West, Ian M. 2015. Mendip Hills - Geological field guide. Supplement to Geology of the Wessex Coast. Internet site: www.southampton.ac.uk/~imw/Mendip-Hills.htm. By Ian West, Romsey, and School of Ocean and Earth Science, Southampton University. Version: 31st August 2015. [2458 lines]

Ian West,

Romsey, Hampshire

and:
Faculty of Natural and Environmental Sciences,
Southampton University,

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Cheddar Gorge, Mendip Hills, Somerset, introductory view down the gorge, just up from The Horseshoe, 29th July 2015

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LOCATION - GENERAL

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INTRODUCTION:

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INTRODUCTION

Geological Maps

For the eastern Mendips, see the British Geological Survey, Wells Sheet, No. 280, Solid and Drift and the the Frome Sheet, No. 281, Solid and Drift, 1:50,000 of the British Geological Survey. These maps can be purchased from the BGS bookshop, online.

Example part of the BGS Geological Map, 1:25,000, Sheet 45, and which includes Cheddar Gorge, Mendip Hills, Somerset

A special Geological Sheet ST 45 Cheddar, scale 1:25,000 covers the Cheddar area in detail. This map really should be obtained by anyone interested in the geology of this area. It is very clear and easy to read and it explains the Cheddar area in its structural perspective.

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Cheddar Gorge Geology - Maps with Local Detail

A simplified geological of Cheddar Gorge, Mendip Hills, Somerset, with some topographic detail, by Ian West, version 20Aug15

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A modified and partially redrawn, geological map of Cheddar Gorge, Mendip Hills, Somerset, based on the version in Green and Welch, 1965

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A map showing local detail of parts of Cheddar Gorge, Mendip Hills, Somerset

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INTRODUCTION continued:

Safety

Many of the exposures in this area are in quarries, either working or abandoned. Please abide strictly by the rules of working quarries. In abandoned quarries take care not approach from above unstable cliff edges. From beneath take care with regard to risk of falling rock. Do not hammer chert, which occurs in the Carboniferous Limestone, and which, when struck, can give off very dangerous splinters that can cause loss of eye sight. Take the usual precautions of using sturdy footware and take suitable clothing when walking on upland areas. Be particularly careful with the steep walls of Cheddar Gorge. Do not climb these, and do not ascend other than by using proper footpaths. Take car on irregular and/or slippery rocks in and around Cheddar Gorge and other localities. Beware of the risk of occasional falling rocks in the gorge. Do not enter caves, other than commercially operated ones, and do not undertake caving without proper equipment and without the assistance of experienced people and knowledge of the cave systems. When making geological studies in Cheddar Gorge, Burrington Coombe or other places, take care not to ignore road traffic. This can be a significant risk, particularly to parties walking on the roads. Note that there is no roadside pavement in Cheddar Gorge, there are many bends and vehicles, particularly cars can pass close by and at some speed. It is easy to be involved in geological study or geological photography and to accidently walk backwards onto the busy and rather narrow road. Be careful on irregular or loose blocks, as in Landslip Quarry, Cheddar Gorge and other places. In the coastal extension of the Mendip Hills in the Weston-super-Mare area, there are risks from rising tide and from walking into soft mud at low tide. This webpage is purely descriptive and it does not recommend that any particular activity takes place. It is not an itinerary. You do not have to go anywhere and if you go, you go at your own risk.

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CHEDDAR GORGE (new section in progress)

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Cheddar Gorge Geology - Introduction

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The thickness of the Carboniferous Limestone in the Mendip area and in relation to South Wales by George (1972), fig. 1. The thickness is very great in the Mendips, being between 900m in the northwestern part and increaseing to 1100m in the southeastern part of the range of hills. At Cheddar Gorge the thickness is about 1 kilometre. Compared to other areas, this great thickness is similar to that in the Gower Peninsula, South Wales. The thickness is less to the north, and is soon zero, as St. George's Land is approached (i.e. now central Wales). The increase in thickness towards the south is greatest at Bosherton in the Pembrokeshire area, where the Lower Carboniferous or Dinantian (Avonian in old terminology) reaches almost 1500 metres. Thus the Mendip sequence is a very thick carbonate facies. It is also near the southern limit of the limestone facies. Further to the south, in Devon, the non-carbonate Culm facies occurs.

The Carboniferous Limestone of the Mendips is of shelf facies. It has several oolite horizons which are clear indicators of high-energy, clear shallow water. Fossil coral remains are common, again indicating shallow, marine water. So, it is a major and very thick, carbonate shelf facies, showing only minor oscillations in depth and of specific type of carbonate rock. It is quite surprising that carbonate shelf facies could be maintained in fairly uniform conditions for such a long interval of time.

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Lion Rock of Clifton Down Limestone and at the entrance to Cheddar Gorge, Mendip Hills, Somerset, 6th August 2015

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Rectilinear jointing and bedding are structures controlling the topography of the cliffs of Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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From near Gough's Cave, looking up Cheddar Gorge, Mendip Hills, Somerset, in stormy conditions, with approaching rain

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A Southampton University student field trip to Cheddar Gorge, Mendip Hills, Somerset, in April 1998

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A composite image for location purposes, the bus turning area, up Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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Cheddar Gorge Geology - The Clifton Down Limestone Formation

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[N.B. These are only introductory notes.]

The part of the Carboniferous Limestone Group into which Cheddar Gorge is cut is the Clifton Down Limestone Formation. See the BGS Lexicon of Named Rock Units (just Google - "Clifton Down Limestone Formation"). This is from a higher part of the Carboniferous Limestone Group. It is Arundian to Holkerian in age [about middle Visean, about 340 million years old, in simple terms].

Its main characteristics can be summarised as follows:
This formation consists of splintery dark grey calcite and dolomite mudstones, pale grey oolitic, dark grey bioclastic and oncolitic limestones and some mudstones (after BGS). Scattered cherts and silicified fossils occur within part of it. In Cheddar Gorge it is not easy to see the details because of dark joint surface, which rarely shows much detail. A favourable exposure with good weathering is needed.

The Clifton Down Limestone Formation is 266m. in the Avon Gorge but thins to 150 to 200m in the Mendips (BGS Lexicon).

This is carbonate sediment from shallow water in a hot, nearly equatorial environment. Cheddar Gorge area was just south of the equator at the time. The sea was shallow and clear and suitable for the growth of corals. The limestone was deposited in a variety of settings, from shallow carbonate shelf to barrier or back barrier (or even lagoon).

The fauna of the Clifton Down Limestone is marked by an abundance of individuals in places. In Cheddar Gorge a rich fauna will not easily be found because of the type of exposure, as mentioned above. In reality there is an abundance of individuals but a paucity of species (Green and Welch, 1965). It includes the coral Lithostrotion martini (this has groups of corals which are circular in cross-section). Basaltiform (i.e hexagonal) Lithostrotion corals also occur. In practice, in the field the species cannot be identified but lithostrotion is quite easily found, particularly at Landslip Quarry. Composita ficoidea ["Seminula ficoidea" in old literature] is a smooth-shelled brachiopod that is apparently common, but not easy to see. A large productid brachiopod Productus corrugatohemisphericus has been found in this limestone, although not necessarily in Cheddar Gorge. In summary, you are most likely to see colonies of Lithostrotion, usually of a non-basaltiform type. Some photographs of rather poor specimens are shown in this webpage.

Some obvious palaeoenvironmental conclusions can be drawn from the Lithostrotion corals. Water salinity could not have exceeded about 50 ppt (parts per thousand). Condition in much of the Arabian Gulf are broadly similar today, but close inshore to UAE the salinity rises above 50 and it is too hypersaline to compare to this Carboniferous Limestone of Cheddar Gorge. This is compatible with the rarity of evaporites in the limestone sequence here. Carboniferous Limestone evaporites do occur in the Mendips but are not abundant here (elsewhere Lower Carboniferous evaporites are well-developed; the climate was appropriate for their precipitation, but the environments were not always appropriate.).

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Cheddar Gorge - Relatively Recent Erosion

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A broad view of Cheddar Gorge and the Cheddar Reservoir, Somerset, from the high cliffs above the south side of the gorge

Cheddar Gorge is very youthful, probably almost entirely of Pleistocene origin and it lacks river terraces. Most stream and river valleys in the south of England have had a progressively downcutting development, leaving terraces as indicators of their history. There are usually recent river or stream valleys within older valleys. In the Mendip Hills some of the valley systems are very old. Burrington Coombe, for example, has a precursor of Triassic age, now partly filled with Triassic debris, the Dolomitic Conglomerate. There was a desert wadi there about 250 million years ago. This is not the case in the lower and main part of Cheddar Gorge. As the photograph above shows, there is no trace of a pre-existing valley here.

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Cheddar Gorge Geology - Landslip Quarry

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John Wainwright and Co. were quarrying limestone here, opposite High Rock, in 1902. There was stone crushing machinery and steam drilling machines. In February 1906 a major landslide blocked the gorge here ( Carter, 2014). There is a photograph of the landslide area, apparently matching the eastern part of the quarry, in the book by Pickering and Foster (2011) Cheddar through Time.

The rock fall was was blamed on the quarrying operations. The National Trust at about this time purchased the north side of Cheddar Gorge (the south side belongs to the Longleat Estate). The Trust objected to quarrying operations here and they ceased.

For more information go to: British Geological Survey - History, West Mendip Quarries.

The back boundary fissures of the landslide are vertical to overhanging (particularly overhanging in the case of the lower plane). They are red-stained, suggesting that they were joints (or faults) in existence in Triassic times. Travertine has been been formed much more recently. This has vertical stripes, resulting from downward water seepage. Notice that the blocks of the landslide are much larger than normal quarrying blocks. These angular blocks are at various angles in the eastern part of the old quarry area. Some of them are tilted down towards the road.

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A view obliquely downwards towards Landslip Quarry in Cheddar Gorge, Mendip Hills, Somerset, taken from near High Rock

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A general view of Landslip Quarry, Cheddar Gorge, Mendip Hills, Somerset, 20th July 2015

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At Landslip Quarry, Cheddar Gorge, Mendip Hills, looking across to High Rock, 29th July 2015

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Looking southwest from the Landslip Quarry, Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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Cheddar Gorge Geology

The Pinnacles and the Vertical Jointing Zone.

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The Pinnacles at Cheddar Gorge, Mendip Hills, here viewed upwards, are located on a major zone of jointing which crosses the gorge

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The two Pinnacles of Cheddar Gorge, Mendip Hills, seen from the hilltop above

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Extensional jointing in the Carboniferous Limestone of Cheddar Gorge, Mendip Hills, Somerset, perhaps of Jurassic date

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Extensional fissuring in the Carboniferous strata of the Mendip Hills has been described and discussed by Wall and Jenkyns (2004) [ Wall, and Jenkyns, 2004. The age, origin and tectonic significance of Mesozoic sediment-filled fissures in the Mendip Hills (SW England): implications for extension models and Jurassic sea-level curves.Geol. Mag.]. They reported that in the eastern Mendip Hills, on the northern margin of the Wessex Basin, SW England, the Carboniferous Limestone is cut by numerous fissures that are filled with Mesozoic sediments (sedimentary dykes, neptunian dykes)... The vast majority of the Mendip fissures are interpreted as having formed as a response of the Carboniferous Limestone, north of major basin-bounding faults, to pulses of tectonic extension during Ladinian-Norian/Rhaetian, late Hettangian-early Sinemurian, late Sinemurian-early Pliensbachian, mid-Pliensbachian, late Pliensbachian and Bajocian times.

In Cheddar Gorge, particularly in the area of the Pinnacles and the Horseshoe Bend, there are numerous, well-developed, open joints or fissures. These trend NE to SW. They do not usually show slickensides nor obvious sediment fills, although it does not mean that they are not necessarily present somewhere in the area.

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Cheddar Gorge Geology - Tectonism - Faulting, Slickensides and Brecciation

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The location of the slickenside and downbulge section in a car park, lower Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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A slickensided fault surface and a tectonic downbulge at a car park in the lower Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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A tectonised zone of Clifton Down Limestone, adjacent to strike-slip faults, lower part of Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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Strike-slip faulting in the lower part of Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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A strike-slip fault seen in the vicinity of the Landslip Quarry, but south cliffs, Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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A good and easy place to see the effects of Variscan tectonic activity is a short distance up the Gorge from Gough's Cave (at a small car park on the south side). At first sight two slickensided surfaces can be seen at the eastern end of the car park. Looking up it will soon be noticed that the bedded limestone passess laterally into a cemented limestone breccia. There does not seem to be significant vertical displacement. The brecciation is quite major and thus the tectonic movement was on quite a significant scale. The fault planes does not seem to have been open to Trias because of lack of red material. Obviously, for this region, a dolomitic conglomerate origin must be considered, but the association with strike-slip faulting makes this more likely to be of tectonic origin. Notice that on the large scale geological map of Cheddar Gorge by the British Geological Survey, "disturbed strata" is recorded in the top cliffs, approximately above this area.

