The stones at Stanton Drew

There are three main circles in the Stanton Drew complex, the Great Circles, the northeast and the southwest circles. In addition there is The Cove consisting of three stones and also a single standing stone known as Hautville's Quoit. The Great Circle is indeed circular, unlike many British monuments of this type and is one of the largest in the country, second only to the circle at Avebury (Burl, 1976). The cove is one of only three others in the country and is thought to be an entrance to an ancient burial chamber (Burl, 1976). There are other monuments and stones associated with this complex (Sibree, 1927) but these have not been included in this study as they are not regularly included in literature about the site.

Placement of the stones at the site

There are many different theories relating to the small scale placement of the Stone Circles. Most agree that the positioning is linked to the calendar and to the orbit and movements of celestial bodies (Sibree, 1919, 1927), (Grinsell, 1956). Indeed, these hypotheses are the major argument for all the stones being placed at the site at the same time.

However, since the magnetometer study at the site in 1997 it has been postulated that the stones were part of a large building (English Heritage).

This may preclude the positioning of the stone as some kind of calendar but does not rule is out completely especially as the magnetometer work did not include the south west circle. This circle in particular is believed to have originally consisted of 12 stones, which are thought to be representative of a twelve month Juliaus calendar year (Sibree, 1919, Grinsell, 1956). In contrast, work from the nineteenth and early twentieth centuries date the complex as Saxon, built in accordance with Roman design (Sibree, 1927).

Transport of the stones

The transportation of large rocks from their provenance area to the site was no small undertaking in the Stone Age. It is well documented that the great stones that make Stonehenge on Salisbury Plain were moved over 200 miles from South Wales, around or across the Severn estuary to their present location. T has been postulated that the stones at Stonehenge, may have been moved closer to the southerly site by Wolstonian ice sheets in the last ice age. This idea is also applied to the stones at Stanton Drew. The area of the circles might have been a moraines at the end of Chew Gorge (Kellaway, 1971).

Some of the stones at Stanton Drew weigh up to 27 tonnes (Kellaway, 1971). They appear to be made of local lithologies and it is a more accurate provenance of these lithologies that this project is trying to determine. All the possible lithologies would be available within approximately an eight mile radius of the Stanton drew site. Other modes of transport for stones used in circles have been offered, and include boat and river transport. The River Chew runs roughly northwards from the Mendips via Chew Valley Lake to the Avon. It may have been utilised in transporting the stones as the river and the lake are both positioned in favourable locations in relation to Stanton Drew and the Mendips.

Geology of the Mendip Hills

In Triassic times the area that is now the Mendip Hills was a mountainous region, the high relief being formed by the Silurian-Carboniferous basement. The Mercia Mudstone was deposited in an inland playa type environment between the mountains. It is compromised of red beds of mud and siltstones with grey-green reduced horizons. It reaches up to 460 metres thickness in places and is found extensively throughout the Chew Valley. It is on this lithology that the village of Stanton Drew stands.

The Butcombe Sandstone is interbedded with the Mercia Mudstone and outcrops frequently throughout the valley and is generally thought to represent physical phases.

The Carboniferous Limestone hills are edged by alluvial fans deposited at the time of the Variscan Orogeny as the Dolomitic Conglomerate formation. These fans are mainly matrix supported conglomerate deposited by debris flows. The fans represent the detritus derived during the final phases of the erosion of the Amorican mountains (Green and Welch. 1965). The majority of the standing stones at Stanton Drew are made of Dolomitic Conglomerate, and most of these have undergone some degree of diagenetic silicification.

The nearest Triassic alluvial fan to Stanton Drew is at Winford five miles to the west. This fan is not known to be silicified unlike the fan near East Harptree and Compton Martin on the eastern side of Blackdown, about five and a half miles south west of Stanton Drew (see fig 4). The Dolomitic Conglomerate lies unconformably here on the folded Carboniferous basement. The Carboniferous strata here include the Burrington Oolite and the Cheddar Limestone formations. The Old Red Sandstone of the Devonian forms the core of the Mendip Hills and is responsible for the distinctive red colouring of the soils in the area. The Triassic is in fact much redder that the Devonian strata of the area, probably due to diagenetic and post diagenetic processes.

The alluvial fan at Harptree is faulted and has been extensively mined for lead and zinc deposits. This indicates it may have been hydrothermally altered in some way, which could be responsible for the alteration to a silicified conglomerate.

There are some andesites in the region, but none have been found in close proximity to the silicified fan. Any veins are very localised and restricted in the eastern end of the fan and do not appear to extend into the Triassic strata. There is some dip-slip faulting in the same area which does cut some of the Triassic material.

The Mendip Hills Orefield

The orefield in the Mendip Hills is found in the Carboniferous Limestone and the Dolomitic Conglomerate. Lead and zinc are the most economically important and abundant elements. Galena (lead-sulphide) and smithsonite, also known as Calamine (zinc carbonate) are the main minerals. Calamine was particularly abundant in the Dolomitic Conglomerate surrounding East Harptree (Woodward, 1876). The minerals tend to exist in veins and fissures and are associated with a gangue of calcite and sometimes baryte.

Iron Ores are also found in the district and are largely disseminated into the Dolomitic Conglomerate. Iron Ores include hematite and Limonite but were much less abundant than the lead-zinc mineralisation. It is possible the iron emplacment predated the lead zinc episode in some areas as the iron ores can be seen to line the veins of lead and zinc deposits.

Lead isotope abundances gave a mean age of the mineralisation at 230 +/-30Ma. This would place the mineralisation in the late Permian-early Triassic (Moorbath, 1962). Therefore the mineralisation of the Mendips came after that of the Cornwall-Devon area. The latest beds to be directly affected by the mineralisation are the upper Mercia Mudstone succession.

The silicification of parts of the Dolomitic Conglomerate is post lead-zinc mineralisation age. The Biddle fault (see fig 4.) is proposed as pre Albian in age. The alteration is apparently more concentrated on either side of the fault as this suggests the fault was in place at the time of the silicification (Green, 1965). Green and Welch (1965) suggest the alteration is due to metasomatic replacement and is hydrothermal in origin. They support this claim with the appearance of small amounts of Galena and sphalerite in the altered beds and suggest this is related to a later episode of mineralisation and is post-Albian in age (Lower Cretaceous).

East and West Harptree have been the centre of much mining. Earliest mining of the Mendips took place at least 49AD, six years after the Romans entered Britain though it may have taken place over 200 years before (Gough, 1930). The mining activity peaked in the 17th century and continued into the early part of this century.