Sheffield

THE GEOLOGY OF THE BUILDING AND DECORATIVE STONES OF CORNWALL - SUPPLEMENTARY PUBLICATION

Granites and Elvans

Colin Bristow

THE GRANITES

The granite quarrying areas are here described in greater detail than in the published paper, starting in the west and working eastwards towards the Tamar.

Land’s End granite

Apart from the Isles of Scilly granite, this is the most westerly of the Cornish granites, and also one of the youngest granites, having been intruded during the period 275-280 million years ago in the early part of the Permian Period (Darbyshire & Shepherd 1985; Chesley et al. 1993; Chen et al. 1993; Clark et al. 1993). It has also been suggested that the granite is really two separate intrusions, with the earliest intrusion dated at 278 million years old forming the Zennor Lobe in the northeast, and the St Buryan lobe in the southwest dated at 275 million years old, which is partly covered, on its western side, by the waters of the Atlantic Ocean. Both lobes of the granite are clearly composite, with a large area of fine grained granite around Castle-an-Dinas in the Zennor lobe and a number of smaller patches of fine grained granite in the St Buryan lobe. The contact between the granite and the rocks of the metamorphic aureole (mostly hornfels and metabasics) is superbly displayed along the north coast of the Penwith peninsula.

There has been extensive quarrying of this granite mass, although not on the same scale as in the Carnmenellis and Bodmin Moor granites. This may be due to the more difficult transport logistics from the quarry to the port and some concerns about the quality of the granite in some of the quarries. The Land’s End granite is of a different type to the more intensively worked quarries further east in Cornwall and Devon and this may also have some bearing on its quality. However, it may simply be that quarrying in the Land’s End granite was never on a sufficiently large scale to reach the really sound granite at depth. In spite of this much Land’s End granite was exported and used in major structures outside Cornwall.

Probably the most important quarries for building stone were at Lamorna Cove. The quarries are high on the hillside northeast of the Cove (SW452/243 and SW451/244); large blocks of discarded slightly weathered and unsound granite still form a prominent feature below these quarries. Most of these blocks represent slightly decomposed granite which had to be removed in order to get at the sound granite below. This is a coarse grained porphyritic granite with large orthoclase phenocrysts randomly oriented, which meant that the granite was very tough with no pronounced direction of splitting. This feature also made working the granite more difficult. Fresh Lamorna granite is grey with white orthoclase phenocrysts which show zoned inclusions. The granite also contained many xenoliths composed of cordierite and biotite. These were thought by the quarrymen to spoil the appearance of the granite. A small quarry on the west side of the cove (SW450/239) is said to have yielded poorer quality granite.

The small harbour and pier at Lamorna were used for some shipments, with the blocks being manhandled with chains to drag them down to the small harbour. A large block can still be seen beside the harbour. However, the size of ship was very restricted and the harbour not well protected from storms. Larger shipments, particularly for export, had to be taken to Penzance. There is a famous painting by Stanhope Forbes, one of the Newlyn School of artists, of a wagon carrying a block of granite, going down Paul Hill towards Penzance.

Mitchell (1977) reported that Lamorna granite was used in the building of the Embankment in London, the new pier at Mousehole, the Wolf Rock lighthouse, the base of Sir Humphry Davy’s monument in Penzance and for the steps in front of St John’s Hall. One of these steps uses a single block of granite eighteen feet long, which is claimed to be the largest piece of granite incorporated into a building in Britain. Local tradition says that the whole of the St John’s Hall building (including the Royal Geological Society of Cornwall wing) was built with Lamorna granite.

In addition Stanier (1999) lists Devonport Dockyard, Portland and Alderney breakwaters, the first Bishop Rock lighthouse, Bank of New Zealand (Moorgate, London), Café Monico (Piccadilly), Lloyd’s Bank (Lombard St.), New Scotland Yard (the old one) as buildings which have used some Lamorna granite. The quarries ceased operation in 1912.

About one kilometre north-north-west of the Lamorna quarries is the Castallack group of quarries (SW447/253), which saw quarrying activity up to the mid-1980s. Most of the granite was used for monumental purposes.

Halfway between Lamorna and Penzance is Sheffield quarry (SW454/268) which exploited a coarse-grained granite with phenocrysts of feldspar lying in one direction, thus accentuating the ‘bedding’ in the quarry. Worked up until the late 1920s, it had the reputation of being a good quality granite. The Penzance war memorial was constructed from this granite.

New Mill quarry (SW459/342) exploited a coarse-grained granite about 4 kilometres north of Penzance, but had ceased operating by the First World War. It is reputed to have much used for dock work (Reid & Flett 1907).

Small quarries near Zennor and St Just worked coarse-grained granite which was used locally and for housing in Penzance and St Ives. There are many other small quarries in the coarse grained granite which supplied stone for purely local use.

The most important quarry in the fine grained granite is Castle-an-Dinas (SW487/347), situated about 4.5km northeast of Penzance in the middle of the Zennor lobe of the intrusion. This is the only quarry in the Land’s End granite which is still in production, most of the output nowadays is in the form of crushed aggregate, but some walling and hedging stone is also produced. It is sufficiently fine grained to have been called ‘elvan’, ‘freestone’, ‘sandstone’ or ‘whetstone’ in the early days of quarrying, and contains megacrysts of orthoclase feldspar and quartz, with occasionally some biotite megacrysts, set in a fine grained matrix. Initially only the top weathered fifteen feet of granite was quarried, and many buildings in Penzance, Newlyn, Marazion and St Ives used this type of stone. Reid & Flett (1907) reported that it did not split in the same way as the coarse grained granite. Gateposts were never made of this stone, but brought from a distance. Nowadays crushed stone from this quarry is valued for its skid resistance. When used as aggregate in the wearing course of a tarmac road, the best stone tends to come from the deeper levels of the quarry, where the granite is unaltered and grey in colour. The stone for present day building use comes from the upper levels of the quarry where it is a pleasant buff colour. It has been used in the recently constructed leisure centres at St Ives and Penzance, the Minack theatre, Rock lifeboat station and in many private housing developments in Cornwall.

Quarrying on Gulval Downs and Ludgvan Parish quarry at Inch’s Castle also exploited the fine grained granite. Several small quarries in a separate area of fine-grained granite were formerly exploited on the north-north-west side of Knill’s Monument near St. Ives. Patches of coarse-grained granite within the fine-grained granite were reported by Reid & Flett (1907) from this locality, together with much tourmaline.

Worth (1875) mentions a Tregenver granite as being a particularly good building stone (see below) but this locality is not known for certain; De la Beche (1839) mentions a granite at Tregender, near Ludgvan: “a granite composed of felspar, quartz, schorl and an abundance of mica”, this may be the Tregenver locality, but no quarry is now known in the area.

Tregonning – Godolphin granite

This small granite mass contains highly evolved granites similar to the western part of the St Austell pluton. Dating evidence indicates that the intrusion is slightly older than the Land’s End granites, but appreciably younger than the Carnmenellis granite. William Cookworthy made his original discovery of china clay at Tregonning Hill in 1746. Most of this small intrusion is a non-porphyritic lithium-mica granite composed of orthoclase, albite, quartz and a pale brown lithium-bearing mica. Accessory minerals include topaz and tourmaline (Goode & Taylor 1988). A smaller area in the centre of the intrusion is in medium grained biotite granite with small K-feldspar megacrysts. Goode and Taylor believed that the biotite granite formed a sheet overlying the lithium-mica granite. The granite mass is variably kaolinized, there were two china clay works near Tresowes Green in the lower ground, but neither have been active in the last 100 years. Cookworthy’s 1746 discovery is reported to have been at Tregonning Hill, where there is a pit in variably stained and kaolinised granite which appears to have been used later for brick manufacture.

The lithium-mica granite resembles St Stephen’s Stone from the St Austell granite and appears to have enjoyed an excellent reputation as a building stone, because it is attractive in appearance and easy to work. Borlase (1758) notes that Tregonning was one of the most attractive granites to be worked in Cornwall, he says that white Tregonning “is the tenderest and freest kind of this stone and neatest for mouldings”, and is even more enthusiastic about yellow Tregonning “this is a very beautiful stone, works as well as the white Tregonin before-mentioned, and is therefore reckoned among our best granites”. Worth (1875) says that most of the granite used in the Churches of the Land’s End district of West Cornwall used either Tregonning or Tregenver, although he says the latter stone is now exhausted. He also says Godolphin House (Listed Grade 1) and Helston Parish Church were both constructed from Tregonning granite, both probably in the form of moorstone.

There are two quarries on either side of Tregonning Hill, the one on the west side is Gluyas quarry (SW603292) and Tolmennor quarry is on the east side (SW607/294). Both quarries are in the lithium-mica granite. Stanier (1999) reports that some stone was exported for use in Plymouth breakwater and Keyham dockyard. Gluyas closed just before the First World War and Tolmennor closed just before the Second World War.

No quarrying of significance has been reported in the granite forming the southern half of St Michael’s Mount.

Carnmenellis (including Carn Brea, Carn Marth, St Agnes and Cligga)

The Carnmenellis granite is one of the older granites, intruded 295-290 million years ago. It is entirely a biotite-muscovite granite (Fig. 10 – in main paper) and is similar to the Bodmin Moor granite, which is slightly younger. It hosted the greatest concentration of granite quarrying in Cornwall, mostly in the Parishes of Mabe and Constantine. A rough estimate suggests that there is about 1.5 km² of derelict ground in this area which has been affected by quarrying. It is a landscape of deep, steep-sided quarries, usually water filled, and tips composed of large blocks of granite, rejected because of weathering or the presence of flaws. There are also the mason’s yards and, in a few cases, the remains of the cranes used to lift the granite blocks. The wide range of habitats created suggests that there should be considerable biodiversity in and around the old quarry sites.

At the present time most of the activity is mainly concerned with aggregate production at Chywoon and Carnsew quarries, although loads of rubble stone for walling can be obtained from both quarries. Kessel Downs was an aggregate quarry but is currently (2006) inactive. Small amounts of granite for monumental purposes are produced by Trenoweth and Trannack quarries, which both have mason’s yards. There is also some monumental mason’s activity adjacent to Higher Trolvis quarry. In recent years the dimension stone industry has been decimated by competition from granite imported from China, India and other countries where cheap labour is available.