(Incidently, beware of busy car traffic at the sharp curve in the road here; it is easy to step back into traffic).

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Cheddar Gorge Geology - Clifton Down Limestone,
(Lower Part is splintery and with chert)

Clifton Down Limestone, the lower splintery part, above the Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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A conspicuous, continous band of chert from near the base of the Clifton Down Limestone, Cheddar Gorge, Mendip Hills, Somerset

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Cheddar Gorge Geology - Clifton Down Limestone,

Fossil Content

Ian West points out the coral Lithostrotion in the Clifton Down Limestone, lower part of Cheddar Gorge, Mendip Hills, Somerset, in April 1998

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The fossil coral Lithostrotion, seen on a bedding plane, Clifton Down Limestone, Landslip Quarry area, Cheddar Gorge, Mendip Hills, Somerset, April 1998

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Fossiliferous, reddish limestone beds in the Clifton Down Limestone, lower part, Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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Fossil corals and brachiopods seen in cross-section in a cliff face of the lower part of the Clifton Down Limestone, Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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Red-stained branching corals, Lithostrotion, Clifton Down Limestone, Landslip Quarry, Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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The branching coral Lithostrotion is abundant in the lower part (with chert) of the Clifton Down Limestone of Cheddar Gorge. It is most easily found in the vicinity of Landslip Quarry. Various photographs of this are shown above.

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A thin bed of bioclastic limestone, probably with brachiopods, Inner cliff of the Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset

A thin bed at about the base of the Clifton Down Limestone Formation, and about 30cm or so in thickness, can be seen to contain abundant fossils at the inner cliff of the Horseshoe Bend, northeastern side. The fossil are not perfectly exposed but seem to be sections through brachiopods. A photograph of a very small part of the rock face is shown above. Much of the bed is obscured by a dark weathering crust and there it does not show the fossil content.

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Cheddar Gorge Geology -

Triassic Red Staining

A vein of red-stained, fibrous calcite in the Clifton Down Limestone, northeast of Gough's Cave, Cheddar Gorge, Mendip Hills, Somerset

It is very common in the Mendip Hills to find patches of reddish limestone, in amongst the generally grey Carboniferous Limestone. This is usually the result of Triassic red sediments, which originally occurred above the Carbonferous strata over much of the Mendip Hills. Veins of red-stained, fibrous calcite can be seen in places, and some photographs are shown above.

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CHEDDAR GORGE - CAVES AND HYDROGEOLOGY

The Stanton Survey and Interpretation

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Hydrogeological interpretation of the Cheddar Gorge, Mendip Hills, Somerset, following a survey by Dr. W.I. Stanton, 1985, section redrawn with minor additions

[notes to be added]

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Cheddar Gorge - Cave Geology -

[newly commenced part of webpage - in progress, first stages!]

Water Input above Horseshoe Bend

A water input location with stratal-related, rectangular caves, above the Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset, 6th August 2015

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Temporary water flow at the road near two rectangular swallet caves, above the Horseshoe Bend, Cheddar Gorge, Mendip Hills, Somerset, 29th July 2015

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Up the gorge, a short distance above Horseshoe Bend, there are two small rectangular caves on the south side of the gorge. They are obviously stratal related and they are associated with clear evidence of water input along widened bedding planes in the limestone (probably Cheddar Oolite Formation). There is little doubt that this is a former input are into the major cave systems of Gough's Cave and Cox's Cave further down the gorge and also on this south side.

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Cheddar Gorge - Cave Geology -

Gough's Cave

Gough's Cave and Cox's Cave are the two showcaves at the southwestern end of Cheddar Gorge. They are the main reason that many people visit the gorge. I have, of course, visited the public parts since youth, and have done a little guided caving (on a safety rope), by arrangement, in Gough's Cave. I have never done any independent caving in Cheddar Gorge. Any details here, other than basic geological information, are from the literature.

[Summary from Barrington and Stanton (1977)]

"Gough's Cave is an abandoned upper level of the Cheddar underground river. Water rose through the Boulder Chamber floor, first forming the Great Oones Hole via King Solomons Temple, then Long Hole via the Fonts, finally emerging to daylight via the present entrance.

The cave, originally a low tunnel extending to a choke just short of the Fonts, was dug open to the public by R.C. Gough and his sons, 1890-1898 and was opened to the public in the latter year. Gough had to wait many years, until the death of an old woman who lived in the entrance passage, before he could start digging. Flints and bones were found during deepening of the entrance passage, and the "Cheddar Man" skeleton appeared in 1903 when the entrance to Skeleton Pit was being cleared. An archaeological dig by SANHS (R.F. Parry), 1927-30, proved a rich Cheddarian (Latest Palaeolithic, old "Magdalanian" or "Cresswellian") deposit with hundreds of flints in cave earth and scree, overlying stream-borne sand and pebble-beds and underlying cave earth with signs of Iron Age and Romano-British occupation. WCC dug 6 sites in the Boulder Chamber, 1960-65, in search of ancient upstream passage. The final shaft was abandoned when 30 feet deep and only 8 feet above resurgence level, due to frequent flooding.

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Cheddar Gorge - Cave Geology -

Great Oones Hole

This is in Cheddar Gorge, amongst trees on the left bank at the head of the slope, 160 feet above the coach park beside Cooper's Hole. The coach park and Cooper's Hole are well known to the public, but they are not generally aware of Great Oones Hole, up the cliff and inconspicuous from below. It is owned by Cheddar Caves Ltd., and there is occasional access.

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Cheddar Gorge - Cave Geology -

Cooper's Hole

Cooper's Hole cave in a car park in Cheddar Gorge, Mendip Hills, Somerset

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This is an easily-seen cave entrance in a car park, about 200 metres up the gorge from Gough's Cave (a little further up from the coach park). It is almost opposite Pride Evans Hole on the other bank of the gorge. It is an asphalted area, not picturesque (even with some graffiti), in the corner of the car park. Normally no entry is allowed and it is controlled by Cheddar Caves Ltd. A low level area beyond the railings was dug by MCG in 1959-1962. The southwestern passage sloped down 40 degrees in muddy scree, with a stalagmitic travertine layer, but is now largely flooded by road drainage and is largely choked (Barrington and Stanton, 1977). There is a south passage sloping up to a tight squeeze (Thynne Squeeze) and into a small muddy chamber. Some old steps were found to have been cut into the stalagmite slope (Barrington and Stanton, 1977).

The roof of the cave is evenly-bedded limestone, dipping at about 20 degrees in a direction southwest. This limestone is in the lower part of the (upper unit) of Clifton Down Limestone of calcite mudstone (i.e. micrite) type. Presumably the rather rectangular cave results from flow of water from the gorge into the rock at this small bend. The undissolved roof at the entrance is bedding-parallel, and is almost certainly the result of failure along a bedding plane (i.e. a bed of limestone has fallen). Like some other water-entry caves in the gorge, the cave is roungly rectangular in cross-section at the entrance and wider than higher.

Incidently the cave has been in use since the Iron Age (archaeological dig, 1931-32). There is also four feet of clay with charcoal beds, probably of lead smelting origin (Barrington and Stanton, 1977).

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Cheddar Gorge - Cave Geology -

Pride Evans Hole (easily seen)

This is in the cliff, 50ft or about 15 metres in the cliff above the road, and opposite Cooper's Hole (in the coach car park). It is obvious if you look up a bit and across the road from the coach car park. It is a short roomy cave that does not extend in for any significant distance. It was occupied by Mr. Pride Evans, the Welsh keeper of the Cheddar Pound, and his family in about 1810.

[A rather unlikely event occurred in this cave much later, according to the press. In 2013, a one kilogram, Second World War, German, cylindrical steel, incendiary device, dropped from a plane, was found in Pride Evans Hole by a ten year old girl, Lilymay Barnett. Lilymay and her father Steve took the rusted metal object into Derrick's Tea Room so as to enquire as what to do with it. A caver at nearby Gough's Cave then placed it for safety in a bucket of water. Fortunately no-one was harmed by the discovery of this historic device.]
[This story was reported in the Western Daily Press Online for 2013, item-18747295. http://www.westerndailypress.co.uk/Girl-10-finds-????-Cheddar-Gorge/story-18747295-detail/story.html]

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SOME MENDIP QUARRIES

MENDIP QUARRIES - GENERAL

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SOME MENDIP QUARRIES

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LOCATION:

Whatley Quarry - Introduction

Whatley Quarry, East Mendip Hills, Somerset, an overview

Whatley Quarry in Carboniferous Limestone, East Mendip Hills, Somerset, showing terraces

Whatley Quarry, grid reference ST731479, is a limestone quarry near the village of Whatley on the East Mendip Hills, Somerset. The quarry shows dark grey Carboniferous Limestone, mostly Black Rock Limestone, with a substantial part of lighter Clifton Down Limestone. There is a small area of overlying horizontally bedded buff-coloured Jurassic oolitic limestone forming an angular unconformity with the steeply-dipping Black Rock Limestone. There is much dolomitisation near the top of the Carboniferous limestone section. There are abundant near-vertical fissures and joints near top of limestone with karst weathering and minor pinnacle formation.

There is a visitor centre nearby at Moon's Hill Quarry and visits can be arranged to see Whatley Quarry. A few small parts can be visited directly but most is seen from a minibus driven down the quarry. This is very helpful but it is not easy to see details of the lithology or fauna.

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LOCATION:

Whatley Quarry - More Details

East face of Whatley Quarry, with a red unit, Mendip Hills, Somerset

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Whatley Quarry - Lake at the Base

Lake at the bottom of Whatley Quarry, East Mendip Hills, Somerset

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Whatley Quarry - Crushing and Transport

Crushed Carboniferous Limestone being supplied to tips at Whatley Quarry, East Mendip Hills, Somerset

Whatley Quarry, railway terminal, East Mendip Hills, Somerset

The Carboniferous Limestone is crushed and largely transported by rail. There is a special rail terminal at the quarry. The quarry is owned by Hanson plc and is linked by a freight only railway line (used by trains operated by Mendip Rail) to a junction with the Reading to Plymouth line at a junction near Frome station.

The quarry has been the object of protests against its impact on the environment and has had to appeal against planning application decisions because of the claimed derogation of river flows, groundwater abstractions and local springs due to historic dewatering associated with the quarry. Hanson runs a study centre, not far away at Moon's Hill Quarry.

A rather similar and large Carboniferous Limestone quarry is Torr Works quarry, nearby. This is at grid reference ST695446 and is at East Cranmore, near Shepton Mallet. It is also known as Merehead Quarry. Torr Works quarry site covers an area of some 200 hectares, including 60 hectares which have been landscaped to blend with the surrounding countryside. It is operated by the Aggregate Industries Company employing over 200 people and produces 6 million tonnes of limestone annually which is also carried directly from the quarry by Mendip Rail. (Data from Wikipedia.)

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LOCATION:

Whatley Quarry - Triassic Fissure Deposits

Calcite and dolomite in a vug that was originally an anhydrite nodule in a Triassic fissure fill, Whatley Quarry, Mendip Hills, Somerset

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CARBONIFEROUS LIMESTONE:

Torr Works Quarry - formerly Merehead Quarry, Eastern Mendip Hills

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Map showing Merehead Quarry in 1970, eastern Mendip Hills, Somerset

Location map showing the Torr Works Quarry or expanded Merehead Quarry in 2005, eastern Mendip Hills, Somerset

Comparison of the sections of Ordnance Survey maps above show the location and extent of the original Merehead Quarry in about 1970, before it became Torr Works. At that time it occupied only about a quarter of a square kilometre in area. However, it was already served by a railway line that has, no doubt, been of great benefit for regular export of aggregate and stone to southern England. Thus by 2005 it had become very successful and has expanded to area of about one and half kilometres. It is now as "Torr Works", much larger than most other quarries in the region.

Torr Quarry seen from the western side looking eastward, Mendip Hills, Somerset, 2010

Carboniferous Limestone in Torr Works Quarry or Merehead Quarry, eastern Mendip Hills, Somerset, 2010

Monument and viewport above Merehead or Torr Works Quarry, eastern Mendip Hills, Somerset, 2010

Notice at Torr Works Quarry, Mendip Hills, Somerset, showing future plans

It is a very large limestone quarry occupying about one and a half square kilometres. It has been worked into south-dipping Carboniferous Limestone. The entrance to this quarry is very conspicuous from the main A361 Frome to Shepton Mallet road. You approach it, usually quite rapidly, in a dip and curve of the main road. You see a large sign with the words "Torr" and a Union Flag is usually flying from a nearby flagpost. This entrance is just to the east of East Cranmore.

