias; that contains a which was used to Great Oolite Group (includes Fuller’s Earth); remove grease from fleeces and contributed Clay and Sand; greatly to the success of the Cotswold wool Corallian Beds; trade in the Middle Ages. Other formations ; important to the area’s economy today are the Wealden, Purbeck and Portland Beds (not White , quarried as an aggregate, seen locally). the Chipping Norton Limestone, quarried as an aggregate and a building stone, and the Above these are rocks which can Eyford Member, used to produce traditional be seen on the highest ground including Cotswold roofing 'slates'. Lower ; Clay; The Quaternary deposits of the Upper Greensand. (Table 1) comprise varied unconsolidated beds, referred to collectively as "Drift". These include glacial, Table 2 shows the local outcrops. fluvial and a mixed group of periglacial deposits known as "Head". These are In this area of Avon Vale these outcrops trend scattered widely across the area but their from SW to NE heaviest concentrations occur in the Vale of Moreton and in the area around , The following is a brief description of each where they are extensively worked for their area, its associated bedrock and the setting in gravels. which the rocks were formed.

Fossils: Area: Bedrock Terebratula bullata in the Fullers Earth, ‘lamp shell’, , Great Oolite Morgan’s Hill, Down: Lewes Nodular Chalk Formation, Seaford Chalk Formation And Newhaven Chalk Formation (undifferentiated). Sedimentary Bedrock formed approximately 71 to 94 million years ago in the Cretaceous Period. Local environment previously dominated by warm chalk seas.

Setting (1): warm chalk seas. These rocks were formed in warm shallow 'Chalk' shelf seas with little sediment input from land. They often consist of a ooze of the microscopic remains of plankton, especially the disc- shaped calcite plates or that make up the spherical .

Others include , bivalves, : West Melbury Marly ammonites, , sea-urchins. Chalk Formation And Zig Zag Chalk

Journal of the Bath Geological Society, No. 34, 2015 9

1:625 000 1: 50 000

Cretaceo Grey chalk subgroup West Melbury Marly Chalk us Formation

Zig Zag Chalk Formation

White chalk subgroup

Selborne Group Gault Formation Gault Formation Upper Greensand Upper Greensand Group Formation

Lower Greensand Lower Greensand Group Group

Jurassic Corallian Group Hazelbury Bryan Formation

Ancholme Group Formation Ampthill Clay Formation Kimmeridge Clay Formation Kimmeridge Clay Red Down Sand Formation Formation

Kellaways Formation Kellaways Clay Member Formation Kellaways Sand Member Oxford Clay Formation

Great Oolite Group Chalfield Oolite Formation Combe Down Oolite Member Limestone Formation

Table: 1 : Succession in North Wiltshire fragments or clasts of silicate ) Formation (undifferentiated) - Chalk. deposited as mud, silt, sand and gravel. Sedimentary Bedrock formed approximately 94 to 100 million years ago in the Cretaceous Stockley, Blackland, : Gault Period. Local environment previously Formation - Mudstone. Sedimentary Bedrock dominated by warm chalk seas. formed approximately 100 to 112 million years ago in the Cretaceous Period. Local Setting: as Setting (1) environment previously dominated by shallow seas. , , Cherhill: Upper Greensand Formation - Calcareous Setting: As Setting (2) And Siltstone. Sedimentary Bedrock formed approximately 94 to 112 Sandy Lane, Mile End Hill: Lower Greensand million years ago in the Cretaceous Period. Group - Sandstone. Sedimentary Bedrock Local environment previously dominated by formed approximately 100 to 125 million shallow seas. years ago in the Cretaceous Period. Local environment previously dominated by shallow Setting (2): shallow seas. These rocks seas. were formed in shallow seas with mainly siliciclastic sediments (comprising of Setting: As Setting (2)

Journal of the Bath Geological Society, No. 34, 2015 10

White Chalk Subgroup Lewes Nodular Chalk Formation - Seaford Chalk Formation Newhaven Chalk Formation

Holywell Nodular Chalk Formation - Turonian New Pit Chalk Formation

Grey Chalk Subgroup West Melbury Marly Chalk Cenomanian Formation Zig Zag Chalk Formation