The Carnmenellis granite is entirely a biotite-muscovite-granite. Most of this granite pluton (Fig. 5 – in main paper) is composed of the ‘coarse-grained megacrystic granite – smaller megacryst variant’ of Dangerfield & Hawkes (1981). As was pointed out earlier, this variant seems to contain most of the more important granite quarries in the Cornubian batholith. It consists of potash feldspar phenocrysts set in a matrix of orthoclase and plagioclase feldspar, quartz, biotite and white mica with some tourmaline. The megacrysts are not as large (typically 1-2cm) as in some of the other granite areas and are often aligned in one direction; Hill & MacAlister (1906) suggest this is often in the NNW direction, which assists in the cleaving of the granite in that direction. Leveridge et al. (1990) recognized several sub-types within this granite variant. Towards the eastern margin the granite takes on quite a strong foliation, which may be due to stresses associated with the NNW-SSE strike slip faulting developed close to the granite margin during the time when the granite was crystallizing. There is a marked lack of metalliferous mineralization and quartz-tourmaline veining in the main quarrying areas; Mabe and Constantine parishes may well be the largest area of granite in the Cornubian batholith which has seen little or no post-magmatic alteration, which helps to explain the concentration of quarrying activity in that area.

Hill & MacAlister (1906) reported that texturally “there are two varieties [in the main quarrying area], known commercially as ‘fine grit’ and ‘coarse grit’. The former, which usually occupies the outer belt for an average width of about a mile, although the superior stone, is not so extensively worked as the ‘coarse grit’ on account its being more expensive to dress. It is not only finer in texture, but is darker in colour, containing more biotite, and has a higher specific gravity (about 1%). A good example of this stone is seen at the quarries at Carnsew. The ‘coarse grit is a more attractive stone, and is studded with porphyritic feldspars which reach an inch or more in size, some of the more beautiful varieties of which occur in the parish of Mabe.” Leveridge et al.’s mapping of the Falmouth sheet (1990) indicates that their G_c variety probably roughly corresponds with the ‘fine grit’ and the G_a variety with the ‘coarse grit’.

The core area of the intrusion is occupied by a medium-grained biotite muscovite granite with few megacrysts, which has seen little quarrying activity; although there are a number of elvan quarries (Fig. 10 – in main paper). Hill & MacAlister (1906) attribute this lack of quarrying to intense fissuring in an ENE direction in this granite. The lack of quarries may also reflect the greater distance to the shipping and processing facilities at Penryn and Porth Navas, compared to the quarries in Mabe and Constantine Parishes.

Stanier (1999) provides a detailed account of the history of the granite quarrying industry in this area and the reader is referred to that account for details of the changing quarry ownership. Many structures all over Britain and the world used stone from this area, what follows are a summary.

Borlase (1758) refers to rough hewn granite slabs being sent up to Bristol ‘where are they are further polished for casting thin plates of copper’. It seems that all of the granite extracted in the 18^th century was in the form of moorstone and Smeaton used moorstone for the lighthouse he built in the 1750s on the Eddystone rock, off Plymouth. By 1808 granite cut from moorstone was the principal export from Penryn and by 1818 an estimated 40,000 tones of granite had been shipped for Waterloo Bridge and Chatham Dockyard. Quarrying proper started soon after in the 1820s, at first in excavations no more than 5m deep, but gradually deepening as time went on. By 1840 at least 40 quarries were marked on the tithe map for Mabe parish. In 1840 the Freemans came to the area and gradually became the dominant granite producer. They established a workyard at Penryn, from which port the granite was exported in ever increasing quantities. Granite was also exported from Porth Navas. The major quarries are marked on Figure 10 (in main paper). They include Bosahan (SW729/302), Carnsew (SW760/345), Chywoon (SW747/347), Goodagrane (SW742/323), Higher Spargo (SW749/327), Higher Trolvis (SW743/345), Kessel Downs (SW739/339), Lower Spargo (SW750/332), Lower Trolvis (SW743/349), Maen (SW734/313 & 736/317), Pelastine (SW745/321), Polkanuggo (SW741/347, Rosemanowes (SW736/346), Trannack (SW666/300), Trenoweth (SW759/339), Tresahor (SW742/313) and Trevone (SW748/324). A group of small quarries exploited the granite in the north-western sector near Carwynnen which supplied stone to the Camborne area. Holman’s, the mining equipment manufacturer, developed an experimental underground mine here for testing rock drills, etc. (SW 658/368), which is now operated by Camborne School of Mines for teaching and research purposes.

The outlying mass of granite at Carn Brea supplied moorstone for building in the mining area of Camborne and much granite for railway viaducts and bridges came from a quarry operated by the Great Western Railway. This granite has similar characteristics to the main Carnmenellis mass. Mining showed that this granite is connected at depth to the main Carnmenellis mass.

The Carn Marth mass is also an outlying granite boss north of the Carnmenellis mass, but there is some evidence to suggest that it represents a separate intrusive event. The quality was not regarded as the equal of the granite from Mabe and Constantine Parishes, but several quarries were opened to supply stone for building in Redruth.

Two very small granite masses occur along the north Cornish coast at St Agnes and Cligga, which are more likely to be connected with Carnmenellis than any other granite mass. Cameron quarry at St Agnes exploited a mass of dark coloured greisen, but this quarry was probably more directed towards tin recovery than for producing stone. The Cligga granite is wonderfully exposed in the cliffs around Cligga Head, where a superb greisen bordered sheeted vein system is seen and there has been mining for wolfram and tin. However, as a source of building stone this granite is too altered to be of much use and very little is seen in the older buildings in the vicinity, the pillars supporting the font at St Piran’s Church at Perranzabuloe is one example of greisen, presumably from Cligga, being used.

St Austell, including Castle-an-Dinas and Belowda Beacon

The St Austell granite is the most complex of the granite plutons forming the Cornubian batholith. The eastern part around Helman Tor and Luxulyan is a very coarse-grained biotite granite that was intruded around 285 million years ago. The granite is coarsely megacrystic with large orthoclase crystals up to 15 cm in length, which makes it an attractive dimension stone. Deep weathering has created an extraordinary landscape around Luxulyan of massive granite corestones set in weathered material (regolith) overlying fresh granite at a depth 5-10m.

Borlase (1758) does not mention this granite, but it is frequently seen in medieval churches in the area, such as St Ciricius and Julitta at Luxulyan, St Brivita at Lanlivery and further afield at St Sampson near Golant; all these churches would have used moorstone, blocks of granite up to eight feet long can be seen in Lanlivery Church.

In the 1830s the great Victorian entrepreneur Joseph Treffry developed extensive quarrying operations in the Luxulyan valley (Keast 1982). Initially the granite was quarried to supply stone for major building works such as the surface buildings at Fowey Consols copper mine and for the railway viaduct/aqueduct across the Luxulyan valley, tradition says that these early works were entirely constructed using moorstone. Subsequently Treffry developed Carbean (SX063/577) and Colcerrow (SX065/579 quarries and established a large facility for producing dressed stone at Par, where he built a harbour to export china clay, ore and granite. This was connected to the quarries by a waterwheel powered 800 m long ‘Carmears Incline’ which conveyed the granite down to the level of Pont’s Mill, from where barges conveyed the stone in a canal to the works at Par, later converted to a railway. Ussher et al. (1909) report that “The granite of St Austell has been used in public buildings in Oxford, London and Rome. London Bridge [the one now in Arizona], the British Museum, and Crystal Palace were constructed partly of granite raised from the quarries of the eastern part of the St Austell Granite mass. The stone is used extensively locally, and has also been employed in the Plymouth Breakwater and Lighthouse; the Docks at Keyham, Devonport, Portsmouth, Chatham, Pembroke, Cardiff, Dover, Alderney, and even as far away as Northumberland. Exeter Market Place was constructed from stone raised at Colcerrow, which has yielded the largest proportion of the stone of the district used in the above-mentioned structures.” Keast (1982) also mentions that Luxulyan granite was considered for use in Trafalgar Square. Stanier (1999) reports that Colcerrow granite was also used in Cardiff, Hull, Liverpool, Southampton and Tyne (Northumberland Dock) Docks.

Treffry also built a cutting and polishing facility adjacent to Fowey Consols copper mine, powered by a water wheel, known as ‘The Porphyry Works’. He not only sourced stone from the Luxulyan valley, but also from many other localities around the St Austell granite. He embellished his residence called ‘Place’ at Fowey with the different kinds of stone which he was capable of sourcing from the area, such as Pentewan Stone, Tremore Porphyry, Luxullianite, Topazfels from St Mewan Beacon and Schorl rock from an unknown source. The stones from Pentewan and Tremore are elvans and will be dealt with in the next section. Porphyry Hall at Place is a real tour de force of the granite mason’s art, showing a great variety of granitic rocks as polished slabs lining the walls and forming the tiles on the floor. Unfortunately Place is not open to the general public.

Many different varieties of the Luxulyan granite are to be seen in Porphyry Hall, including one which is stained red by impregnation by iron oxide and another crowded with feldspar phenocrysts. These should perhaps be regarded more as ornamental stones, rather than just building stones. Luxullianite is the most famous stone in that category and has featured in a well known textbook (Hatch et al. 1949, pp. 210-211). It was first described by Pisani in 1864 and is a very striking rock, consisting of pink orthoclase feldspars set in a matrix of tourmaline and quartz. The orthoclase has a microperthitic structure and the tourmaline can be seen under the microscope to occur in two forms: as irregular dark brown grains and as blue needles forming stellate clusters. A detailed discussion of the mineralogy of this unusual rock will be found in Wells (1946). Collins (1878) says that none was known in situ at the time he wrote The Hensbarrow Granite District in 1878, and luxullianite was only known in the form of boulders arising from a supposed east-west vein of luxullianite running through Trevanney Farm about 1.5 km SSE of Luxulyan (SX055/566). Queen Victoria greatly admired this stone on a visit in 1846 and polished stone was sent up to Osborne House by naval ship for incorporation into the fabric. One of the finest boulders was chosen to be carved (at the Porphyry Works) to form the sarcophagus for the Duke of Wellington in the crypt of St Paul’s Cathedral, London. More recently, in Tregarden quarry, 1 km north of Luxulyan village, a vein of luxullianite has been found in situ in this major aggregate quarry, where it can be seen to form a tourmalinized zone about 15-20 cm wide on either side of a thin tourmaline vein. Some poor quality luxullianite occurs on the upper benches in the SW part of the quarry, but the best was found in the lowest bench in the northeast part of the quarry. The quarry has been designated a Site of Special Scientific Interest but, as the quarry is no longer active and flooded, this occurrence now lies beneath 6m of water. This occurrence differed from the original Trevanney Farm occurrence in containing some pyrite. Tregarden (sometimes known as Goldenpoint) quarry was originally a dimension stone quarry, with a reputation of being able to produce very large blocks of granite, but after it was acquired by ECC Quarries it became an aggregate quarry. It closed a few years ago, with aggregate production now coming from an operation exploiting greisened and tourmalinized granite in the upper benches of the western side of Wheal Remfry china clay pit where, occasionally, by some extraordinary coincidence, some veins of granite resembling luxullianite can also be found.