The quarry is not very easy to see on foot but there are footpaths around it. There is quite a long bridleway from Downhead along the northwestern side and round to the southwest of the quarry. The quarry, although very large, is not easily seen, being rather concealed and inaccessible with a combination of wire fencing, a line of small trees and an internal road and bank. Its long term prospects for geological conservation may not necessarily promising because its upper slopes may be smoothed over, rather than preserving bold limestone cliffs. However, details are not known, and the ending of the quarrying is a long time ahead. There is still plenty of limestone; the Black Rock Limestone can be up to 300m thick and is buried beneath the southern end of the quarry. When the quarrying does end, according to a notice, the lower part will be allowed to flood and it will make a large and pleasant lake.

The Carboniferous Limestone is on the south limb of the Beacon Hill Pericline, and dips south at a moderate angle. It is to some extent red-stained by formerly overlying Triassic strata.

With regard to the Wessex coast, the quarry is of interest in that it might be the source of much of the Carboniferous rock armour used for sea defences. This type of rock armour can be seen at Barton-on-Sea and Hurst Spit for example. Information on this rock armour is provided further below, in the present website.

For more information on Torr Works Quarry see the BGS website: Torr Works and Asham Wood.

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LOCATION:
TORR WORKS QUARRY:

Carboniferous Limestone - Details

Black Rock Limestone, Carboniferous, in the northeastern part of Torr Works Quarry, eastern Mendip Hills, Somerset, 2010

A modified geological map of Torr Works Quarry or Merehead Quarry, eastern Mendip Hills, Somerset

For geological information on the area purchase the British Geological Survey, Frome Sheet, No. 281 from the BGS Bookshop online (at present only 12 pounds sterling). The small map above shows a modified and partly redrawn version of just a small part of this map. The quarry is shown by BGS as almost entirely within Carboniferous Limestone, of Mississipian or Lower Carboniferous age. This limestone, which contains many corals and brachiopods, originated in a near-equatorial, warm and shallow sea, about 345 million years ago. The local names such as Black Rock Limestone Formation, Vallis Limestone Formation, Clifton Down Limestone Formation are subdivisions of the Carboniferous Limestone.

The dip is round about 40 degrees towards the south but varies a little over quarry area. Because there is only a moderate dip and because the limestone is thick, it occupies a substantial area. Thus the quarry has been able to expand (unlike Whatley Quarry) to more than one and half kilometres from north to south. It is limited by low ground and change of geological outcrop to the south. It would be restricted in extent by a fault, the Downhead Fault to the west. In theory, but perhaps not in reality for conservation reasons, the quarry could expand to the northeast to take in Asham Wood. There is more Black Rock Limestone in that direction.

There is only one significant fault in the quarry, as shown by the British Geological Survey map, Frome Sheet, 281. This fault is in the southern part, just south of the lake at the base. It crosses the quarry in an east-west direction and downthrows on the north side. The fault is not major and does not change the pattern of outcrop very much. The main part of the quarry seems unfaulted. There is a major fault, the Downhead Fault which is almost parallel to the western margin of the quarry but is beyond it, to the west and near the road to Downhead. This does not affect the quarry. Just south of the quarry, almost on the route of the major road, is the Cranmore Fault, which trends roughly east west (its line is just north of East Cranmore).

Because of this fairly uniform southerly dip the Torr Works Quarry has older Carboniferous Limestone in the northern half. This is of Black Rock Limestone, Courceyan and Chadian in age (i.e. it belongs to the lower part of the Lower Carboniferous). It can attain a thickness of 300 metres and is the thickest of the major subdivisions of the Carboniferous Limestone. The Black Rock Limestone in this part of the Mendips is a dark-coloured carbonate wackestone or packstone, using Dunham's classification (Green, 1992). This means that it usually consists of carbonate allochems ("grains") in a fine grained matrix (either supported by matrix or grains). The microscopic structure of a rock of this type is not likely to be very obvious in the field, even with a handlens. South of that (and just north of the lake) is Vallis Limestone which is Arundian. This is just a narrow belt. The Vallis Limestone is lighter-coloured and is a bioclastic grainstone and packstone (i.e. of shell fragments with or without fine matrix).

Carboniferous Limestone, Clifton Down Limestone,  dipping south and striking east-west, Torr Works Quarry or Merehead Quarry, Mendip Hills, Somerset, 2010

The lake area and the works are on Clifton Down limestone which is Holkerian in age. This can vary from grainstone to calcite-dolomite mudstone. Some sedimentary features of this are shown in the section which follows below.

The Hotwells Limestone (Asbian and Brigantian is beyond the quarry at the hill to the southeast.

More details, including a large scale map of part of the Heale to Downhead area at the margin of the quarry, are available in (Welch, 1933).

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TORR WORKS CARBONIFEROUS LIMESTONE ROCK ARMOUR AT BARTON continued

Rock-Armour - Carboniferous Limestone Blocks

Large blocks of limestone from the Merehead or Torr Works Quarry are easily accessible at the shore of Barton-on-Sea, Hampshire. They have been used successfully for sea defence rock armour (armour-rock or armor-rock). The blocks are used in various places in the sea defences but are best observed where they have become scoured clean by the abrasive action of beach material which attacks them during storms.

Fortunately, the blocks have been studied and described, with regard to fossils, in a paper by Lewis et al. (2003). They gave details of the geology of this rock-armour, and in particular the content of fossil echinoderms. The stone was quarried at Merehead Quarry when it was under the ownership of Foster Yeoman, before it became Torr Works. The large limestone blocks were transported from there to Barton, not by train (in spite of the railhead) but by flat-bed lorry, according to Professor Andrew Bradbury, the Coastal Projects Manager of Hampshire County Council.

Crinoid ossicles in Carboniferous Limestone rock armour at Barton-on-Sea, probably Clifton Down Limestone from Merehead or Torr Works Quarry, eastern Mendips

The tabulate coral Syringopora in Carboniferous Limestone rock armour at Barton-on-Sea, Hampshire

Lithostrotion in Clifton Down Limestone, Carboniferous rock armour from Torr Quarry, at Barton-on-Sea, Hampshire

The rock type containing fossils at Barton-on-Sea is Clifton Down Limestone, Devensian, Holkerian (Carboniferous Limestone, Mississipian) according to Lewis, Donovan and Sawford (2003). They reported a rich fauna of echinoderms, corals, bryozoans, trilobites, brachiopods and gastropods. The echinoderms include plates of the tests of the echinoids Palaechinus sp., Archaeocidaris sp. and an indeterminate echinoid. Numerous crinoid ossicles are present and calyces have been found of the crinoids Platycrinitid sp., Actinocrinus sp. aff. A. rotundatus Wright, monobathrid sp. indet., camerate sp. indet. and Taxocrinus sp.

Carboniferous rock armour has been used at Lepe Beach, Hampshire and see this webpage for further information.

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TORR WORKS CARBONIFEROUS LIMESTONE AT BARTON

Carboniferous Limestone - Triassic Fissure Fills

A fissure fill with calcite and yellow sediment in a Carboniferous Limestone block at Barton-on-Sea, Hampshire

Red siltstone filling an extensional fissure system in Carboniferous Limestone rock armour at Lepe Beach, Hampshire (neptunean dyke)

Interesting fissure fills ("neptunian dykes") with red and yellow sediment occur in the blocks of Carboniferous Limestone at Barton-on-Sea. See the paper of Wall and Jenkyns (2004) for a discussion of the origin of sediment-filled fissures in the Carboniferous Limestone of the Mendip Hills. Another example from similar Carboniferous rock armour at Lepe Beach is also shown for comparison.

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LOCATION:

TORR WORKS, CARBONIFEROUS LIMESTONE AT BARTON continued

Rock-Armour - Replaced Evaporites

Calcite pseudomorphs after halite and calcite-replaced anhydrite or gypsum nodules in rock armour, Barton-on-Sea, Hampshire

At Barton-on-Sea, Hampshire, Carboniferous rock armour is of special interest in containing evaporites. This rock armour with evaporites is almost completely unfossiliferous and is darker in colour than the associated fossiliferous limestone from Clifton Down Limestone. It may be dolomite but has not been examined in the laboratory. This unusual limestone is present as rock armour at the shore just east of Hoskin's Gap, Barton-on-Sea. is examined at low tide. It needs to be examined at low tide because high tide or a stormy sea will cause wave wash over these rocks.

Particularly conspicuous in an unfossiliferous dolomite (or limestone) are good calcite pseudomorphs after halite. Some of these are feathery or skeletal. They have all formed in the carbonate sediment when it dried out with a content of very hypersaline (near 350 ppt) brine. Associated with the halite is much nodular calcium sulphate replaced by calcite. This may have originated as gypsum, but in proximity to so much halite it is almost certain that it was changed diagenetically to anhydrite at an early stage.

Calcitised nodular anhydrite or gypsum in a dolomite or dolomitised limestone of sabkha facies, and used in sea defences, Barton-on-Sea, Hampshire

Recent nodules of anhydrite, one with chicken wire structure, Dukhan Sabkha, Qatar

Go to the Qatar Sabkhas webpage to see more on modern analogues.

With regard to the Carboniferous Limestone of Britain and Ireland, evaporites occur in several places. They occur in the Visean (Upper Dinantian) in County Leitrim, Ireland ( West, Brandon and Smith, 1968). These are younger than the Holkerian Clifton Down Limestone, from which the associated fossiliferous rock armour of Barton-on-Sea has come. Evaporite facies have also been found in County Carlow, Ireland ( Nagy et al., 2005). Evaporites have also been found in the Main Limestone of the Lower Carboniferous in South Wales (Bhatt, 1975). A major Carboniferous evaporite deposit, the Hathern Anhydrite, occurs underground in Leicestershire (Llewellyn and Stabbins, 1970). There are traces of evaporites in the Lower Carboniferous elsewhere in Britain, but they have not necessarily all been reported in the literature.

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SILURIAN ANDESITE


LOCATION:

Moon's Hill Quarry - Introduction - Location

Somerset Earth Science Centre, Moon's Hill Quarry, eastern Mendip Hills, Somerset, 2010

Near the entrance to Moon's Hill Quarry is the Somerset Earth Science Centre (telephone 01749-840156, email info@earthsciencecentre.org.uk). This is an educational centre with rock and mineral specimens, with staff who explain the quarrying and take minibus tours of Moon's Hill and Whatley Quarry. This centre is supported by the quarrying industry. There are, of course, strict Health and Safety regulations and restrictions regarding the working quarries. Access is controlled and guided and limited to certain areas, and appropriate hard hats and high-vis jackets have to be worn. The working quarries discussed below are not places for casual visits and it may not necessarily be possible to obtain any close view of certain stratigraphical units.

New topographic map showing the quarries northeast of Shepton Malley, Mendip Hills, Somerset

An old map of the Silurian Inlier of the Mendip Hills, Somerset, by Reynolds in 1907

Moon's Hill Quarry is deep quarry in the eastern Mendips, near Stoke St. Michael and northeast of Shepton Mallet. The main purpose of the quarry is to produce good aggregate from hard Silurian andesitic rocks. The quality and resistance to wear of the volcanic material is the reason why the quarry is situated on the limited Silurian outcrop of the eastern Mendip Hills.

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INTRODUCTION:

MOON'S HILL VOLCANIC ROCKS AND QUARRY

Moon's Hill Quarry near Shepton Mallet in the eastern Mendips provides an unusual exposure of Silurian volcanic rocks. The exposures are in a deep quarry, descending in a series of terraces. This webpage provides only a brief introduction to what is seen on a visit to the top of the quarry. Access to the lower parts is not easy because of reasons of Health and Safety regulations in a working quarry. Therefore, the features shown here, and mainly of the volcanic conglomerate, may not be typical of the exposure, and do not include much evidence of the lavas or dykes.

Van De Kemp (1969) commented that there are probably 15 or more rock units in the series, including andesite and rhyodacite lavas, rhyodacite tuffs, "agglomerate", and a dolerite dyke. The predominant rock type is rhyodacite which may be as much as 80 percent of the volcanics. The individual rock units cannot easily be recognised in the overview photographs which follow. The close-up photographs mainly illustrate a volcaniclastic conglomerate. The individual clasts are very rounded and not conspicuously vesicular. Furthermore they are associated with a cross-bedded, reworked tuff showing the action of water.

There is an excellent, educational visitor centre close to the quarry. This facility can arrange visits both to this quarry and to Whatley Quarry, although that direct access to the rock faces is limited to certain areas at the top.