Selborne Group Gault Formation

Upper Greensand Formation Albian - Cenomanian

Lower Greensand Lower Greensand Group Aptian - Albian Group

Ancholme Group Ampthill Clay Formation - Kimmeridge Clay Formation

Corallian Group Hazelbury Bryan Formation Oxfordian

Kingston Formation - Limestone Oxfordian

Kingston Formation - Mudstone Oxfordian

Ampthill Clay Red Down Sand Formation Oxfordian Formation

Ancholme Group - Oxfordian Oxford Clay Formation

Corallian Group Oxfordian

Ancholme Group Kellaways Formation Callovian

Kellaways Formation Kellaways Clay Member Callovian

Ancholme Group Kellaways Formation Callovian - Oxfordian Oxford Clay Formation

Kellaways Formation Kellaways Sand Member Callovian

Ancholme Group Oxford Clay Formation Callovian - Oxfordian

Great Oolite Group Cornbrash Formation - Callovian

Forest Marble Formation Bathonian

Table 2: Local Outcrops

Journal of the Bath Geological Society, No. 34, 2015 11

Quemerford:, Whetham, Mile End: Ampthill Setting: As Setting (2) Clay Formation And Kimmeridge Clay Formation (undifferentiated) - Mudstone. Bumpers Farm, Allington, Easton, Sedimentary Bedrock formed approximately Hungerdown: Cornbrash Formation - 151 to 161 million years ago in the Jurassic Limestone. Sedimentary Bedrock formed Period. Local environment previously approximately 161 to 168 million years ago in dominated by shallow seas. the Jurassic Period. Local environment previously dominated by shallow carbonate Setting: As Setting (2) seas.

Calne: Stanford Formation - Limestone. Setting: As Setting (3) Sedimentary Bedrock formed approximately 156 to 161 million years ago in the Jurassic Yatton Keynell, West Yatton: Forest Marble Period. Local environment previously Formation - Mudstone. Sedimentary Bedrock dominated by shallow carbonate seas. formed approximately 165 to 168 million years ago in the Jurassic Period. Local environment Setting (3): shallow carbonate seas. These previously dominated by shallow seas. rocks were formed in warm shallow seas with carbonate deposited on platform, shelf and Setting: As Setting (2) slope areas; often rich in corals and shelly faunas. May include evaporites where Ford: - Limestone. seawater was trapped and salts concentrated Sedimentary Bedrock formed approximately by evaporation. 165 to 168 million years ago in the Jurassic Period. Local environment previously , Studley, Derry Hill: Hazelbury Bryan dominated by shallow carbonate seas. Formation - Sandstone. Sedimentary Bedrock Setting: As Setting (3) formed approximately 156 to 161 million years ago in the Jurassic Period. Local environment previously dominated by shallow seas.

Setting: As Setting (2)

Stanley, Tytherton, Ratford, Pewsham: Kellaways Formation And Oxford Clay BREMHILL Formation (undifferentiated) - Mudstone. Sedimentary Bedrock formed approximately 156 to 165 million years ago in the Jurassic Judy Hible Period. Local environment previously dominated by shallow seas. The parish of Bremhill contains a collection of smaller parishes in valleys with Bremhill Setting: As Setting (2) prominent on a hill. The smaller hamlets are Tytherton Lucas, East Tytherton, Foxham, Langley Burrell, Lowden: Kellaways Sand Charlcutt, Spirthill, Stanley and Bremhill Wick. Member - Sandstone. Sedimentary Bedrock It is in the Diocese of , Archdeaconry formed approximately 161 to 165 million years of Wiltshire and the rural deanery of . ago in the Jurassic Period. Local environment The village lies two miles north west from previously dominated by shallow seas. and four from .

Setting: As Setting (2) Bremhill is located on Wick Hill, a corallian which falls sharply to the valley of Hill Corner, Hardenhuish Lane: Kellaways the river Avon. The geology is from the upper Clay Member - Mudstone. Sedimentary oolite, providing loam, brash and clay soil. Bedrock formed approximately 161 to 165 The Wiltshire and Canal ran through million years ago in the Jurassic Period. Local the centre of the parish from the north east to environment previously dominated by shallow the south west. seas.

Journal of the Bath Geological Society, No. 34, 2015 12