Besides Carbean, Colcerrow and Tregarden quarries, there were a number of other quarries in the Luxulyan valley, including Denders (SX055/585), Carne (SX057/584), Orchard (SX061/567) and Rock Mill (SX059/568). Around 4 km northeast of the Luxulyan valley is Boslymon quarry (SX 081/617) which provided the stone for the rebuilding of Lanhydrock House (NT), two miles to the north, after the disastrous fire of 1881. Large-scale dimension stone working had ceased in the Luxulyan valley area by the end of the 19^th century, but small scale working of granite for monumental purposes continued well into the 20^th century and up to the Second World War (for further details see Stanier, 1999). One of the characteristics of this granite was its ability to be split into long pieces which were ideal for gateposts, lintels, etc. A good example of these granite ‘pillars’ are the supports for the old china clay linhay in front of Wheal Martyn Museum.

Surprisingly little Luxulyan granite is found in the older buildings of St Austell, instead most of the granite in the town seems to have originated from the Carn Grey Quarries (SX033/551 and SX035/552). Carn Grey is a prominent tor immediately above the western face of the western quarry; this partly flooded quarry has been made into an amenity area by the local Council. It is also a Site of Special Scientific interest (Floyd et al. 1993, pp. 187-188). The eastern quarry is steep sided and wholly flooded and inaccessible. These quarries provide one of the few exposures of fresh granite in the south-eastern corner of the western part of the St Austell pluton and as such represent an intermediate type between the western and eastern parts. When fresh the granite is grey in colour and has a pleasing even grain and carves well. It has the texture of the medium- to coarse-grained megacrystic western granite (with feldspar megacrysts up to 4 cm), but the chemical and mineralogical composition is more like the eastern granite. One special characteristic is the presence of megacrysts of biotite up to 1 cm in diameter. The use of this granite goes back a very long way, as it is a curious fact that most of the megaliths in this area (Penrice longstone, Karslake longstone and the Tristram stone) look as if they originated from the Carn Grey area. This may have some ritualistic significance, but is more likely to be because the weathering and jointing of the Carn Grey granite combined to naturally cause megalith-shaped boulders to lie on the ground surrounding the tor, ready-shaped for the Neolithic or Bronze Age peoples to use. One outstanding building built of Carn Grey granite is the listed Grade 2* Market House in St Austell, built in 1844.

A particularly significant type of granite which was mentioned by all the early writers is ‘St Stephen’s Stone’, which was extensively used in medieval and later churches throughout much of mid-Cornwall. This is a pale coloured, almost white, non-porphyritic lithium-mica granite. Slight kaolinization makes the stone easy to work but, providing the stone is chosen with care, it is sufficiently robust to resist weathering well, as the 16^th century Church tower at Probus demonstrates. Most pre-19^th century buildings built of ‘St Stephen’s Stone’ were probably constructed using moorstone gathered from the moors between Nanpean, St Dennis and St Stephen.

This type of granite is also attractive as a fluxing ingredient in ceramic bodies, especially for tableware, because its’ unusually low iron content enables a white fired product to be obtained. When used for this purpose it is known as ‘china stone’ and it has been extensively quarried for this purpose, but not all granites which have been termed ‘St Stephen’s Stone’ would be commercially acceptable as china stones. Many quarries in the area between Nanpean, St Stephen and Treviscoe have yielded this type of pale coloured granite, mostly as a source of china stone. The main china stone area yields a pale coloured (leucocratic) low iron granite with Li-mica replacing biotite, normally containing (when fresh) some topaz and fluorite. An absence of tourmaline is desirable, as this is an iron-containing mineral. A good mineralogical description of china stone from Tregargus quarry will be found in Floyd et al. (1993).

The most famous source of building stone was Cathedral quarry, near Nanpean (SW 956/556), disused since the completion of the Cathedral contract in 1910. Cathedral quarry is so named because it was used as the source of stone for the interior of Truro Cathedral. It is a very leucocratic granite, which helped to lighten the interior of the Cathedral (Listed Grade 1).

Most of the china stone quarries have now been abandoned, such as Tregargus Quarry (SW 949/540), near St Stephen, now a Site of Special Scientific Interest. Some have been backfilled or filled with china clay waste residue, but a small production of china stone is still maintained by Goonvean Ltd at Great Wheal Prosper china stone quarry near Nanpean (SW 955/564) and some random rubble building stone is also produced. An example of the china stone type of granite from Wheal Prosper is to be found in the Boulder Park at Wheal Martyn Museum.

Li-mica granites also occur between Stenalees and Hensbarrow and there were several quarries, which worked this occurrence, both for china stone and as a building stone. The upper, northernmost stopes of Gunheath china clay pit show weakly kaolinized granite typical of this area (around SX 006/571). A specimen of this type of granite is to be seen in the Boulder Park at Wheal Martyn Museum. These Stenalees/Hensbarrow quarries yielded a non-porphyritic granite with an unusually high lithium content (over 3000ppm), sometimes giving the granite a feint purplish hue; occasional inclusions of vividly coloured turquoise can give this granite an exotic touch – see below the east window of St Paul’s Church (Listed Grade 2, built 1849-1851), Charlestown. This stone is superbly displayed in the interior of St Paul’s. The Stenalees/Hensbarrow quarries are now largely filled in or flooded, but are known to have been active in the 19^thC.

Burthy Quarry (SW 919/554, sometimes known as Dyer’s or Chytane), 2km south of Fraddon, is now filled in and buried underneath a china clay waste tip. Burthy granite is one of the earliest quarries in the St Austell area, known to have been active as early as 1811 when it was marked on the 1^st Edition of the Ordnance Survey map (Stanier 1999) and is sometimes referred to by architectural historians. In 1839 De la Beche reported “A much better stone than that usually known as St. Stephen’s granite is obtained at Burthy Quarry, about a mile and a quarter south of Caliquoiter Rock.” It appears to have supplied stone for local building purposes in the St Stephen’s area (see Stanier 1999, p37). Burthy Quarry was probably not a true Li-mica granite, although Ussher et. al. (1909) refer to it containing apatite, topaz and fluorspar; a polished specimen of this granite is known to have existed in the collection of the Museum of Practical Geology in London and is now in the Natural History Museum collection in London. The contact with the metamorphic aureole rocks ran through the western part of the quarry, Ussher et al (1909) report “At Dyer’s quarry, half-a-mile west-north-west of Meledor, the contact is well see between the schorlaceous granite and killas altered to tourmaline-biotite-hornfels and biotite-hornfels”. These aureole rocks were worked as a source of hardcore up to about 40 years ago by Western Excavating Co (a subsidiary of English China Clays), shortly afterwards the quarry was buried beneath a china clay waste tip.

There are a number of other small quarries in the western lobe of the granite in the Fal valley between Virginia and Wheal Remfry china clay pits; Mellangoose quarry (SW 928/564) would be a good example. Probably these quarries yielded rubble stone which was used to construct the many china clay dries (pan kilns) and tanks associated with the china clay industry in the valley. There are doubtless many other small quarries throughout the china clay area which performed a similar function. Some of these worked ‘schorl rock’. However, many ‘old quarries’ marked on the large scale Ordnance Survey maps may have originated as trials for tin or china clay and were not used for constructional purposes.

Very little quarrying of note has taken place in the small outlying cusps of granite exposed around the highest points of the two hills of Belowda Beacon and Castle-an-Dinas, north of the main St Austell granite mass. Belowda Beacon is extensively kaolinized and the area of outcrop at Castle-an-Dinas is very small.

Bodmin Moor

The Bodmin Moor granite pluton is comparable in size and shape to the Carnmenellis pluton. It was intruded 288 million years ago, which is just into the first few million years of the Permian Period. It is a relatively straightforward type of biotite granite, composed mainly of the “coarse-grained megacryst granite – smaller megacryst variant” (Dangerfield & Hawkes 1981) of a similar type to the main granite type making up the Carnmenellis pluton (Figure 10 – in main paper). Notable features of the Bodmin Moor granite are large areas of foliated granite in the northern and western marginal areas and a lack of tourmaline in comparison with the St Austell pluton. Just like Carnmenellis, it also has some areas of fine grained granite in the central area. However, unlike Carnmenellis there are two major faults which appear to down-fault the northern and south-eastern sectors of the granite, the northern fault is marked on the BGS geological map Sheet 335/336. and on figure 42 in Selwood et al. (1998). A detailed account of the Bodmin Moor granite, written by Colin Exley, will be found in Selwood et al. (1998).

Sound granite suitable for engineering work is usually only found in the vicinity of tors and forming the more prominent hills. There has been fairly extensive kaolinization in the Bodmin Moor granite, with two china clay operations at Stannon and Parson’s Park, having operated until the 1990s. Intersections of major lineaments can be shown to be particularly favourable areas for kaolinization. Shallow kaolinization due to weathering is also pervasively developed under the low-lying boggy areas. Metalliferous mineralization is poorly developed in the northern part of the granite mass. As with the Carnmenellis mass, there may be a correlation between areas without veining/mineralization and areas which yield sound building stone. However, there is important copper and tin mineralization in the southeast marginal area, with several important dimension stone quarries (Cheesewring, Golddiggings) close by.