Moon's Hill Quarry in Silurian andesite and volcaniclastic conglomerate, Mendip Hills, Somerset, a general overview, 2010

The bottom of Moon's Hill Quarry in Silurian andesitic volcanics and volcaniclastic conglomerate, Mendip Hills, Somerset, seen from the viewing platform

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MOON'S HILL QUARRY continued:

Volcaniclastic Conglomerate - Rounded Clasts

Quarry debris, showing rounded clasts, at Moon's Hill Quarry, Silurian volcanics, Mendip Hills, Somerset, 2010

The above photograph shows the location at the start of a guided tour of part of Moon's Hill Quarry. We are at the southeastern corner and looking northwest towards the crushing and sorting machinery of the quarry. Compare the field photograph with the aerial photograph. We are going to go down through the gap in front to a cliff face of volcaniclastic conglomerate at the uppermost terrace.

Vertically orientated conglomerate or agglomerate at Moon's Hill Quarry, Mendip Hills, Somerset, 2010

The view now is of the uppermost cliff and uppermost terrace in the southeastern part of Moon's Hill Quarry. This area is away from the main working face of the quarry so access, under guidance, can be permitted here. The cliff appears at first sight to consist of brown rubble. Closer examination suggests that it is a degraded, partially decomposed conglomerate of volcaniclastic origin.

Volcaniclastic conglomerate block, Silurian, Moon's Hill Quarry, Mendip Hills, Somerset

Recent spheroidal weathing of a rounded clast, Silurian volcanics, Moon's Hill Quarry, eastern Mendip Hills, Somerset

A peculiarity of the volcanic material seen at the top of the quarry is that the clasts are very well-rounded. This was regarded for a long time as a volcaniclastic conglomerate since its description by Professor Sidney Reynolds (1907), or earlier. The clasts were regarded as rounded pebbles of volcanic rock. In modern terminology it is a volcaniclastic conglomerate of epiclastic type (according to the classification given by Dorrik Stow (2005).

However, it should be noted that for a time there was a different view of the origin. Van De Kemp (1969) referred to the rounded clasts as "abundant bombs in ash matrix" and Ponsford (1970) then stated that the deposit should be termed an "agglomerate". Ponsford (1970) drew attention to Dr Doris Reynolds' (1969) suggestion that they were rounded by fluidisation within the vent.

This does not seem a very likely explanation in this case. The association with beds of tuff, apparently reworked by water and apparently fining-upward beds, seems to support a volcaniclastic conglomerate origin. The rounded clasts do not appear to be volcanic bombs.

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MOON'S HILL QUARRY continued

Water-reworking of Tuff

Moon's Hill Quarry, Somerset, Silurian volcanics, a finer bed and two fining-upward units

Laminated tuff with some ripple cross-lamination, Moon's Hill Quarry, Mendip Hills, Somerset

Cross-laminated, reworked tuff, Silurian volcanics, Moon's Hill Quarry, Mendip Hills, Somerset

At the top of Moon's Hill quarry there is evidence of reworking of tuffs presumably by water (although possibly by wind). This seem to support the view that the coarser deposits, although of volcanic origin have been reworked by water and that this is the reason for the roundness of the clasts. However, no detailed study has been made and this may not necessarily be correct.

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MOON'S HILL QUARRY

Andesite

A block of vesicular andesite, Moon's Hill Quarry, Mendip Hills, Somerset

Shown above is an isolated block of andesite, ex-situ. It has probably been brought up from a lower part of the quarry for display purposes. This andesite is vesicular.

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MOON'S HILL COMPARISON - Volcanic Rocks

Mount St. Helens

Mount St  Helens with andesite, dacite and basalt and much tephra, Washington, USA, for comparison with the igneous rocks of Moon's Hill Quarry, eastern Mendips, England

The Silurian igneous rocks of the Mendip Hills are the remains of a vent of a volcano associated with subduction near a plate margin. A broad comparison can be made with the famous volcano, Mount St. Helens, Washington State, USA. This also contains andesites and large quantities of pyroclastics. The general compositional trend of Mount St. Helens has been from rhyodacite to andesite ( Hopson and Melson, 1990) and there is general similarity to these Silurian volcanics.

Of course, the place looks nothing like Mount St. Helens, with the green fields of agricultural land around a subdued but hilly topography. Beneath the surface, though, the record is that of a great volcano, probably associated with subduction. A complication is that the Moon's Hill volcano has been turned on its side by major earth movements and thus the strata are approximately vertical in orientation. It has also been extensively sheared by thrusts and the near-surface part is badly weathered.

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MOON'S HILL QUARRY - DEVONIAN

Portishead Formation

Portishead Formation, Devonian, Moon's Hill Quarry, eastern Mendip Hills, Somerset, 2010

At the northern edge of Moon's Hill Quarry there is an exposure of the Portishead Formation. This is Upper Devonian strata, consisting of reddish-brown sandstones (Old Red Sandstone). The photograph above shows it at a distance from the southern side of the quarry. The details were not seen and it is not known whether the basal conglomerates is present here in addition to sandstones. The general red sandstone facies is fluvial, a continental facies (for marine Devonian see Torquay webpage.

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ACKNOWLEDGEMENTS

I am very grateful to the members of the Open University Geological Society who participated in a field trip to Moon's Hill and Whatley Quarries in August 2010. I much appreciate the organisation of this field trip by Jeremy Cranmer. Hugh Prudden, the geological expert on the region, kindly sent me a list of references and details of websites. I am much obliged to him for his help. The staff of the visitor centre at Moon's Hill Quarry provided an excellent tour with explanation of features in both Moon's Hill Quarry and Whatley Quarry.

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REFERENCES AND BIBLIOGRAPHY
(This is being expanded progressively, from time to time. It also, for the author's convenience, intentionally lists some Lower Carboniferous publications on areas beyond the Mendip Hills, including the Tweed Borehole)


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Alabaster, C.J. 1974. Some Copper, Lead and Manganese minerals from Merehead Quarry, East Mendip. Proceedings of the Bristol Naturalists Society.


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Al-Jasser, S.H. and Hawkins, A.B. 1979. Geotechnical Properties Of The Carboniferous Limestone of The Bristol Area; The Influence Of Petrography And Chemistry. International Society for Rock Mechanics. 4th ISRM Congress, Montreux, Switzerland. 1979. Authors: S.H. Al-Jassar (Geology Department, University of Bristol) and A.B. Hawkins (Geology Department, University of Bristol). [The paper can be purchased online]
Abstract:
The Carboniferous Limestone consists of eight lithologies: shelly, crinoidal, oolitic, micritic, dolomite and impure limestones, siliceous sandstone and mudstone. Samples of these rock types, apart from the mudstone, have been collected, sectioned, described in detail, the nine major elements determined, and the insoluble residue analysed by X-ray diffraction. Among the tests performed were unconfined compressive strength and modulus of elasticity measured parallel, vertical and oblique to the bedding: triaxial tests: two cycles of loading and unloading, taken to failure: point load tests on various sized samples: Schmidt hammer tests parallel and vertical to the bedding, in the field and laboratory. A relationship can be shown to exist between the geotechnical properties and these with the petrography and chemistry of the rocks.
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[Example extract:] 2. Background Geology.
The dominantly marine 1000 m thick Carboniferous Limestone succession, deposited about 340 m years ago, is underlain in the Bristol area by the continental Devonian (Old Red Sandstone) and overlain by the deltaic and fresh-water sequences of the Millstone Grit and Coal Measures. The basal beds, the Lower Limestone Shale Group, are a diachronous littoral sediment consisting of heavily overconsolidated mudstones (shales), limestones and occasional sandstones. The overlying Black Rock and Clifton Down Groups consist dominantly of calcareous strata except for the Clifton Down Mudstone which follows a break in sequence (known locally as the Mid-Avonian Break) and the calcareous/arenaceous/ argillaceous sediments of the Lower Cromhall Sandstone. In the overlying Hotwells Group the arenaceous and argillaceous sediments increase in thickness until they pass, without a stratigraphic break, into the Millstone Grit (known locally as the Quartzitic Sandstone Group). During the Variscan (Hercynian, Armorican, Permo-Carboniferous) Orogeny the area suffered two periods of compressional stress, the first dominantly westwards, causing north to south trending folds best developed north of Bristol, and the later northwards producing east to west structures such as the Mendip Hills south of Bristol. As a result of these stresses the rocks of the area were tilted and in places even overfolded; in many places there are major thrust fault movements and locally within the limestones the formation of stylolites.


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Atkinson, T.C., Smart, P.L. and Atkinson, J.N. 1884. Uranium-Series dating of speleothems from Mendip Caves: 1. Rhino Rift, Charterhouse-on-Mendip. NGR ST4847.5557. Altitude 210m. Length 320m. Vertical Range 144m. Proceedings of the University of Bristol Speleological Society, 1984, vol. 17, part 1, pp. 55-69. Available in full online as a pdf file.
Abstract:
The morphology and deposits of Rhino Rift are described. The cave is an 'invasion vadose cave' formed when the local saturation level was 75-90 m. O.D. Ten U-series dates on four speleothems show that a boulder and cobble infill at the bottom of the known cave accumulated sometime after c. 45,000 years ago, whereas poorly sorted gravels blocking the cave passages were laid down before about 11,000 years ago. The cave itself was formed before 75,000 years ago, probably during isotope stage 5 or 6. The implications for the geology of the Mendip region are discussed.
Fig. 15 shows and extended section, redrawn after Stanton. Fig. shows details of sectioned speleothems. Table 1 gives speleothem age data. On pp. 66-67, the relationship to Cheddar Gorge caves is briefly discussed.


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Bamber, A.E. 1924. The Avonian of the Western Mendips from the Cheddar Valley Railway to the Sea, West of Brean Down. Proceedings of the Bristol Naturalists' Society, vol. 6, part 1, 75-91. By Miss Agnes Elizabeth Bamber, M.Sc, F.G.S. [Also an abstract is given in the Quarterly Journal of the Geological Society, vol. 80., pp. 182-3.]
Contents:
1. Introduction; (a) Previous Work; (b) Geographical Extent.
2. Geological, Structure and Physical Features.
3. Description of the Zones; (a) Surface Extent and Lithological Characters; (b) Faunal Lists and Notes.
4. Description of the Best Exposures.
5. List of the Chief Exposures.
6. Comparison of the Avonian of the Western Mendips with; (a) The Avon Section; (b) Burrington Combe.
7. Conclusions.
[This paper has much good faunal and zonal information and discusses various exposures. It is not specifically on Cheddar Gorge.]
Note particularly:
"(b) Geographical Extent.
The area is 9 miles long in an E. to W. direction, and has a maximum width of "2J" [the computer text is erroneous here - is this 27, 22 or 21 or what?] miles in a N. and S. direction. It forms the western portion of the Mendip uplift. It includes five isolated Carboniferous inliers, which passing from west to east are as follows:
(1) Brean Down.
(2) Uphill.
(3) Bleadon Hill.
(4) Banwell Hill.
(5) Wavering Down.
Along the northern side of our region are the villages of Banwell, Hutton and Uphill, and on the southern side those of Bleadon, Loxton, Compton Bishop and Cross. On the E., in the Triassic ... [continues].]

Bamber, A.E. 1924. The Avonian of the Western Mendips, from the Cheddar Valley Railway to the Sea, West of Brean Down. The Avonian of the Western Mendips, from the Cheddar Valley Railway to the Sea, West of Brean Down. Quarterly Journal of the Geological Society, vol. 80, pp. 182-183. January 1924. [this is probably just an abstract - it is only one page. The full paper is in the Proceedings of the Bristol Naturalists' Society. See above, and is available as text online.]
Abstract:
In this paper a comparison is made between the Avonian of the Western Mendips and (a) the Avon Section and (b) the Burrington Combe section. The outcrops of the Carboniferous Limestone zones, classified according to the notation of the late Dr. A. Vaughan, have been mapped. Levels from K2 to S1 are exposed in the area. The lithological and palaeontological characters of the zones are described. Considerable faulting and folding occurs, more especially in the west of the region.

Bamber, A.E. 1924. Some episodes in the geological history of the south of England. Quarterly Journal of the Geological Society, vol. 98.

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Barrington, N. and Stanton, W. 1977. Mendip: The Complete Caves and a View of the Hills. Cheddar Valley Press. 236pp. Sturdy, paperback book of large pocket size and quite thick. By Nicholas Barrington and William Stanton. Published by Barton Productions in conjunction with Cheddar Valley Press, Cliff Street, Cheddar, Somerset. ISBN 0 9501459 2 0, Printed in England by Dawson and Goodall, Ltd. Bath. Third Revised Edition, 1977. The caves are listed alphabetically with accounts ranging from a short summary to several pages of description. Each cave has a reference number. There are a large number of caves in Cheddar Gorge and the subject is not simple to deal with. There is a descriptive section on: Evolution of the Mendip Landscape, on pages 215 to 225. There are many photographs, mostly not good quality as prints, but very interesting. There are some older, historic photographs on pages 184-192. The book includes a small simple map of Cheddar Gorge with more than 40 numbered caves. There does not seem to be any large, good quality map of Cheddar Gorge. The book, or at least the third, revised edition is non-metric. Although, it is, of course, written for the caver, it provides useful information to the geologist. It is, well-worth purchasing for its important descriptive data and history, in addition to the photographs.


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BGS - British Geological Survey . 2010? The Rocks of Mendip. Go to website: The Rocks of Mendip.
"Silurian rocks (444 to 416 million years ago) The Silurian rocks of the Mendips are formally known as the Coalbrookdale Formation, and occur as a narrow elongated outcrop in the core of the eroded anticlinal fold that forms Beacon Hill, north-east of Shepton Mallet. The rocks comprise a sequence of fissile mudstones ('Wenlock Shales') around 600 m thick overlain by an interbedded succession of tuffs, agglomerates and andesite lava flows. A vent agglomerate represents a section through an ancient volcanic fissure, fortuitously exposed at the surface because of the almost vertical dip of the strata. Volcanic rocks are rare in the Silurian, and the Mendips are one of the few places in the UK where they can be observed." [continues.. good website!]

BGS (British Geological Survey). BGS website: Torr Works and Asham Wood.

BGS (British Geological Survey). BGS website: History - East Mendip Quarries.
Example extract:
By 1957, Foster Yeoman, having largely completed the upgrading of Dulcote Quarry, near Wells, took over Merehead from Limmer with 150 acres of reserves at a cost of only 15 000 pounds. .... By 1967, output had increased to a quarter of a million tonnes annually. New, larger gyratory crushers were installed in 1969, the Norberg being one of the largest in Europe. These raised output rapidly to 3 million tonnes in 1971 and 5 million tonnes in 1973 (with potential capacity of 7 million tonnes a year), making the quarry the largest single producer of aggregates in Europe. ..
The quarry itself was working through steeply dipping beds 20 degrees to 40 degrees (occasionally with cavities) forming the southern limb of Beacon Hill Pericline. The western border of the quarry is parallel to the Downhead - East Cranmore road immediately to the west of which is the major Downhead Fault which marks the termination of the Carboniferous Limestone in this direction.
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Bhatt, J. 1975. Evidence of evaporite deposition in the Lower Carboniferous Main Limestone Series of South Wales, U.K. Sedimentary Geology, vol. 13, issue 1, March 1975, pp. 65-70.
Abstract:
Petrographic examination of the dolomitized Main Limestone Series cropping out in the south, east and northeast corners of the South Wales Coalfield Basin shows evidence of the earlier presence of evaporite minerals. However, it is believed that lack of extensive evaporite deposits in these rocks may be due to the active diagenetic dissolution and oncoming humid coal conditions of post Main Limestone time. The evaporite minerals in the Main Limestone rocks seem to be overwhelmingly early diagenetic in origin in the light of the following observations: (1) calcite or dolomite pseudomorphs after gypsum crystals associated with a fine pelmicrite matrix; (2) association of such pseudomorphs with oolitic pelsparite; and (3) evaporite solution breccia texture.
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Carter, L. 2014. [by Linda Carter]. Cheddar Gorge and Caves. 58 pp. illustrated and including a reference list. Paperback. Somerset Archaeological and Natural History Society. This can be purchased at the Cheddar Gorge shops for 4.99 pounds only.


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Chadwick, R. A. 1986. Extension tectonics in the Wessex Basin, southern England. Journal of the Geological Society, vol. 143, pp. 465-488.
Abstract
The Permian to Cretaceous tectonic evolution of the Wessex Basin was controlled by horizontal tensional and vertical isostatic forces within the lithosphere. The gross morphologies of its constituent structures were governed by the location of Variscan thrust and wrench faults in the upper and middle crust, which suffered extensional reactivation in tensional stress fields oriented approximately NW-SE. Several episodes of crustal extension can be resolved, in early Permian, early Triassic, early Jurassic and late Jurassic/early Cretaceous times. These were characterized by the rapid subsidence of fault-bounded basins and commonly, by erosion of adjacent upfaulted blocks. Superimposed upon the fault-controlled subsidence, dominant during periods of fault quiescence, and becoming increasingly important with time, a component of regional subsidence is considered to have a thermal origin. This suggests that crustal extension was accompanied by some form of, not necessarily uniform, lithospheric thinning. Subsidence analyses assuming local Airey isostasy give cumulative crustal extension factors of 20–28% beneath the grabens. A more reasonable assumption of regional Airey compensation indicates basinwide crustal extension of 13–17%. which is consistent with BIRPS offshore deep seismic reflection data.


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Donovan, D.T. 1969. Written discussion to paper taken as read (Ford and Stanton]: 6th September, 1968: [see: Ford D.C. and Stanton, W.I., 1969.] Proceedings of the Geologists' Association, 1969, vol. 80, pp. 379-380.
[Extract from the last part of the one page discussion:
"Regarding the regional chronology, I believe that extreme caution is necessary. When the erosional benches along the southern flanks of the Mendips are described (pp. 409-411) no mention is made of their origin. On pages 423-5 the benches are correlated, tentatively, with the Mediterranean Pleistocene sea-levels. Do the authors believe these benches to be marine erosion platforms? This seems a difficult interpretation in view of the altitudinal range of features in some groups - for example, the Warren Hill Bench is based on only four features ranging in height from 220 to 270 ft. O.D. In any case, are not the successive lower levels of water outlet from the limestone, demonstrated by the authors, likely to have been determined by the extent of removal of the soft Mesozoic rocks which once filled the Somerset levels?"
[Part of the reply by Ford on p. 380:]
"As regards the erosional benches on the southern flank of the Mendip Hills, those at 70ft (21m.) and 120-140ft (37-43m.) ('Axe Bench') are quite likely to be of marine origin. It is agreed that the higher remnants are poor evidence. They should only be taken to indicate that exhumation of the flank was most probably intermittent. The regional correlation must certainly be approached with the caution that Professor Donovan recommends. It was only with reluctance that the tentative chronology (Table III, p. 425, of our paper), was inserted by the undersigned - who now considers it a grave error to have used the Mediterranean eustatic fram at all. What is impressive in central Mendip is the rhythmic succession of erosional and depositional phases of comparable scales, within the caverns, and their apparent relation to valley-deepening events at the surface. In truth, our pre-Wurm chronology is scarely more than an emphasis of this rhythm. The older cave-fills lack fossil fauna and other characteristics of visible size, but contain several distinct stalagmite horizons. Our research group at McMaster University has some hopes of dating the stalagmite by radiometric means. This may put the chronological speculation on an altogether firmer footing."


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Ford, D.C. 1965. The origin of limestone caverns: a model from the central Mendip Hills, England. Bulletin of the National Speleological Society of America. Vol. 27, pp. 109-132. By Derek C. Ford of McMaster University, Hamilton, Ontario, Canada.

Ford, D.C. and Stanton, W.I. 1969. The geomorphology of the central Mendip hills. Proceedings of the Geologists' Association, vol. 79, pp. 401-427. [A full copy of the paper can be purchased from the Geologists' Association. See details online.]
Abstract:
The Hills, consisting mainly of cavernous Carboniferous Limestone, form a gently rolling plateau surface at 800 to 850 ft. (245260 m.) O. D. Several monadnocks of Old Red Sandstone stand up to 200 ft. (60 m.) higher. The steep south flank of the plateau extends nearly down to sea-level and is basically a Triassic feature exhumed from beneath soft Mesozoic strata. The plateau, on the other hand, is thought to be largely a subaerial erosion surface of late Pliocene date.
Six erosion benches are recognised on the south flank between 670 ft. (205 m.) and 70 ft. (21 m.) O.D. They reflect the intermittently falling Pleistocene sea-level, and may be correlated with Zenner's eustatic levels from the Calabrian to the Main Monastirian [although see Donovan's discussion on this, and Ford's reply - the matter is questioned.]. A more irregular bench in the east is a structural feature developed at the base of the Lower Lias Clay.
A system of dry valleys similar in pattern to normal river systems is entrenched into the plateau. The original drainage pattern on the plateau surface was directed southwest or south, probably superimposed from a Miocene dome of Chalk. Entrenchment at the start of the present erosion cycle soon brought adjustment to the Palaeozoic structure. The Cheddar proto-system, closest to the Bristol Channel, had base-level advantage and beheaded most of the others.
The valleys debouch through gorges cut in the south flank. The size of the gorges varies according to the size of their fossil catchments. Changes of gradient in the thalwegs are due to a succession of knickpoints receding from the south flank baselevels. Valleys and gorges were incised by surface streams; the upper parts in the late Pliocene and early Pleistocene before drainage had gone underground, the lower parts when streams returned to the surface on Ice Age permafrost.
Underground drainage gravitated toward the lowest limestone outcrops. The two main springs are located at the mouths of the two main gorges, Cheddar and Ebbor. Ancient water tables traced in the dry springhead caves can be correlated with the erosion benches.
Most of the hundreds of closed depressions or dolines on the limestone plateau were created by solution working down from the surface. Also on the plateau are eighteen internally draining karst basins up to 50 ft. (15 m.) deep and 300 acres (1.2 km.2) in area. They developed at various stages of the Pleistocene by desiccation of headwater valleys. The older examples have a complex history and supported lakes on permafrost during glacial periods. Most show one or more overspill channels.
[See also discussion by Donovan, and reply by Ford, referred to above]


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Ford, T.D. 2002. Dolomitization of the Carboniferous Limestone of the Peak District: a Review. Mercian Geologist. East Midlands Geological Society. By Trevor D. Ford.
Abstract. Large areas of the Carboniferous Limestone of the southern Peak District have been dolomitized, particularly the more coarse-grained calcarenitic facies. After a summary of the physical features of dolomitized limestone, its stratigraphic distribution and relationship to mineralization, the evidence points to a late Carboniferous date of dolomitization. Possible sources of the magnesium are from buried shales in adjacent basins, effectively as an early flush of hydrothermal fluids, from altered mafic minerals in volcanic rocks or both. It is proposed that a magnesium-rich fluid moved ahead of the hydrothermal mineral fluids and was exhausted before the mineral veins were infilled.

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George - Professor Thomas Neville George, FRS. 1904-1980.
Generally known as Professor Neville George. President of the Geological Society of London. Awarded the Lyell Medal in 1963. He was born in Swansea and had South Wales geological interests, amongst others. He was Professor of Geology at Glasgow University.
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George, T.N. 1972. [T. Neville George]. The Classification of Avonian Limestones. President's Anniversary Address for 1970, Geological Society of London. Journal of the Geological Society of London, vol. 128, pp; 221-256. The paper here is very good and was a classic paper of the time, although the terminology of the Lower Carboniferous is different now. It deals with the Carboniferous Limestone from South Wales to the Mendip Hills and includes much petrographic and facies data. It is very good and still relevant but the reader needs to have some familiarity with older terminology of "S2 and C2S1" "zones" etc. Amongst other matters, he found traces of evaporites in the Lower Carboniferous of the southern UK. ]
Abstract:
In systematised stratigraphical classification 'Avonian' is a term junior to 'Dinantian'; but its present ignorance of the precise correlation equivalents of Dinantian assises ["assises" - two or more beds of strata united by fossils of the same characteristic species or genera] and Avonian zones the term is conveniently retained for the Lower Carboniferous rocks, most of them typical 'Carboniferous Limestone', of the British South-Western Province, where there is also ignorance of the precise horizons of the Fammennian-Dinantian junction and the Dinantian-Namurian junction. At the same time, the Avonian assemblage zones have significance only in the carbonate rocks of the northern part of the Province; they are not applicable to the Lower Culm of the southern part, and they are applicable only with uncertainty to other Lower Carboniferous provinces in Britain. 'Avonian' is of only temporary and local validity: it is not the name of a standard series.
Avonian rocks are mainly shelf limestones of a variety of kinds. They display marked lateral and sequential changes that reflect the influence of many factors, of which contemporary earth-movement, with consequence migration of facies belts and the occurrence of sharp lithological breaks and non-sequences, was of major importance. The fossiliferous members of the series reflect subtly variant biotopes that throw light on a multiplicity of shelf environments whose characteristics and distribution have strong analogies, in association of organisms and in community balance, with near-shore shelf sediments of many of the warmer present-day aeas; and recurrent inorganic limestones (mainly calcite muds and oolites) demonstrate the general shallowness of the shelf seas over very wide areas. Detailed palaeogeographical reconstruction is possible for many of the rock groups over much of the ground.
A sedimentological classification of the rocks is not readily accommodated by a usual system of parameters inherited from the classification of detrital terrigenes. Nearly all the limestone endogenic, their calcareous constituents almost never the product of hinterland erosion or prolonged transport even when the 'clasts' within them are abraded fragments. Grain size in such sediments is commonly an accident of origin, not a reliable sign of the restlessness of the environment of deposition; a spirifer shell is much larger than the individual crinoid plates in the bed in which it lies; a stromatolite algal sheet is the welded product of growing algal nodules, and conversely an algal nodule may show partial disintegration into 'amorphouse' algal mud; a coral bush is the enclosing frame of the shells it houses and of the organic debris caught in its mesh, and at the same time it is itself embedded in a bank of the same kind of shells or in the wrappings of the same kinds of debris; drewite mudstone, a faecal pellet, an oolith, reflect related features in carbonate formation.
'Micrite' also has many ambiguities; it may be an accumulate virtually in situ; it may be detritus transported some distance, or fragmented and redistributed locally; it may he mainly of monogenetic provenance, in its shelly or its algal or its evaporitic constituents, and then be coarse-grained or fine-grained, apparently well-sorted, through immediate environmental 'accident', or it may be equally 'accidentally' unsorted or ill-sorted in grain size as an 'internal' product of a mixed biotope; it may be diagenetic, 'contemporaneosu' or 'penecontemporaneous' or 'subsequent'.
In a naive petrographic system mechanically applied, classification can result in the imposition of mutually incommensurable or incompatible criteria in attempts to distinguish between petrological kinds resistant to the system: rocks similar on the arbitary criteria (for instance of grain size) may little mutual affinity; rocks very different on the criteria may be closely allied. Principles in the classification of limestones, as they are illustrated in Avonian rocks need to be self-consistant and comprehensive: they cannot be adequately of use in description unless they are also genetic. [end of abstract].