There has been extensive quarrying for granite around the south-eastern and north-western margins of the granite. The north-western area, around St Breward, includes the two presently active quarries at De Lank and Hantergantick, although most of the activity nowadays is centred on the former location. De Lank is a strong silver-grey granite, usually foliated, suitable for high-status architectural and engineering applications. This is the only fully functioning granite dimension stone quarry nowadays in Cornwall, with facilities on site allowing a full range of cutting, shaping and polishing facilities. Historically, De Lank has furnished stone for many important structures. However, it must always be borne in mind that surface boulders on the moor, principally on the hills and scattered around the tors, have furnished large quantities of moorstone, much of which was cut and shaped on the moor to minimize the difficulty of transport and that this has been the main source of granite for pre-19^th century masons.

Floyd et al. (1993) pages 167-169 provide a good description of the quarry’s geology and mineralogy. They describe two types of granite from the De Lank quarry:

“These quarries contain fresh, coarse-grained, poorly megacrystic biotite granite, characteristic of the Bodmin Moor intrusion, strongly foliated and jointed, and containing pegmatite patches, minor granite veins and xenoliths. They also incorporate typical Cornubian, fine grained, megacrystic biotite granite and granite porphyry dykes (‘elvans’)”. The writer would add that De Lank granite, although described above as coarse grained by Floyd et al, is not as coarse grained as many other granites, such as those from the Luxulyan valley. Indeed, Reid et al. (1910) describe it as ‘appreciably finer than most of the other masses of the Cornish granite’ and attribute its notable strength to the presence of interlocking crystals. Also, describing the granite as ‘strongly jointed’ seems anomalous, as one of the features of the quarry is the lack of closely spaced joints, especially at depth in Quarry No 1, where current extractive activity is concentrated. Smith (1999) described the joints as ‘widely spaced’. The foliation is one of the distinguishing characteristics of De Lank granite, which differentiates it from many other Cornubian granites. The foliation has a deformation, not an igneous, origin, and is related to late strain during cooling on an adjacent major strike-slip fault. Reid et al. (1910) also comment that one of the outstanding attractions of this granite is its freedom from stained or discoloured areas and say that it is almost unrivalled in this respect. De Lank is a Site of Special Scientific Interest. Several east-west felsitic elvan dykes cross the site. A deep cutting along the line of one of the elvans provides access to the site.

In the De Lank group of quarries No. 1 Gully quarry (SX 100/755) is the currently active quarry; Hantergantick quarry is about 400m NE of Gully quarry, on the north bank of the De Lank river but, as far as the writer is aware, is not currently active. The De Lank quarries were once connected to the Wenford Bridge railway branch by a short spur and incline down the steep valley side to the branch line, by which it could be taken to Wadebridge for shipment, nowadays all stone is removed by road. Granite quarrying for dimension stone started in mid-19thC and has continued up to the present (see Stanier 1999, pp. 32-33 and 151-152 for full history). A good account of De Lank quarry in 1907 is also in Stanier (1999). Current quarrying practise is described in Smith (1999), pages 243-244. Hantergantick opened in 1918 and closed in 1997.

De Lank granite has been extensively used in lighthouses: Eddystone, Smalls, Beachy Head and Bishop’s Rock lighthouses are built of it. Tower and Blackfriars Bridges also use it and the Royal Opera House, Trafalgar Square. More recently, the Princess Diana fountain and the courtyard at Burlington House, Piccadilly have been built from De Lank granite, as well as the New Parliamentary Building, Westminster and the Commercial Union Head Office in London and Royal Exchange Square in Glasgow. The latest structure to be created from De Lank granite is ‘The Seed’ for the Eden Project, which is claimed to be the largest single piece of granite ever crafted in southwest England. Further afield, many other buildings and engineering constructions such as docks in Hull and Mumbai (Bombay) have used the stone in the past.

Recent uses for Hantergantick granite include St Ives Lifeboat station, Campbell Park, Milton Keynes and as building internals in the DTI Building, London. See Appendices of Stanier (1999) for full list of buildings and engineering structures which used De Lank granite.

The Tor Down group of quarries is situated just to the west of St Breward (SX 094/767 & 094/766) and is said to have been the first of the quarrying areas on the west side of the Bodmin Moor granite be opened up, it continued in operation until the early nineties; it is listed as active in the National Stone Directory (1998-1999). Stone for the Britannia Royal Naval College came from here. The northern of the two quarries is flooded and most recent activity has been in the southern quarry.

Further into the moor were a group of small quarries near Carbilly Tor (SX 127/755). Selwood et al (1998) report that the central quarry of the group (SX 1258/7549) contained aplite or aplogranite veins in the biotite granite with feldspar megacrysts up to 4mm; the feldspar was a microcline microperthite. The quarries were: Carbilly quarry on the west side, Bedwithiel quarry on the east side and Bradford quarry in the centre. After many changes in ownership these quarries had all ceased operation by the 1960s and are all are now flooded. There were also small quarries in the southwest corner of the granite, near Cardinham.

On the opposite side of the granite a major group of quarries existed, grouped around the Cheesewring. De la Beche does not mention any quarry in this area in his 1839 report and it appears that quarrying did not seriously commence until the Liskeard and Caradon railway had reached the south side of Stowe’s Hill adjacent to the Cheesewring quarry in 1844. By means of the railway and the Looe canal, the dressed granite could then be taken to Looe, 15 miles away, for shipment. The canal was converted in 1860 to a railway, allowing direct shipment from quarry to port.

The granite of the Cheesewring is a durable silver-grey granite, weakly porphyritic with feldspars about an inch long, intermediate between the finer and coarser varieties of Cornish granite (Reid et al. 1911). It has a feint foliation with a northerly dip. Occasional xenoliths containing andalusite and sillimanite are seen. The way in which the sub-horizontal joints parallel the surface and increase in frequency towards the surface is well seen in this quarry. The vertical joints are mineralized with quartz, tourmaline and small amounts of metalliferous minerals.

The Cheesewring quarry provided stone for many famous structures. The stone for the Spithead, Thames and Medway forts was supplied from the Cheesewring in 1868 and in the 1870s stone was used for the Albert Memorial and the Guards Memorial in the Crimea. In the 1920s Cheesewring stone was used for the King George V dock in Calcutta and for Lambeth Bridge. Reid et al. (1911) report that the stone was used in the Bull’s Point Powder Magazine and the Pier on the Tamar at Plymouth, for the Guard’s Memorial in Waterloo Place and for the pilasters of Westminster Bridge. Stanier (1999) also lists Birkenhead, ‘London’, Southampton and Copenhagen Docks; Devonport Dockyard, Portland and Alderney Breakwaters, Great Basses (Ceylon) and Fastnet lighthouses, Tower and Rochester Bridges, the Embankment and the Great Exhibition Memorial, London.

The Cheesewring quarry has not been actively worked for many years, but there has been some activity concerned with removing large boulders from the finger tips for use as armourstone.

Gold Diggings quarry (SX 249/7240 is situated about half a mile west of the Cheesewring quarry and worked a silver-grey granite of similar appearance. There were many other small quarries started in this area; railway spurs to quarries on the south-west side of Kilmar Tor (SX 249/747) and on the south side of Bearah Tor (SX 260/745) were constructed in the 19^th century. There is still some activity at the latter site, where granite blocks are being dressed for monumental work.

There are two areas of granite between Bodmin Moor and Dartmoor, at Kit Hill and Hingston Down. These granites appear to be cusps arising from a buried ridge of granite connecting the two moors. The Kit Hill granite has seen extensive quarrying activity for dimension stone, but the Hingston Down granite is less suitable for dimension stone production, although a large aggregate quarry is presently active in this small granite mass.

The Kit Hill granite is another silver grey granite similar in character to the granite quarrying areas of the Carnmenellis and Bodmin Moor plutons. It is a standard non-porphyritic biotite granite, typical of the Cornubian batholith, with nothing exceptional about it. It is medium to coarse grained (Reid et al. 1911). The best stone came from the northern quarries, possibly because they were deeper, giving access to fresher granite. The quarries had the reputation of yielding large blocks of stone (Reid et al. 1911). Good accounts of the archaeology and the history of quarrying are contained in Herring & Thomas (1990) and Stanier (1999, pp.24-27).

The area quarried forms a complex of three large early 19^th C quarries on the southern slopes of Kit Hill (SX 376/712) and a complex of two large quarries on the northern side of the hill (SX 374/717); the latter operated until 1955. There is also abundant evidence all over the hill of early moorstone working (see Herring & Thomas 1990).

A large number of significant structures have used this granite. Herring & Thomas (1990) report:

“Kit Hill granite was used on a number of important public works: Millwall and Tilbury docks, Lambeth and Putney bridges in London, and Singapore dock; London Bridge (1935; Blackfriars, Battersea, Chelsea, and Waterloo bridges; Bishop’s Rock and Hanois (Guernsey) lighthouses, Devonport dockyards, Plymouth streets, Thames embankment, Beatty and Jellicoe memorial in Trafalgar Square, Gibraltar dockyards (W.M.N. 28.10.1955) and the last major project, Battersea Park Wall”.

In addition MacAlister in Reid et al. 1910 reports:

“The quarry on Kit Hill which is in the hands of the Kit Hill Granite Company has been worked continuously for upwards of 25 years, and occasionally as many as 200 men have been employed in raising and dressing the stone. Blocks of great size can be supplied from these quarries. The manager, Mr. F.R.L. Chalk, informs us that the stone has been employed by the Admiralty, Metropolitan Board of Works, Trinity House, and many other corporations, etc. The whole of the stone , some 70,000 cubic feet, for the bridge over the Thames at Battersea was supplied from these quarries. When contracts for stone are not being carried out, the men are employed in making brick-shaped setts for roads and buildings”.

THE ELVANS

For ease of description the elvans have been grouped into a series of areas:

Penwith

Comparatively few elvan quarries have been identified in this area. However, Reid and Flett (1907) report that throughout the killas area the elvans have been extensively used for building and that elvan was preferred to killas for building engine houses.