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Ghummed, M.A. 1982. Petrology and Geochemistry of the Carbonates, Ballagan Formation, N.W. Midland Valley, Scotland. Ph.D. Thesis, Glasgow University, 275 pp. By Dr. Milad Ali Ghummed. University of Glasgow Library. Instantly online as title and abstract only, and from this page the full pdf (18Mb) can be downloaded:
Petrology and Geochemistry of the Carbonates, Ballagan Formation, N.W. Midland Valley, Scotland.
The pdf file is available from the above, free online: pdf-file -
1982MiladPhD.pdf.
Abstract:
This study investigates the nodular and stratified carbonate beds 1n the Ballagan Formation, in the Western Midland Valley of Scotland. The Ballagan Formation, which also includes lutltes and quartz arenites, lies stratigraphically between the Upper Old Red Sandstone end the Spout of Ballagan Sandstone: it constitutes the lower-most part of the Calciferous Sandstone Measures. Microscopic examination of thin sections showed that the carbonates comprise mainly three microfacies which are subdivided on the basis of fabric and crystal-size. Microfacies A is the finest-grained and from it the other two have diagenetically evolved; through neomorphism (Microfacies B), and metasomatism and segregation (Microfacies C). Microfacies B has resulted from multiple neomorphic stages as indicated by crystal-size variation. As a, .result of neomorphism, clay has concentrated In .the intercrystalline boundaries, leaving the new crystals slightly clearer than their precursors. Microfacies C has developed in two ways: (1) metasomatism and (2) segregation. Calcitization of dolomitic beds and segregatIon of calcite in an original argillaceous sediment, both produced Microfacies C. The controlling factors over these processes are unknown. Shrinkage cracks, cavity-cement, and veinlets are common features in both stratified and nodular carbonates. Poorly preserved laminations are uncommon in the untreated rock specimen, but are common in thin section. Whilst it is difficult to prove an algal origin for these structures, they morphologically resemble algal laminations. Calculation of mineral proportions from chemical analyses by X-ray fluorescence show that about 86 percent of the carbonate beds contain more than 50 percent of the mineral dolomite, therefore, they are generally dolomites by definition, with minor limestone occurrences. Terrigeneous material content is composed mainly of clay minerals; illite, chlorite, and montmorillonite with common quartz. Gypsum is a minor lithology in the rock assemblages. Electron microprobe analysis has shown that crystals of both Microfacies A and B are composed mainly of dolomite, the crystals of the first contain more clay than those of the latter. Crystals of Microfacies C are composed of calcite. Probing of veinlets confirmed a wide range of mineral compositions. From a consideration of the fineness, bed-thickness, structures, faunas, composition, rock-association and lateral facies relationships, these beds are thought to have formed in a lagoonal environment. On the seaward the lagoon was probably bounded by sand bars; on the landward by caliche pavements and alluvium. The best analogous environment is seen in the Coorong, 5. Australia, where fine dolomitic beds are laid down during the wet season and desiccated during the dry.
[With good thin-section photomicrographs and much geochemical data. A good work on Carboniferous dolomite of penecontemporaneous origin and associated with evaporites. Relevant to some other Carboniferous dolomites (and also of relevance, beyond the Mendip region discussed here, to the Tweed Borehole Carboniferous research project, re Romer's Gap.)]
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Goodman, S. 1987. The relationship between light hydrocarbons and carbonate petrology - a study from the Mendip Hills. Geological Journal, Volume 22, Issue 4, pages 371 - 382, October/December 1987.
Abstract
Anomalously high values of light hydrocarbons (C1 - C4) have been detected in carbonate rocks hosting base metal mineralization, and have a potential use in mineral exploration. Development of an exploration method based on such anomalies requires an understanding of the controls on the hydrocarbon content of the rocks, other than by mineralization, i.e. the hydrocarbons present in background areas. This study uses gas chromatography to investigate the light hydrocarbons present in rocks from such a background area, the Carboniferous Limestone of the Mendip Hills, in order to determine the extent to which different carbonate lithologies affect the quantity and nature of hydrocarbons present. It appears that the lithological effects are minimal when compared to the anomalous values from mineralized areas. The limited effects are due to variations in the depositional and diagenetic regimes of the original sediments.


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Green , G.W. and Welch, F.B.A. 1964. The Geology of the Country around Wells and Cheddar. Memoirs of the Geological Survey of Great Britain, No. 280. (Explanation of One-Inch Geological Sheet 280, New Series). With contributions by G.A. Kellaway, D.R.A. Ponsford, M. Brooks, and M. Mitchell. Department of Scientific and Industrial Research, London, Her Majesty's Stationery Office. 225pp.

Green, G.W. 1992. British Regional Geology: Bristol and Gloucester Region. Third Edition, based on previous editions by G.A. Kellaway, F.B.A. Welch and R. Crookall. London, Her Majesty's Stationery Office. 188 pp. [a good edition, larger than most British Regional Geology books; this is more in the style of a memoir of the BGS].


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Gregg, J.M., Shelton, K.L., Johnson, A.W., Somerville, I.D. and Wright, W.R. 2001. Dolomitization of the Waulsortian Limestone (Lower Carboniferous) in the Irish Midlands. Sedimentology, vol. 48, Issue 4, pp. 745-766. By Jay M. Gregg, Kevin L. Shelton, Aaron W. Johnson, Ian D. Somerville and Wayne R. Wright.
Abstract:
The Waulsortian Limestone (Lower Carboniferous) of the southern Irish Midlands is dolomitized pervasively over a much larger region than previous studies have documented. This study indicates a complex, multistage, multiple fluid history for regional dolomitization. Partially and completely dolomitized sections of Waulsortian Limestones are characterized by finely crystalline (0.01 - 0.3 mm) planar dolomite. Planar replacive dolomite is commonly followed by coarse ( = 0.5 mm) nonplanar replacive dolomite, and pervasive void-filling saddle dolomite cement is frequently associated with Zn -Pb mineralization. Planar dolomite has average d 18O and d 13C values (parts per thousand PDB) of -4.8 and 3.9 respectively. These are lower oxygen and slightly higher carbon isotope values than averages for marine limestones in the Waulsortian (d 18 O = - 2.2, d 13C = 3.7). Mean C and O isotope values of planar replacive dolomite are also distinct from those of nonplanar and saddle dolomite cement (- 7.0 and 33; -7.4 and 2.4 respectively). Fluid inclusions indicate a complex history involving at least three chemically and thermally distinct fluids during dolomite cementation. The petrography and geochemistry of planar dolomites are consistent with an early diagenetic origin, possibly in equilibrium with modified Carboniferous sea water. Where the Waulsortian was exposed to hydrothermal fluids (70 - 280 degrees C), planar dolomite underwent a neomorphic recrystallization to a coarser crystalline, planar and nonplanar dolomite characterized by lower d 18 O values. Void-filling dolomite cement is isotopically similar to nonplanar, replacive dolomite and reflects a similar origin from hydrothermal fluids. This history of multiple stages of dolomitization is significantly more complex than earlier models proposed for the Irish Midlands and provides a framework upon which to test competing models of regional vs. localized fluid flow.