A curious rock, first mentioned by De la Beche (1839) at Escall’s Green (Mayon) appears to form a band 50m wide striking NW-SE across the Penwith granite from Porthcurno to near Sennen (Reid & Flett 1907). Whether this is a true elvan must be doubted; it may be better described as a massive dyke of aplite or microgranite. A hand specimen from a small flooded quarry beside the school at Escall’s Green (SW 363/261) shows a pale creamish pink fine grained quartz/feldspar rock with scattered patches of quartz-tourmaline (schorl rock) about 1 cm across and scattered small bipyramidal crystals of quartz, cut by thin veins of tourmaline and quartz. De la Beche says it has a handsome appearance when polished, so presumably at one time it must have been exploited as a decorative stone. No buildings where this stone has been used are known.

Small quarries in elvan are mentioned by Reid and Flett at Heamoor (SW 465/317), South-west of Gwallon (SW 520/315), Collorian (SW 524/348) and Canon’s Town (exact location not known). The rock is described as ‘quartz-feldspar porphyry with porphyritic crystals of orthoclase’. A small quarry in non-porphyritic fine grained elvan 0.5 km north-east of St Erth Church (SW 554/354) lies beside the famous occurrence of late Pliocene St Erth Beds. Stone from this quarry was probably used in vernacular building in St Erth village.

Carnmenellis granite and Truro area

The Carnmenellis and St Austell areas, are the two most important areas where elvan has been exploited for building stone. The Carnmenellis area includes the urban centres of Truro, Falmouth, Camborne and Redruth where much 19^th/early 20^th century building contains elvan masonry. Unlike the St. Austell, St. Agnes and Cligga masses, there is not pervasive kaolinization of the granite, so that elvans within the granite envelope are not appreciable altered.

There are three elvan quarries in the northern outlying Carn Brea granite mass. Beside the railway, 1.5 km east of Camborne Station (SW 663/403) is the small trench-like overgrown Brea quarry, which worked a narrow (2-3m) wide elvan, oriented NE-SW which is said to have yielded a typical hard elvan, probably used for building in adjacent Camborne. A large quarry on the northern slopes of Carn Brea (SW 679/408) yielded an elvan which Hill & MacAlister (1906) describe as ‘a fine textured elvan’. However a sample collected recently showed a very coarse grained elvan crowded with feldspar phenocrysts up to 2 cm long. This is probably similar to the elvan which was worked in a quarry at the east end of Carn Brea (SW 689/410) which Hill and MacAlister describe as being unusually coarse in texture with a large number of phenocrysts of quartz, orthoclase and chloritized biotite lying in a microgranitic groundmass of quartz, orthoclase and scaly muscovite.

A quarry formerly existed on Illogan Downs which supplied stone for the building of Tehidy House. It was described by Borlase (1758), De la Beche (1839) and others. Borlase says “Of the finer closer grit still is the free-stone raised on Illogan downs, of which the eastern front of Tehidy House is mostly built. The ornaments of the portal and windows and cornice are of Portland, but the main body of the Cornish stone, which is so near the texture and colour of Portland, that it requires a very near inspection to distinguish one from the other. It unfortunately rises in such small masses, that it will seldom square to one foot and a half in block; and in this quarry there is so little found of it, that there was scarce enough to finish the front below the cornice.” Worth (1875) also mentions the use of Illogan elvan at Tehidy House. Hill & MacAlister (1906) say the dyke hades to the north-west at a very low angle. Also “In these dykes the original orthoclase phenocrysts have frequently disappeared. Under the microscope the original quartz phenocrysts are bounded by a secondary outgrowth in optical continuity, while the felspars exhibit a similar structure.” An elvan is marked on the geological map (Sheet 352) in the Illogan area, but the exact location of the quarry is not known, as it was probably built over long ago.

A cluster of significant elvan quarries lies in the centre of the Carnmenellis granite mass, which must have supplied large quantities of building stone for use in adjoining villages and towns. One of the few quarries which is still open is Polmarth quarry, west of Stithians reservoir, at the foot of the southern slopes of Carnmenellis Hill (SW 699/357). It is 12-15 m wide, with a horse of granite in the central part of the quarry. Hill & MacAlister (1906) say that it hades steeply to the north-west. It is the fine grained type of elvan, with small phenocrysts of quartz, feldspar, biotite and feldspar, flow banded at the margin. The quarry is about 100m long and 15-20 m deep. Although many other significant elvan quarries are known to have existed in the central part of the Carnmenellis granite and are marked on older maps; they have all now been filled with landfill – Treservern Croft (SW 716/372), which was probably in the same elvan as Polmarth), Praze (SW 639/354), Carvath (exact location not known) and Carthew (SW 685/360). Elvan from a quarry at Hangman’s Barrow (SW 675/366) has been reported to have been used for building in Redruth. Brief descriptions of most of these quarries will be found in Hill and MacAlister (op. cit.). Few, if any, elvans have been exploited in the main area of former dimension stone working in Mabe Parish (CP); an area which also lacks significant metalliferous mineralization.

The BGS geological map (sheet 352) shows many elvans intruded into Devonian slaty rocks between the eastern margin of the granite and Truro, many will be known only from underground metalliferous mine working. Significant quarries (over 100m long) at Creegbrawse (SW 746/437), Pencoose (SW 775/403), and Kerley (SW 760/439) have been landfilled, but the quarry at Saveock (SW 763/449) may still be open. It was first described by De la Beche (1839) who noted: “that at Saveock Water, near Chasewater, with a grey granitic base, containing a somewhat roseate feldspar and radiated masses of schorl, looks well.” Hill & MacAlister (1906) provide a detailed description . “This well-known elvan has long been quarried at Saveock Water. It is characterised by schloraceous nests and patches which sometimes attain an inch in size. The dyke hades north-west, and the quarry is traversed by a cross-course. The porphyritic constituents are feldspar, which are about a quarter of an inch in size, and quartz blebs. Under the microscope the phenocrysts of quartz and orthoclase are seen to be idiomorphic, the quartz showing few signs of corrosion and filled with large cavities with mobile bubbles. Many of these cavities are negative crystals, and some contain small transparent cubes. The porphyritic crystals are much decomposed, but are mainly perthitic orthoclase, although some are possibly oligoclase. A curious feature is the presence of porphyritic groups of micro-pegmatite. Some of the porphyritic quartz is surrounded by an ill-defined narrow halo of smaller quartz grains in optical continuity. The matrix is a microgranitic aggregate of quartz, cloudy untwined feldspar, and fine scales of muscovite. Chlorite is also present, often in radiate bundles, fairly dichroic. The tourmaline is practically confined to the rounded patches seen in the hand specimen. It forms small irregular grains, highly pleochroic, in shades of blue, bluish green, and pink, and appears to fill up the intertices between the grains of quartz, which constitute the remainder of the aggregates. It never yields perfect crystals and occasionally forms radiate groups. The structure of these patches is not poikilitic, but in some parts of the section there are small poikilitic areas. Larger crystals of quartz occur in them, evidently phenocrysts, and lead to the conclusion that these rounded sports are due to tourmalinisation.”

Further south is an elvan quarry at Enys (SW 795/365), the former home of John Davies Enys (1837-1912), who was interested in geology. Elvan stone from the quarry on the Estate was used in the 19^th century Enys House and a collection of large specimens forms a rockery in the garden which contains many interesting rock types from Cornwall and elsewhere.

Nearer to Truro is the large elvan quarry at Nancevallen (SW 813/440 – 812/439), which is still open. This quarry is trench-like in form and extends in a NE-SW direction up a steeply sloping hillside; at the upper end the elvan can be seen to change direction and abruptly terminate. It must have supplied stone for much Victorian and Edwardian building in Truro. Hill & MacAlister (1906) report: “This dyke, which hades steeply to the west, is probably at least from 25 to 30 feet thick. It is a granite porphyry, with porphyritic feldspar, quartz and biotite. These felspars attain an inch in length, while occasionally the biotites are equally large. The quartz occurs in bleb-like forms, which sometimes exceed a quarter of an inch. The groundmass of the rock is rather coarse. For several feet from the edge of the dyke the porphyritic crystals are absent, and this portion of the rock is sometimes (flow) banded.” A field visit confirmed this description and specimens were collected. No backfilling of the quarry has taken place.

About 1km south of Truro City centre is the large Newham elvan quarry (SW 830/437) which has been worked back into hillside on the west bank of the Truro River estuary. This is an important quarry which still has a large face visible. The quarry appears to have supplied stone for the early 16^thC St Mary’s aisle of the Cathedral and it was extensively used in 18^thC and early 19^thC buildings in Truro, especially Lemon Street which Pevsner describes ‘Lemon Street is one of the most completely Georgian streets preserved anywhere, all two-storeyed, stone fronted houses of uniform character’. Mentioned by De la Beche (1839); but Collins in 1878 describes Newham as ‘formerly worked’. Not mentioned in the 1895 list of quarries in Cornwall (Anon. 1895). Probably not worked since the railway and gasworks were built across the entrance in the late 19^thC.

The Newham elvan trends ENE-WNW and is a pale cream coloured fine grained rock when freshly cut and appears relatively uniform (compared to some other elvans) across the width of the face which is 25-30m in width and about 18-20m high. Slaty rocks are exposed on the south side but the northern face appears to be still in elvan. Joints dip steeply northwards in the main face, suggesting the elvan may dip at this angle as well. In some buildings (but not in the quarry) this stone can resemble a siltstone, as it has a certain amount of fissility, which suggests a strain was placed on the elvan during or soon after emplacement. Occasional thin quartz veins are also seen. The stone is an attractive cream or creamish-white in colour, not unlike Bath Stone when seen from a distance. It superficially resembles Pentewan Stone, but does not appear to stand up to weathering quite so well. It can be easily carved, although it is sometimes fissile, with occasional quartz veins.

De la Beche (1839) reports: “At Newham quarry, near Truro, at the termination of a long dyke extending about nine miles from the westward of Penstruthal, where it cuts through the granite, even the porphyritic character becomes lost, and we have a substance not unlike some arenaceous rocks. It is white and rather friable – a fine-grained compound of quartz and porphyry. A short distance west, however, the elvan is a well-characterized porphyry. Worth (1875) mentions Newham, and says the stone is much used in Truro. Collins (1881) describes it as being remarkably fine grained, showing almost no porphyritic character and provides an analysis of the elvan from Newham quarry, which is reported in the memoir. The loss on ignition figure of just over 2% would seem to indicate slight kaolinization and this may explain why this elvan does not stand up to weathering quite as well as the Pentewan elvan.