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Hancock , N.J. 1982. Stratigraphy, palaeogeography and structure of the East Mendips Silurian inlier. Proceedings of the Geologists' Association, London, vol. 93 (3), 247-261.
Abstract: Sedimentary way-up criteria in the 'Wenlock shales' of the East Mendips inlier show that these beds, previously believed to overlie Silurian andesitic lavas and tuffs unconformably, are inverted and underlie the volcanics, probably conformably. A regressive sequence of brachiopod communities occurs in the shale and overlying tuffs. This regression is dated as probably M. riccartonensis zone (Lower Wenlock) by Eocoelia angelina, suggesting that the volcanics are also Wenlock. The regression is not contemporaneous with the widespread late Wenlock shallowing of Wales and the Welsh Borderland, and is probably related to the volcanism. Remapping of the inlier shows that although the Silurian beds are situated in the core of the East Mendips anticline, they exhibit no anticlinal structure within themselves. This, taken together with the discrepant Old Red Sandstone thicknesses north and south of the inlier, demonstrates that the southern boundary of Silurian rocks constitutes and overthrust and not an angular unconformity as hitherto believed. An exposed volcanic neck forms one possible source for the numerous Wenlock bentonites in Wales and the Welsh Borderland.
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Hitzman, M.W., Allan J.R. and Beaty, D.W., 1998. Regional dolomitization of the Waulsortian limestone in southeastern Ireland: evidence of large scale fluid flow driven by the Hercynian orogeny. Geology, 26, 547-550.
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Harrison, D.J., Buckley, D.K. and Marks, R.J. 1992. Limestone Resources and Hydrogeology of the Mendip Hills. British Geological Survey, Keyworth, Nottingham, Technical Report, WA/92/19.
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Hobbs, S.L. 1988. Recharge, Flow and Storage in the Unsaturated Zone of the Mendip Limestone Aquifer. Unpublished Ph.D. Thesis, University of Bristol. [not seen].
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Hopson, C. A and Melson, W.G. 1990. Compositional Trends and Eruptive Cycles at Mount St. Helens. Geoscience Canada, vol. 17, no. 3, pp. 131-141. By Clifford A. Hopson, William G. Melson
Available online as a pdf file:
Hopson and Melson, Compositional Trends and Eruptive Cycles at Mount St. Helens.
Abstract
The 40,000-year eruptive history of Mount St. Helens reveals an overall compositional trend from rhyodacite to andesite, with basalt at ~1.9 and ~1.6 ka. A cyclic eruption pattern is superimposed on this trend. Cycles comprised a repose interval, when compositional and thermal gradients developed in the underlying magma body, followed by an eruption interval in which progressive tapping of magma beheaded these gradients. Recovery of gradients varied with duration of the ensuing repose period. Eruption sequences follow the pattern: (1) eruptive progression from Plinian eruptions to dome growth accompanied by pyroclastic flows and tephra, followed (in some cases) by lava flows punctuated by pyroclastic outbursts; (2) a mineralogic progression from hydrous Fe-Mg phenocrysts (hb, cm, bi) toward pyroxenes; (3) a magmatic compositional progression from rhyodacite or dacite to andesite. Progressions 1 and 2 stem mainly from volatile gradients in the magma reservoir whereas progression 3 (and to some extent 2) reflects gradients of melt composition and crystal content. Three eruption cycles within the last 4,000 years follow this pattern. Earlier cycles are probable but only dimly perceived, mainly from the partial record of tephras and pyroclastic flows.
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Lewis, D.N., Donovan, S.K. and Sawford, P. 2003. Fossil echinoderms from the Carboniferous Limestone sea defence blocks at Barton-on-Sea, Hampshire, southern England. Proceedings of the Geologists' Association , 114, 307-317.
Abstract: The sea defence/coastal protection works at Barton-on-Sea, Hampshire include blocks of Carboniferous Limestone (Clifton Down Limestone Formation, Dinantian, Holkerian) from the Foster Yeoman 'Torr Works' Quarry at Merehead, East Cranmore, Shepton Mallet, Somerset. A rich fauna of echinoderms, corals, bryozoans, trilobites, brachiopods and gastropods is present in these blocks. The echinoderms include plates of the tests of the echinoids Palaechinus sp., Archaeocidaris sp. and an indeterminate echinoid: calyces of the crinoids platycrinitid sp., Actinocrinus sp. aff. A. rotundatus Wright, monobathrid sp. indet., camerate sp. indet. and Taxocrinus sp.; and numerous ossicles, including Cyclothyris (col.) sp. and Pentagonocyclicus (col.) spp. Camerates were important members of early Carboniferous crinoid faunas, although the absence of cladids is notable. Examination of any fossils contained within coastal protection blocks is an important source of information when the place of origin of the blocks is known but is unavailable for study purposes. [by David N. Lewis, Natural History Museum, London, Stephen K. Donovan, Nationaal Natuurhistorisch Museum, Leiden, and Paul Sawford, Ruislip Road, Northolt, Middlesex.]
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Llewellyn , P.G. and Stabbins, R. 1970. The Hathern Anhydrite Series, Lower Carboniferous, Leicestershire, England, Institute of Mining and Mineralogy, 79 (1970), pp. B1-B15.
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Nagy , Z.R., Somerville, I.D., Gregg, J.M, Becker, S.D. and Shelton, K.L. 2005. Lower Carboniferous peritidal carbonates and associated evaporites adjacent to the Leinster Massif, southeast Irish Midlands. Geological Journal, vol. 40, Issue 2, pp. 173-192. By Zsolt R. Nagy, Ian D. Somerville, Jay M. Gregg, Stephen P. Becker, and Kevin L. Shelton.
Abstract
Analysis of a 275 m-thick section in the Milford Borehole, GSI-91-25, from County Carlow, Ireland, has revealed an unusual sequence of shallow subtidal, peritidal and sabkha facies in rocks of mid?-late Chadian to late Holkerian (Viséan, Lower Carboniferous) age. Sedimentation occurred on an inner ramp setting, adjacent to the Leinster Massif. The lower part of the sequence (late Chadian age) above the basal subtidal bioclastic unit is dominated by oolite sand facies associations. These include a lower regressive dolomitized, oolitic peloidal mobile shoal, and an upper, probably transgressive, backshoal oolite sand. A 68 m-thick, well-developed peritidal sequence is present between the oolitic intervals. These rocks consist of alternating stromatolitic fenestral mudstone, dolomite and organic shale, with evaporite pseudomorphs and subaerial exposure horizons containing pedogenic features. In the succeeding Arundian–Holkerian strata, transgressive–regressive carbonate units are recognized. These comprise high-energy, backshoal subtidal cycles of argillaceous skeletal packstones, bioclastic grainstones with minor oolites and algal wackestones to grainstones and infrequent algal stromatolite horizons.
The study recognizes for the first time the peritidal and sabkha deposits in Chadian rocks adjacent to the Leinster Massif in the eastern Irish Midlands. These strata appear to be coeval with similar evaporite-bearing rocks in County Wexford that are developed on the southern margin of this landmass, and similar depositional facies exist further to the east in the South Wales Platform, south of St. George's Land, and in Belgium, south of the Brabant Massif.
The presence of evaporites in the peritidal facies suggests that dense brines may have formed adjacent to the Leinster Massif. These fluids may have been involved in regional dolomitization of Chadian and possibly underlying Courceyan strata. They may also have been a source of high salinity fluids associated with nearby base-metal sulphide deposits.
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Pickering, A. [Andrew Pickering] and Foster, N. [Nicola Foster]. Cheddar through Time. Book. (also E-book available through Amazon for 4 pounds, 99 pence.) Paperback, by Andrew Pickering and Nicola Foster. 31st August 2011.
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Ponsford, D.R.A. 1970. Silurian volcanic rocks of the Mendip Hills, Somerset. Geological Magazine, vol. .
Available online: Ponsford, 1970, Silurian volcanic rocks.
The recent paper by Dr. P.C. van de Kamp on the above topic (Geol. Mag., 106, 1969, 542-553) is of considerable interest. The author claims that the main rock is rhyodacite whereas all previous publications and our own researches have suggested that the main lava flows are of andesitic composition. The main reason for the new opinion would seem to be aa high quartz content in the rocks based on chemical analyses and it is pertinent to enquire whether this could be due to secondary enrichment.
[.. continues ...]
A further interesting point in connection with the Silurian volcanic rocks of the Mendips concerns the origin of the rounded lava masses found in the tuff beds and referred to by Dr van de Kemp as "abundant bombs in ash matrix". Since their first discovery by Reynolds (1907) they have been called conglomerates but I agree that they should be termed agglomerates. However, like Reynolds, I could not accept that they are bombs and could offer no alternative until a a recent paper by Dr Doris Reynolds (1969) which has supplied, in my opinion, the true explanation, namely gas-fluidization whereby tuff fragments, moved by gas under pressure, becomes an erosive agent in the volcanic vent. The agglomerate was reported to occur in strength 0.8Km. (half a mile) east of Moons Hill and interpreted by Reynolds (1907) as marking the site of a vent. His ideas would now seem to be confirmed but many details remain to be resolved. [references follow]
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Reynolds , Sidney H. 1907. A Silurian inlier in the eastern Mendips. Quarterly Journal of the Geological Society, London, Vol. 63, pp. 217-240. By Professor Sidney Hugh Reynolds, M.A. F.G.S. Read March 13th 1907.
The Mendip Hills consist of four periclinal upfolds of Carboniferous Limestone, arranged en echelon from north-west to south-east. Each pericline includes a core of Old Red Sandstone [Devonian], and the igneous rocks. It is with these that the present paper deals. The existence of igneous rocks in the Eastern Mendips was first noted by Charles Moore [Quarterly Journal of the Geological Society, 1867, vol. 23.] who described them as:
"a basaltic dyke of considerable thickness emerging from the beneath the Old Red Sandstone at East End near Stoke Lane" [the rocks are actually of andesite not basalt]
He considered that, from the general physical character of the Mendips, it was not improbable that the dyke might be co-extensive with their range. He not only attributed the upheaval of whole Mendip range to the intrusion of this igneous mass, but also considered that it was responsible for the remarkable inverted character of the Carboniferous beds at Luckington, where the Coal-Measures are worked under the Carboniferous Limestone.
John Morris refers to the rock at Stoke Lane, as
"a dyke of considerable thickness, emerging from beneath the Old Red Sandstone, occurring as bosses in the field, but, traced for some distance over the district, it is conglomeratic in places, and pronounced by Mr. D. Forbes to be dolerite"
The igneous rocks are not shown in Sander's map of the Bristol Coalfield (published in 1864), but appear in the map of the Geological Survey (1884), as a series of isolated patches extending from Downhead on the east to Beacon Plantation, southwest of Stoke Lane, on the west, a distance of about 3 miles. [....continues].

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Reynolds, Doris L. 1954. Fluidization as a geological process, and its bearing on the problem of intrusive granites, American Journal of Science, 252 (1954), pp. 577-613. By Dr. Doris Reynolds.

Reynolds, Doris L. 1969. Fluidization as a volcanological agent. Proceedings of the Geological Society, London, No. 1655, pp. 110-115.


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Simms, M.J. 1990. Triassic palaeokarst in Britain. Cave Science, vol. 17, No. 3, December 1990. Transactions of the British Cave Research Association. Available online as a pdf file. See the section on the Mendip Hills, p. 95 et seq.

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Somerset Historic Environment Record 10397. Great Oone's Hole, Cheddar Gorge, Cheddar.
An open hole, 300ft above the road. On the left bank of Cheddar Gorge 80m above the present valley floor and 15m below the plateau. A 4m wide entrance leads into a roomy tunnel c.150m long. Outside the entrance is a 5m wide platform.
(Ransacked, with no record of finds. However, there are finds in Weston-super-Mare museum which may have come from this site, including Upper Palaeolithic flints. There are fake paintings in this cave. Davies claims Upper Palaeolithic finds; Campbell accepts two pieces as possible. Partial excavations c.1902 and 1970s revealed Later Upper Palaeolithic flint artefacts and faunal material.)


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Dr. William Stanton, hydrogeologist, speleologist and specialist on the caves of Mendip. He published various books and papers on the subject of Mendip caves and on other matters. See also Barrington. (Barrington, N. and Stanton, W. 1977. Mendip: The Complete Caves and a View of the Hills. Cheddar Valley Press. Paperback.). The late Dr Stanton was awarded his doctorate in geology and spent his career working in hydrogeology throughout the world including many parts of Africa and Portugal. He returned to Westbury-sub-Mendip upon his retirement where he was instrumental in local projects involving caving and wildlife and won an MBE in 1993. He and his wife died in 2009-2010 in sad circumstances (press reports online).

Stanton, W.I. (date?) Cheddar Caves. Book, published by Photo Precision Ltd. Paperback.

Stanton, W.I. 1977. Mendip Water. In Barrington, N. and Stanton, W.I. (Eds.) Mendip: The Complete Caves and a View of the Hills. Cheddar Valley Press, Cheddar, pp. 201-213.

Stanton, W.I. 1985. Cheddar Gorge and Gough's Cave. Proceedings of the University of Bristol Spelaeological Society, vol. 17, part 2, pp. 121-128. By Dr. W.I Stanton.
This paper is available online as a pdf file. Find by Google or other search engine - "Cheddar Gorge and Gough's Cave - UBSS" or search for "Stanton Mendip Cheddar Gorge" or for "Stanton Mendip UBSS".
[an aerial photograph by Aerofilms is shown at the start]
[Introductory text follows as an example. See particularly the figures which contain plans and section through the cave systems.]
"Cheddar Gorge is the classic example of a waterless limestone gorge with a tributary sysem of waterless limestone valleys. It is also one of Britain's greatest natural scenic attractions. Opening into it are several caves at different levels, whose origins are linked to the development of the gorge. The largest known cave is Gough's Cave, visited by half a million tourists each year. The Origin of Cheddar Gorge. Early speculation on the origin of Cheddar Gorge ranged from earthquake riftine to marine erosion. These ideas were replaced in the later nineteenth century by the cavern collapse hypothesis (Winwood and Woodward, 1891) which held that the "Cheddar Pass" had been created by roof collapse in a series of great caves. Balch (1947, pp. 65-7) summarized the arguments for collapse, citing the approach ravine to Wookey Hole Cave as an example of the process in action. Present day views on dry valley formation were heralded by Reynodls (1927) who argued that the smaller dry limestone gorge of Burrington Coombe, 4 km north of Cheddar, was eroded by a surface stream. This was possible because the ground was permanently frozen in the colder phases of the Pleistocene. Water from rain or snowmelt could not infiltrate underground as it does now, but ran off the Mendip plateau via the existing river system, eroding gorges where the flow was strong and the gradient steep. Coleman and Balchin (1960) introduced a different concept, regarding 'Cheddar Gorge as a simple youthful valley which has recently performed the typical youthful action of abandoning its surface course for an underground one'. Ford and Stanton (1969) combined earlier theories by arguing that Mendip dry valleys and gorges were excavated in two main stages. First when sea level was higher and the Mendips were hardly distinguishable as a range of hills the high water table in the limestone allowed permanent surface drainage in the principal valleys, as happens today in the far east of Mendip in, for example, the Nunney Brook. Later when sea level fell during the Early Pleistocene and the Mendips were rapidly exhumed from their enveloping soft post-Carboniferous strata, the water table dropped faster thatn the streams could wear down their beds. Swallets and caves formed, and the surface flow in the valleys became intermittent, finally ceasing except in great floods. In periglacial phases of the Pleistocene the ground froze, the swallets and percolation channels were blocked with ice and frozen mud, and summer meltwater torents reactivated the valley systems. The steepest gradients were at the valley mouth, which had been left 'hanging' by the exhumation process, and there the gorges developed. Cheddar Gorge, with its catchment area of 40 square kilometres (most of the Mendip Plateau), is by far the biggest. The smaller gorges, Ebbor and Burrington, have catchment areas of only about 3 square kilometres each.
[continues: with "Morphology of Cheddar Gorge" etc.]

Stanton, W.I. 1988. The Ancient Springs, Streams and Underground Watercourses of the City of Wells. Wiltshire Natural History and Archaeological Society. Annual Reports for 1987 and 1988, pp. 25-46. By the late Dr. W.I. Stanton. [Further information. This article has been extracted from pages 25-48 of the ninety-ninth and one hundredth Annual Reports for 1987 and 1988 to commemorate the centenary of the Wiltshire Natural History and Archaeological Society. Wells Museum, 8 Cathedral Green, Wells, Somerset, BA5 2UE. It includes a map showing 11 swallet holes connecting to St. Andrew's Well, Wells. The publication has not been seen by the present writer but it may be a booklet obtainable from the museum.]

Stanton, W.I. 1991. Hydrogeology of the Hot Springs of Bath. In Kellaway, G.A. (ed.). Hot Springs of Bath. Bath City Council, Bath, pp. 127-142.