Water (hygroscopic) 0.24

Water combined (L.O.I.) 2.04

Silica 72.88

Alumina 14.47

Ferric oxide 2.45

Manganous oxide 0.82

Lime 0.10

Magnesia trace

Potash and Soda 7.15

Lithia and Fluorine trace

Hill & MacAlister have surprisingly little to say about Newham, suggesting the quarry was not being actively worked at the time of their survey (map published 1906).

South of the Carnmenllis granite, in the area around Mawgan, there is a group of NE-SW oriented elvans which have been worked in some small quarries. In the fields south of Rosevear (SW 699/242), 1 mile SW of Mawgan, two small quarries were opened in two parallel SE dipping bands of elvan, now almost lost in overgrowth. Flett & Hill (1912) say “The elvans have also been used for building and constitute an excellent stone, especially the band near Rosevear….”. The stone used for the entrance lodge to the Trelowarren Estate 0.5 km south of Mawgan village appears to resemble this elvan. However, this elvan does not appear to have been used for Trelowarren House and its outbuildings.

NW of Mawgan village is a large quarry (SW 705/255) beside the road up through the woods. Flett & Hill (1912) say: “It is a coarse-grained biotite elvan, hading to the south-east, with abundant phenocrysts of quartz and small turbid felspars. Bleached and weathered biotite is more abundant than usual in rocks of this class. The matrix is micropoikolitic to microgranitic, with graphic haloes around the quartzes. This rock, as seen in the quarry north-west of Mawgan, has a parallel structure and looks slightly sheared, with the biotites oriented, but under the microscope this structure is not very apparent.” A visit to this quarry showed a rather decomposed elvan and the sheared material described by Flett & Hill; it would not make a good building stone, so the quarry probably mainly supplied road making material.

St. Austell area

The St Austell granite has many elvans, mostly orientated east-west, associated with it and the majority of china clay pits show at least one elvan, usually as a steeply inclined dyke, but occasionally, as in Dubbers china clay pit, of sill-like form. The elvans in the St Austell granite area are almost invariably kaolinized to a greater or lesser extent. The less kaolinized varieties can look relatively robust when first excavated, but after exposure to normal weather for a few years, they usually disintegrate. The loss on ignition figure (L.O.I.) given in a conventional whole rock analysis is a good guide to the presence or absence of kaolinization in an elvan. If it is more than a few percent, then it is suffering from kaolinization to some degree and will not stand up to normal weathering when incorporated into a building. As an example: the hardest possible elvan from a china clay pit was sought for the Boulder Park at Wheal Martyn Museum (Bristow 2006). A robust looking boulder from Wheal Remfry showed a L.O.I. of 5.13%; unkaolinised granite is typically just over 1% L.O.I. and completely kaolinized elvan will be in the range 5-10%, depending on the mineralogy and the degree of greisening, etc. So the Wheal Remfry elvan is, in fact, quite strongly kaolinized and it has now (2012) disintegrated. This elvan was used for brick and tile manufacture, in the Wheal Remfry Brick and Tile Works, which closed in 1972 (Ferguson & Thurlow 2005). It is a fact that only the elvans which are at least 2 km from the granite margin have been quarried for building stone, due to this pervasive kaolinization. For this reason there are no entries for elvan quarries in the granite. Similarly, elvans in the Goss Moor area are all kaolinized to a greater or less extent and also will not be mentioned here.

Pentewan Stone is the most famous of the elvans in the area surrounding the St Austell granite and has been used in many historic and listed buildings. It has not been worked since the late 19^th century, although some beach boulders have been removed in recent years for repairs to Holy Trinity Church in St. Austell (Coode, undated). A recent sculpture by Karl Williams is shown in Figure 12 (in main paper). There are three quarries:

Quarry 1 (SX 025/475) adjoins the coastal path, and is an WNW-ESE cutting at the top of the cliffs above Polrudden Cove, probably not more than 7-8m deep. The top of the elvan can just be seen in the east face of the cutting, about halfway along. A rockery at Polrudden farm has been constructed from stone reclaimed from the tips associated with this excavation.

Quarry 2 (SX 026/476) forms a ravine like feature in the cliff and may have been the principal source of stone for medieval masons.

Quarry 3 (SX 022/478) is a NW-SE ravine-like feature 700m north of Pentewan Square on the eastern side of a steep sided valley, probably not more than 10m deep. An adit just north of the quarry may have been opened to drain the quarry, but its offset position to the north of the quarry (i.e. down-dip) suggests that it might be part of an attempt at underground working to obtain fresh unweathered stone, perhaps by Treffry’s masons when they were working on Place House, Fowey in the 1830s.

Pentewan Stone comes from a fine grained elvan dyke dipping in a northerly or north-easterly direction at about 30-40^o (Fig. 11 – in main paper). The NW-SE strike of the elvan is anomalous and, as was mentioned earlier, it appears to follow the strike of the Start-Perranporth fault line. The country rocks alongside the elvan are intensely sheared slaty mudstones of the Polglaze Formation (Leveridge 2008), a fault breccia associated with the main fault line of the SPL is also seen in Polrudden Cove. In the cliffs two branches are seen; the more southerly is the more attractive and uniform stone (Quarry 2). The north-eastern branch continues northward along the base of the cliffs for 0.5 km. In places the elvan tends to be spoilt (from a mason’s point of view) by many xenolithic inclusions of slate, granite, etc., particularly at the margins. Both branches are about 2-5m thick but vary in thickness considerably. In the fields between Quarry 1 and Quarry 3 the elvan appears to pinch out altogether. There is conspicuous flow banding at the margin and the elvan tends to become slightly coarser towards the centre. Teall in Reid and Flett (1907) describes it: “A light grey or cream-coloured quartz-porphyry composed of phenocrysts of quartz and more or less altered orthoclase in a micro-crystalline felsitic matrix. A few scattered plates of muscovite occur also as phenocrysts and minute flakes of the same mineral form a not inconsiderable portion of the ground mass”. Mottershead (2000) reported that XRD studies of Pentewan Stone taken from old buildings showed only quartz and mica, which suggests the elvan has been greisened. This is a common feature of felsitic elvans and will increase durability because, after greisening, there is little or no feldspar left in the rock for weathering to attack. Leveridge (2008) also described the elvan, but seems to have found more feldspar than Reid or Mottershead.

Pentewan Stone is a pale grey or creamy coloured stone, not unlike Bath Stone when viewed from a distance. It is a true freestone, as can be seen in the carvings on St Austell Church tower and at Place House, Fowey and in recent sculptures (Fig. 12 – in main paper). When freshly cut the stone has a yellowish tinge, but extended weathering over many centuries transforms the stone into a silvery-grey colour, as can be seen at Antony House and other country mansions. In more polluted surroundings the stone takes on a yellowish-grey colour with time. De la Beche (1839) comments:

“For durable stone, the harder elvans of the district, particularly when of cream or other light colours, may be considered as the best building materials in it; their durability and appearance may be seen in many churches and old mansions, where the finer carvings of the ornamental parts are as sharp as the day they were put up… Pentuan stone is more readily sculptured than might be expected”.

A 5^th/6^thC inscribed slab in St Cuby (Tregony) Church is Pentewan Stone. Both Leland (1534) and Carew (1602) mention Pentewan Stone as one of the finest freestones in Cornwall. It was used extensively in 14^th-16^thC Churches as well as many other high status buildings. Pentewan (sometimes spelt Pentuan) Stone has been used in the following structures: Antony House, Torpoint (Grade I); the Chapel, Trelowarren (Grade 1), St Austell Parish Church (Grade 1); Place House, Fowey (Grade 1); St Mawes Castle (Grade 1), Bodmin Parish Church (Grade 1), Charlestown Chapel (Grade II*), Numbers 1/1a, High Cross Street, St Austell, plus many others, particularly Churches. Used as far afield in the Middle Ages as North Cornwall (St Endellion) and Trelowarren. It is also reported to have been used in the Citadel, Plymouth, but otherwise not used outside Cornwall.

Quarrying continued up to the late 19^thC, Worth (1875) says there was still some working at that time, but by the time the Survey Memoir was written (Reid & Flett 1907) working had ceased. The stone was shipped out directly from Polrudden Cove; the remains of a crude wharf are still visible in the cove. Several ships trying to load stone were said to have been wrecked because of the exposed situation.

There are several other small quarries to the north of Pentewan, including one at Levalsa farm, but little is known about them. A pair of quarries either side of the road at Castle Gotha (SX 027/498), now filled in, were described by the Geological Survey (on the 6” map) as a ‘whitish elvan about 20’ wide in slates’. Nearby Georgian Penrice House is built of a whitish elvan, which is not Pentewan Stone, it could well have come from these quarries. A similar whitish elvan also forms the string course at Menabilly, the ancestral home of the Rashleighs and former residence of Daphne du Maurier.

In Penrice Woods, about half a kilometre north of Penrice House, there is a small quarry beside a farm track (SX 023/505) which yielded a pale yellowish cream elvan with large feldspar phenocrysts up to 2 cm across. This stone was used in 19^th century St Levan’s Church at Porthpean and sundry other buildings in Higher Porthpean village. From a distance this stone looks exactly like Pentewan Stone, but on closer examination the abundant large feldspar phenocrysts show this must be a different elvan.

Several elvans, forming part of the suite of elvans along the SPL, were encountered in the famous Polgooth tin-mine, and it would not be surprising if some elvan building stone originated from the underground workings of the mine. The porphyritic Polgooth elvan extends from just north of London Apprentice to Hewas Water/Pothole and beyond and there are a number of quarries along its length which have yielded building stone. Just north of London Apprentice on the opposite side of the valley to Molingey dolerite quarry was a small quarry in the elvan, just south of Molingey Mill, (SX 007/502). No further details known. A long quarry to the south of Polgooth (SW 997/503) is in this elvan and yields a rather soft somewhat decomposed stone, which has probably been used in vernacular buildings in Polgooth. The Trelowth elvan quarry 0.5 km east of Sticker (SW 985/504, now filled in) was also on the Polgooth elvan and yielded a fine grained elvan with large feldspar phenocrysts up to 1 cm, mostly kaolinized, which weather out leaving pseudomorphic cavities and was used in the Old Cottage Hospital, Edgecumbe Road, St Austell, where it may still be seen. Further west along the elvan, 1 km north-west of Sticker, there were several quarries (SW 971/506 and SW 974/506) on either side of valley just north of Pothole. The western quarry is possibly still open, but the eastern quarry is filled in. The eastern quarry was the larger and must have supplied a significant amount of stone. A short distance further east, in the excavations for the Sticker by-pass a thoroughly kaolinized elvan was seen, emphasising how variable the kaolinization can be. Many buildings in Sticker are built of elvan, which could well have come from these quarries. Some buildings in St Austell use a softer elvan with some iron staining (e.g. the arches at the rear of the Market House) which also may have come from these quarries, or possibly the Polgooth quarry. There are three quarries close to the road between Sticker and Downderry (SW 970/508, SW 965/508 and SW 963/508), all in the same elvan, possibly a continuation of the Polgooth elvan. Ussher says 25 feet of elvan was exposed in one of these quarries, which yielded large blocks for local use presumably. Small quarries near Carnwinnick (=the white rock in Cornish, SW 928/515) and north of Trethullan Castle (SW 972/515) are reported by Ussher et al. (1909) to have been in another elvan. The latter may be in the same porphyritic elvan as was seen in the roadworks at the eastern end of the Sticker by-pass (SW 994/514).

The short Brannel elvan is exposed in two quarries (SW 954/518 and SW 956/518) either side of the hill just NE of Coombe and just south of the farm called Brannel – this elvan is not marked on 1:50,000 Geological Survey Sheet 347, but was said to have been worked for stone for St Mawgan and St Eval airfields during the Second World War, according to reliable local sources. Ussher says this elvan is “…about 30’ wide. This rock is broken, by nearly vertical east and west joints meeting irregular joints, into blocks sometimes over a cubic foot in size.” Ussher (op. cit.) also suggests that this elvan may be connected with that encountered in the workings at nearby South Terras uranium mine. A field visit confirmed the existence of quite a large quarry, unencumbered by waste, with large faces up to 15 m high. Extraction of small amounts of stone for restoration and small projects would be a possibility at this location, providing the appropriate permissions could be obtained. A detailed paper by Hawkes et al. (1975) gives much petrographic and chemical detail. Quartz, sodic-plagioclase and potassium-feldspar megacrysts are set in a fine matrix of quartz, feldspar and mica with an average grain size of 0.02mm. Some feldspar megacrysts show a core of plagioclase, surrounded by a potassium-feldspathized zone, in turn surrounded by a sericitized zone, indicating late stage greisening. There is little evidence of kaolinization and the chemical analysis (below) confirms this with a low L.O.I. The elvan was said to be 10-13 m wide dipping roughly at 70-75^o to the NE, striking NW-SE. Flow banded fine-grained margins are not well developed. Rb/Sr dating gave an age of 270 +/- 5 Ma which corresponds with the age of the western lobe of the St. Austell granite. An analysis was given:

SiO₂ 73.53

Al₂O₃ 14.14

Fe₂O₃ 0.48

FeO 0.8

MgO 0.34

CaO 0.55

Na₂O 1.93

K₂O 5.94

L.O.I. 1.5

One of the most striking and attractive elvans in Cornwall occurs at Tremore, north of the St. Austell granite, and about halfway between Withiel and Lanivet. This stone has been used not only for building, but also for decorative purposes. It is often referred to in the older literature as ‘Tremore Porphyry’ (Fig. 14 – in main paper) and, as will be explained below, is Cornwall’s ‘Royal Porphyry’.

There are two overgrown quarries on either side of the valley a few hundred yards below Tremorebridge, (west bank SX 010/648, east bank SX 010/647). Active quarrying is mentioned at length by De la Beche (1839) and in the Bodmin and St Austell Memoir (1909). The use of Tremore porphyry in King Arthur’s Hall at Tintagel (built late 1920s – early 1930s) and in the Baptistry at St Austell Parish Church (1923) suggests that some extractive capability may have extended up to just before the Second World War. The quarry is now inaccessible due to vegetation and high unstable faces.

The Tremore elvan extends for over a kilometre either side of the quarries at Tremore and is part of an extensive set of east-west elvans which are associated with bands of calc-flinta (see geology section in main paper for an explanation of this term). All of the rock which can presently be seen in the quarry faces at Tremore is calc-flinta, which may have been worked as a source of aggregate and hardcore. The Tremore elvan appears to be a steeply dipping feature, but none of the accounts say how wide it was; one must assume it was 5m+ or thereabouts, it might be much wider.

The Tremore elvan is highly variable in appearance. The chilled margins are distinctive, but the main rock of interest is the coarser grained interior of the elvan which shows white feldspar (orthoclase, up to 3-4 cm in length) and grey quartz (up to 0.5cm in diameter) phenocrysts set in fine grained reddened matrix (Fig. 14 – in main paper). Spherulitic aggregates of black tourmaline up to several mm in diameter are variably present, sometimes being as important a component of the rock as the feldspar or quartz phenocrysts. Microscopic examination of the rock shows that there is much fine fluorspar and fine mica, presumably indicating greisenization. The red colour is due to fine iron oxide particles; Tremore elvan is sometimes pink, sometimes dark red, occasionally without oxide staining and pale grey. All these variations are beautifully displayed as polished panels and tiles in Porphyry Hall which was created by the great quarry master Joseph Treffry in the 1830s at his former residence Place, Fowey. For a detailed discussion of the geology and mineralogy see Barrow & Flett in Ussher et al. 1909, pp. 73-79.

The Treffry records say that the porphyry at Place came from ‘Brynn’, but there is no record of an elvan there; in view of De la Beche’s clear confirmation that the stone came from Tremore, we must assume that the reference to ‘Brynn’ is misleading. However, other writers do seem to suggest that some stone may have been obtained from other points along the line of the elvan outside the Tremore valley.

De la Beche (1839, pp. 501-502) describes this stone at the time it was being worked and was being used to build Porphyry Hall, so his description is most helpful:

“Many of the hard elvans are very beautiful, when worked and polished, particularly those which are most porphyritic, and in which there is much contrast between the base and the contained crystals. The most remarkable are, probably, those which are obtained from the dykes extending from Tremore, near Bodmin, towards the east, on the south of Withiel and St. Wenn. They vary much in colour, but that with a reddish or flesh-coloured base, in which there are white crystals of feldspar, and occasionally some of quartz and schorl (schorl = tourmaline), is the most beautiful, and occurs in large quantities at Tremore village, and in the ravine through which a brook flows to Ruthern Bridge. Mr. Austen Treffry has caused this reddish porphyry to be cut and polished by means of water power, at Fowey Consols Mine, for his house at Fowey, where it is employed, mixed with the schorl rock above noticed, for pavement and steps (the main period of building at Porphyry Hall was shortly after this was written by De la Beche). It has a very handsome appearance, and may be obtained of large size, blocks being found up to five or six tons in weight… …There is one variety which may be obtained in fair quantities at Tremore, in which light pink crystals of feldspar, with others of quartz and schorl, are embedded in a brownish flesh-coloured felspathic base. Another, of which we only found small portions, contains greenish feldspar crystals in a light coloured base.”

Shortly after De la Beche’s visit, Queen Victoria and Prince Albert visited Place in 1846 and on entering the recently constructed Porphyry Hall the Queen exclaimed ‘This is magnificent’; so Treffry presented some polished slabs to the Queen, which were taken by naval ship to Osborne House on the Isle of Wight, which was being built at that time, so Tremore Porphyry really is Cornwall’s ‘Royal Porphyry’! It certainly is very attractive when slabs are polished for use in facing or as tiles.

Tremore Porphyry has been used in Porphyry Hall, Place, Fowey (polished slabs), (Grade 1); Osborne House, Isle of Wight (polished slabs); King Arthur’s Hall, Tintagel (large insets in floor, Grade II), the front wall of West Hill Baptist Church, St Austell (cut stone). The most accessible example of a polished slab of Tremore Porphyry forms a large table top at the back of Lanlivery Church; some of the red tiles on the floor of the baptistery in St Austell Parish Church also are Tremore Porphyry.

A small quarry on a steep hillside about 1 km north of Lanivet (SX 034/653) in Bodwannick Wood exploits another east-west elvan associated with bands of calc-flinta. It was being worked in a small way for road metal at the time of Ussher’s survey but, he also suggests it was also used as a building stone:

’The rock is pale coloured, and has a fine matrix in which phenocrysts of quartz and feldspar are embedded. In (thin) sections it has the micaceous base referred to above (in the description of the elvans within the granite), and crystals of brown schorl in considerable number; blue crystals are rare. The larger crystals of orthoclase have within them a belt of microgranite suggesting a temporary cessation of growth, afterwards renewed when the material reached its present position. This feature is not uncommon in the other specimens.

Blocks of this rock occur in such numbers in the walls of the immediate neighbourhood as to suggest that it was once more extensively quarried, or else that it formed a large number of loose blocks before the ground was enclosed; the latter seems more probable, as the rock is well-known for its extreme hardness and durability when dried, and thus was likely to form many blocks at the surface.’

Watergate – Perranporth area

An elvan runs almost due north-south from Watergate Bay for 10 km to Carland Cross near Mitchell and has been extensively quarried along its length. No other elvan in Cornwall runs for such a distance in the anomalous N-S direction. At Watergate Bay the elvan is seen to be rather soft and decomposed and would not be suitable as a building stone.

However, a short distance to the south, at St. Columb Minor, there were several sizeable quarries. Reid & Scrivenor (1906) say that it is “extensively quarried” in this area and is about 40 feet thick. Three ‘old quarries’ are shown on the First Edition of the 1:2500 O.S. map (SW 841/623, 841/620 and 841/619) and three additional ‘quarries’ appear on the 1906 edition (SW 841/624, 841/621 and 840/618), so quarrying may well have continued into the early 20^th century. In view of the size and extent of these quarries this elvan must have been extensively used, probably as far afield as Newquay. Trerice Manor (Grade 1, N.T.) is built from elvan which may have come from these quarries. Modern housing now covers all except the southernmost quarry.