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Stow , D.A.V. 2005. Sedimentary Rocks in the Field: A Colour Guide. By Dorrik A.V. Stow. Manson Publishing, 320pp. [This is an excellent book with numerous clear colour photographs, and is superb for recognition of sedimentary rock types and sedimentary structures.]
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Van De Kemp, P.C. The Silurian rocks of the Mendip Hills, Somerset; and the Tortworth area, Gloucestershire, England. Geological Magazine, Vol. 106, No. 6, 1969, pp. 542-553, plates 28-29.
Available online:
Van de Kemp, 1969. Silurian rocks of the Mendip Hills.
Abstract:
Field, petrograph and chemical studies on the Silurian volcanic rocks of the Mendip Hills show that there are probably 15 or more rock units in the series including andesite and rhyodacite lavas, rhyodacite tuffs, agglomerates, and a dolerite dyke. The predominant rock type is rhyodacite which may be as much as 80 percent of the volcanics. Volcanics of Silurian age from the Tortworth area, Gloucestershire, are of latite-andesite composition.
The Mendip rocks have been deuterically altered. Calcite-quartz-laumonite veins are common in fractures in these rocks. The agglomerates are particularly susceptible to weathering and some bombs are extensively altered to clays. Twelve rocks were chemically analysed for 36 elements each. no anomalous base metal concentrations were found in the volcanics although Pb, Zn, and Cu mineralisation is known in the are. K/Rb varies from 202 to 909 in these calc-alkaline rocks.
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Wainwright (a company supplying aggregrate). 2008. Geology: Moons Hill and Stoke Quarries. Go to website: Wainwright: Geology: Moons Hill and Stoke Quarries.
Example extract follows, but see the full website with photographs.
The rocks extracted from Moons Hill and Stoke Quarries are volcanic in origin and were formed 425 million years ago during the Silurian period of geological time. They form part of a renowned feature of British geological history and have been the subject of much debate and research over the years. The volcanoes which produced the lavas, ashes and other rock types extended over a wide area of what is now south west England. Rocks of the same type and age can be found in Devon and Gloucestershire.
Volcanic lavas, described as Andesites, were extruded over a wide area forming beds up to 100 to 150 metres deep. During this period of volcanic activity, accumulations of volcanic ash also built up, sometimes overlying the lavas, sometimes interbedded with them. The fine-grained ashes are known as Tuffs and often contain blocks or cobbles of Andesite lavas; these formations are known as Agglomerates. Because of the presence of shale and mudstone below the volcanic rocks and sometimes interbedded with them, we know that this volcanic activity was taking place in a marine environment. The whole sequence of lavas, ashes and agglomerates can be readily identified and measured in the Quarry because the beds are now standing vertically on end like books on a bookshelf.
After being deposited in a semi-molten state in horizontal layers, the volcanic rocks cooled and solidified and were eventually buried by thousands of metres of sedimentary rocks including terrestrial sandstones and limestones formed in oceans and lagoons. Many millions of years later these rock beds were subjected to an intense period of structural uplift resulting in the formation of the Mendip anticlinal folds, in the core of which the most ancient formations can be found. The idealised cross section through Moon's Hill quarry shows how the volcanic rocks now lie in relation to the other formations.
At Moons Hill and Stoke Quarries we concentrate on producing aggregate from the Andesite beds, these being generally stronger and more durable than the Tuffs. The latter are however quite suitable for most specifications. The Andesite aggregates are regarded as roadstone of the highest quality.
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Wall , G.R.T. and Jenkyns, H.C. 2004. The age, origin and tectonic significance of Mesozoic sediment-filled fissures in the Mendip Hills (SW England): implications for extension models and Jurassic sea-level curve. Geological Magazine, July 2004, vol. 141, no. 4, pp. 471-504.
Abstract:
In the eastern Mendip Hills, on the northern margin of the Wessex Basin, SW England, the Carboniferous Limestone is cut by numerous fissures that are filled with Mesozoic sediments (sedimentary dykes, neptunian dykes). The fissures contain a record of Triassic-Lower Jurassic sediments that are only sparingly preserved in their normal stratigraphical position between the Carboniferous Limestone and the unconformably overlying Upper Inferior Oolite of Bajocian age. Detailed analysis of cross-cutting relationships, facies analysis, biostratigraphy, lithostratigraphy and strontium-isotope ages of relevant Mesozoic sediments has allowed the construction of an Upper Triassic-Lower Jurassic fissure-fill stratigraphy for the eastern Mendip area. Most fissures were clearly formed by rapid influx of unlithified sediment from the land surface or sea floor. Some smaller cavities, or larger cavities with restricted access to the unconformity, were apparently filled by sediment that trickled down into the fissure system. The vast majority of the Mendip fissures are interpreted as having formed as a response of the Carboniferous Limestone, north of major basin-bounding faults, to pulses of tectonic extension during Ladinian-Norian/Rhaetian, late Hettangian-early Sinemurian, late Sinemurian-early Pliensbachian, mid-Pliensbachian, late Pliensbachian and Bajocian times. Triassic-earliest Jurassic fissures have a broad spread of strike from E-W to NW-SE to N-S, accommodating extension in a roughly NE-SW direction. Younger Jurassic fissures show well-defined E-W and N-S trends with the former becoming dominant through time. Total extension of about 4.7 percent N-S and about 0.6 percent E-W was produced by the formation of Triassic-Jurassic fissures within the Carboniferous Limestone. Such patterns of extension are thought likely to be characteristic of the subsurface geology in much of southern England and Wales. Major implications of this study are that: (1) the presence of seismically unresolvable sediment-filled fissures in supposedly rigid fault blocks can lead to a significant underestimate of regional extension based on the restoration of motion on normal faults on seismic-reflection profiles, and (2) the isolation of pulses of tectonic activity with a temporal resolution of 105-106 years may provide a means of identifying a tectonic signal in relative sea-level curves derived from the Jurassic sedimentary record.
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Welch , F.B.A. 1929. The geological structure of the central Mendips. Quarterly Journal of the Geological Society, London, vol. 85, issue 1-4, pp. 45-76. Extract: "The area here termed the Central Mendips comprises that part of the Mendip Hills which lies between Cheddar and Shepton Mallet. This paper deals only with the Palaeozoic rocks, which occupy the greater part of the area, and appear in inliers among the Mesozoic rocks on the south."
Available online as a pdf from the Lyell Collection of the Geological Society, London.

Welch, F.B.A. 1933 (for 1932). Geological structure of the eastern Mendips. Quarterly Journal of the Geological Society, London, vol. 89 for 1932, pp. 14 - 52. Accessible as a pdf file from the Geological Society Lyell Collection. By Francis Brian Awburn Welch.
No abstract. Example extract from Introduction:
Geologically, the area consists of the Beacon Hill pericline, which is the most southerly situated of the four echeloned periclines constituting the Mendip Hills. This pericline forms an approximately east-and-west ridge which attains at its western end a maximum altitude of 974 feet O.D. Its ridgelike character, especially prominent in its western part, is due to the resistant nature of the rocks of which it is composed: namely, Carboniferous Limestone, 'Millstone Grit,' and a central core of Old Red Sandstone and Silurian rocks. Succeeding these hard beds on the north are the soft Coal Measure shales (Lower Coal Measures), whilst the low ground on the south is occupied by Mesozoic strata banked against the Palaeozoic massif.


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West , I.M., Brandon, A. and Smith, M. 1968. A tidal flat evaporitic facies in the Visean of Ireland. Journal of Sedimentary Petrology, vol. 38, No. 4, pp. 1079-1093, Figs 1- 14, December 1968. By Ian M. West, Alan Brandon and Melvyn Smith, Department of Geology, The University of Southampton, England.

A slightly revised version of this paper is available as a webpage of this website. Please go to:

West, Brandon and Smith. A tidal flat evaporitic facies in the Visean of Ireland. (revised version online, 2010).

(To see a rather poor copy of the original, unrevised paper go to:
Appendix - Carboniferous Evaporites - Ireland - West, Brandon and Smith.)

Abstract:
A sequence of thinly bedded limestones, dolomites, shales and sandstones contains evaporitic beds in County Leitrim and Cavan, Republic of Ireland. This sequence constitutes the Aghagrania Formation (new name) of B2 to PIc age, (Upper Visean), with a type section east of Drumshanbo, County Leitrim. The evaporitic beds which have not previously been recorded from this horizon or locality, are mostly unfossiliferous laminated limestones and dolomites with macrocells [nodules of the usual calcium sulphate type, i.e. chickenwire] and with pseudomorphs after gypsum, anhydrite, and halite. This facies of the Aghagrania Formation also includes evaporitic breccias, and celestite and carbonate replacements of calcium sulphate. Blocks of gypsum in boulder clay, on the shore of Lough Allen, are probably derived from these beds. The evaporitic strata alternate with shales and limestones containing marine faunas, and with unfossiliferous sandstones. All the facies show evidence of shallow water deposition and were probably formed in an area of low relief subjected to transgressions and regressions of a shallow sea. The evaporitic beds may be compared to the dolomite and gypsum deposits of present day tidal flats and associated shallow lagoons. They also resemble certain other occurrences of ancient laminated dolomite and limestone beds which been recently described and attributed to a tidal flat origin.


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Whittaker, A. and Green G.W. 1983. Geology of the Country around Weston-super-Mare. Memoirs of the Geological Survey of Great Britain, H.M.S.O. London.
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Williams, G.D. and Chapman, T.J. 1986. The Bristol-Mendip foreland thrust belt. Journal of the Geological Society, London, vol. 143, pp. 63-73.
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Wood, M.W. and Shaw, H.F. 1976. The geochemistry of celestites from the the Yate area near Bristol (U.K.). Chemical Geology, vol. 17, pp. 179-193.


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Wright, V., Woodcock, N.H. and Dickson, J.A.D. 2009. Fissure fills along faults: Variscan examples from Gower, South Wales. Geological Magazine. Volume 146, Issue 06, November 2009, pp 890-902.
Abstract:
The extent to which persistent, rather than transient, fissures (wide planar voids) can exist along upper crustal faults is important in assessing fault permeability to mineral and hydrocarbon-bearing fluids. Variscan (late Carboniferous) faults cutting Dinantian (Lower Carboniferous) limestones on the Gower peninsula, South Wales, host clear evidence for fissures up to several metres wide. Evidence includes dendritic hematite growth and elongate calcite growth into open voids, spar ball and cockade breccia formation, laminated sediment infill and void-collapse breccias. Detailed mapping reveals cross-cutting geometries and brecciation of earlier fissure fills, showing that fissures were formed during, rather than after, active faulting. Fissures therefore probably formed by geometric mismatch between displaced fault walls, rather than by solution widening along inactive faults.

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Copyright © 2015 Ian West, Catherine West, Tonya Loades and Joanna Bentley. All rights reserved. This is a purely academic website and images and text may not be copied for publication or for use on other webpages or for any commercial activity. A reasonable number of images and some text may be used for non-commercial academic purposes, including field trip handouts, lectures, student projects, dissertations etc, providing source is acknowledged.

Disclaimer: Geological fieldwork involves some level of risk, which can be reduced by knowledge, experience and appropriate safety precautions. Persons undertaking field work should assess the risk, as far as possible, in accordance with weather, conditions on the day and the type of persons involved. In providing field guides on the Internet no person is advised here to undertake geological field work in any way that might involve them in unreasonable risk from cliffs, ledges, rocks, sea, caves, unstable quarry faces or other causes. This web page is not a caving guide and it does not recommend entry into any caves, other than commercial show caves. Individuals or group leader should take suitable observations and precautions regarding risk from road traffic, particularly in Cheddar Gorge, and industrial traffic in quarries. Not all places discussed in this website need be visited and the descriptions and photographs here can be used as an alternative to visiting. Individuals and leaders should take appropriate safety precautions, and in bad conditions be prepared to cancell part or all of the field trip if necessary. Permission should be sought for entry into private land and no damage should take place. Attention should be paid to weather warnings, local warnings and danger signs. No liability for death, injury, damage to, or loss of property in connection with a field trip is accepted by providing these websites of geological information. Discussion of geological and geomorphological features, coast erosion, coastal retreat, storm surges etc are given here for academic and educational purposes only. They are not intended for assessment of risk to property or to life. No liability is accepted if this website is used beyond its academic purposes in attempting to determine measures of risk to life or property.

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Dr Ian West, author of these webpages

Webpage - written and produced by:


Ian West, M.Sc. Ph.D. F.G.S.

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at his private address, Romsey, Hampshire, kindly supported by Southampton University,and web-hosted by courtesy of iSolutions of Southampton University. The website does not necessarily represent the views of Southampton University. The website is written privately from home in Romsey, unfunded and with no staff other than the author, but generously and freely published by Southampton University. Field trips shown in photographs do not necessarily have any connection with Southampton University and may have been private or have been run by various organisations.