Reid & Scrivenor (op. cit.) say that the quarries yielded “a white or buff freestone which looks and works very like a sandstone. Above the water-level it is a buff freestone, easy to work, but not occurring in large blocks. Below the water-level it is greyer and in larger blocks, but as yet has been little quarried, for the various quarries are isolated and have no connected system of drainage. ”.

Flett’s petrographic description (in Reid & Scrivenor op. cit.) says “The rock is a quartz-felspar-porphyry, with pink orthoclase, in a micro-granitic matrix, and has a conspicuous chilled margin of finer grain. Under the microscope the central part of this elvan proves to be granophyric, having a groundmass entirely composed of coarse micropegmatite, a structure sufficiently uncommon in Cornish elvans to be worth remarking. In addition to the usual phenocrysts of idiomorphic perthitic orthoclase and corroded quartz, the latter filled with fluid cavities in the form of negative crystals, there is a small amount of weathered biotite and much muscovite. The white mica does not form well-shaped crystals, but occurs as clusters and tuft-like aggregates of small flakes which must be largely of secondary origin. Plagioclase and tourmaline are not represented in the microscopic slide, but apatite, zircon and iron oxides are all present. In the margin of the dyke the same porphyritic minerals occur, but in far smaller individuals, and the ground mass, which is very fine grained is beautifully micropoikolitic. The rest of the southern continuation of the Watergate elvan is dealt with as a separate entry.”

There are three small quarries marked on the 1:25,000 map on the line of the Watergate Bay elvan several km NE of Newlyn East (SW 842/5915, SW 846/577 and SW 850/558) which are said to be similar to the Watergate Bay elvan at St Columb Minor. These small quarries are closer to Trerice Manor, so could have supplied stone to it. The Watergate dyke disappears about 2 miles south-east of Newlyn East.

A small quarry is marked on the older 1:2500 maps a quarter of a mile east of Retyn (SW 889/585), no quarry is marked on the later maps. Flett et al. in Reid & Scrivenor (1906) say: ”(In hand specimen) …a coarsely crystalline mass of porphyritic crystals of feldspar, quartz, and occasional pinite, with unusually little groundmass; its chilled margin is finer-grained, with more groundmass. (Microscopically), the feldspar is microgranitic, consisting of quartz and feldspar, with scaly muscovite. The porphyritic feldspar is perthite and contains occasionally tourmaline and quartz. The phenocrysts of biotite are weathered to chlorite. Porphyritic muscovite occurs in the chilled marginal rock.” Also, in the building stone section Flett et al say: “At Retyn, however, this elvan (or perhaps a new elvan in nearly the same line) takes on a totally different character. It is a highly porphyritic rock, with crystals of quartz, orthoclase and tourmaline, and is quarried in large blocks. This quarry might yield a very handsome porphyry for polishing.”

On the west side of Cubert (SW 784/578) is a long linear quarry, following an east-west elvan. Reid & Scrivenor (1906) state that this porphyritic elvan is 25 feet wide and exceptionally sound and massive, in the chilled margin the ground mass consists principally of radiate micropegmatite. Housing now covers the site of the quarry. A long line of elvan extends some 4 km west of Newlyn East and there appears to have been some minor quarrying along its length at Cargoll and Trebellan, but no details are known.

The St. Agnes elvan passes close to the small St. Agnes and Cligga Head granite masses. However, as was the case with the elvans in and around the St. Austell granite, in the stretch of the elvan between St. Agnes Head and Perranporth it suffers to a greater or less degree from kaolinization and is unlikely to make a worthwhile building stone.

However, east of Perranporth there are several small quarries on what is assumed to be the continuation of the St.Agnes elvan. Just east of Wheal Hope there are two small quarries (SW 788/546) which appear to be on the line of the elvan and further east at Perran Coombe there is a linear quarry down the hillside (from SW 749/535 to SW 754/535, and small quarry in the opposite valley side (SW 755/535). The elvan is reported to hade 30^o south at this point. There is no information on the type or quality of the stone obtained from these small quarries on the St. Agnes elvan.

However, near Deerpark mine, 2 miles WSW of Newlyn East, there are two quarries on either side of the old mineral line (SW 807/552, quarry on east side of old railway line) which also appear to be on a continuation of the St. Agnes elvan and Flett et al describe them thus:

“Here again another aspect of the dyke is presented, for, in place of a chilled margin of the ordinary type, the edges show a beautiful flow structure, which results in a fine lamination, determined by the direction of flow. In the quarry on the west these planes lie parallel to the boundaries of the elvan and are straight, in that on the east the planes are curved, owing to the fact that here the elvan does not reach the surface of the ground above the quarry, and in consequence we see the spot where the flowing movement of the molten mass was arrested. At the edges only is the elvan porphyritic, in the centre it is of an even grain like that of a very fine microgranite. The rock is further remarkable for containing very little biotite. Along the planes marking the direction of flow there seems to have been some slight alteration of the original rock. In the quarry on the west of the rail the elvan is seen to be dipping at 35^o to the north; so that here the dip is reversed once more.”

A parallel elvan, runs just under 1 km north of the St Agnes elvan. It emerges from beneath the Perran Sands near Rose and continues north-eastwards towards Rejerrah. This is the granitic elvan of Perranporth, sometimes known as the Budnick elvan. This elvan is not marked on the latest edition off B.G.S. Sheet 346, but is marked on the 1906 edition and on the De la Beche 1838 revision of O.S. Sheet 96. In a quarry 250 yards east of Ponsmere Bridge (SW 763/543) Flett et al. say of the Perranporth granitic elvan:

“The mass of this dyke is perfectly homogeneous, and has the characters of a fine-grained granite. The orthoclase is white and sometimes porphyritic, but never markedly so. The biotite is quite fresh and the quartz has no crystal boundaries. A little tourmaline is probably present. Where the edge of the dyke can be observed, it is found to have the same appearance as a rather fine-grained quartz-porphyry, similar to the commoner type of these dykes”.

A series of small quarries and pits at Wheal Budnick mine are marked on the older editions of the 1:2500 map 1 mile ENE of Perranporth (Approx. SW 769/545) and the Perranporth granitic elvan is said to have also been quarried in the village of Rose. In the section on building stones Flett et al. say:

“A tough granitic elvan, quarried a mile north-east of Perranporth for road metal, is a handsome rock, and would be valuable if it could be obtained in blocks of sufficient size”.

This granitic elvan has possibly been used in early 19^th century building at St Piran’s Church at Perranzabuloe, around the window reveals in the interior and in the tower, etc. A Chapel at Rose may also have used this stone (Bristow, in Cole 2007).

There is a small quarry on the line of the elvan near Hendra farm (approx. SW 788/553), but no details are known.

Bodmin Moor and surroundings

Compared to the other granite masses, the Bodmin Moor granite and surrounding area do not have a conspicuous number of elvans and there are no elvans north of the A30, apart from a few small ones at De Lank quarry. Also, in common with the Carnmenellis granite, the only elvans to show evidence of kaolinization are those close to, or within, known china clay deposits. Those unaltered elvans within the granite are usually grey in colour and have been, in the past, mainly used for roadstone and not for building.

There are, however, two important elvans associated with the granite, in the Warleggan area and a long elvan stretching from Davidstow Moor to the Camel Estuary, which were important sources of stone for building. A further cluster of elvans are seen in the south-east corner of the granite and adjoining killas; however these are associated with metalliferous mineralization and/or weathering. Many small quarries and borrow pits exploited this altered material, which was soft enough to be excavated without the use of explosives and made an ideal material for general road maintenance before roads were sealed with tarmacadam. At best, this sort of material would only be suitable for Cornish hedges and rough farm buildings.

Note: For some unaccountable reason the elvans are not marked on the 1993 provisional edition of Sheet 337, but are marked on the 1912 edition by Reid et al.

In the currently active De Lank dimension stone quarry there are three elvan dykes crossing the southern part of the area occupied by the existing granite dimension stone quarry area (SX 010/753, SX 013/755, SX 011/754, SX011/751). The entrance road to the main quarry runs through a deep cutting which was excavated along the line of one of the elvan dykes. It has been reported that these elvans were mainly used as a source of aggregate.

Floyd et al. (1993) say “Immediately south of the northern working quarry at De Lank, two granite-porphyry dykes (‘elvans’) striking ENE-WSW, about 10m thick, are exposed in road cuttings and quarries on both sides of the river, and there is a third in a quarry on the south-west side. Much of the rock has been removed, but the chilled margins and faces at the ends are accessible and show the distinctive features of this rock which is fine-grained and often megacrystic.”.

Two small quarries exploited an elvan which crosses the A30 at Temple (west SX 134/735, east SX 139/734). If these are in the same elvan, then a dextral strike-slip fault along the line of the Warleggan river valley has displaced it by about 400m. The western quarry is now filled in and partly obliterated by road improvements, but the eastern quarry is open, but not worked. In between, along the line of the fault, is Temple china clay pit. Reid et al. (1910) report that the quarry shows numerous patches of fluorspar and some kaolinization, which probably means that it is unsuitable as a building stone. It was reported that it was mainly used as roadstone. An altered elvan which was formerly visible in Park china clay pit (SX 195/708) also showed a similar displacement by a dextral strike-slip fault.

Reid et al. (1910) also reports on a group of elvans on the south side of De Lank Water near its junction with the Camel (approximately SX 088/737) in Devonian slate. Reid reported that it was unusually fresh with macroscopic biotite and a few phenocrysts of quartz and feldspar. White mica was said to occur almost exclusively as minute fans which form part of the groundmass, and not as phenocrysts. The matrix showed beautiful granophyric texture, and was exceedingly fine-grained and spherulitic. The quarry is no longer visible.

A complex of east-west trending elvans was intruded into Devonian slates about 1 km south of the granite margin in the area around Warleggan and these have been used for building. The main quarry (SX 149/693, now disused, but accessible) lies 0.5 km south-west of Treveddoe mine and there are outcrops of similar elvan in woods to the south of the quarry and elsewhere in the Warleggan area. The elvan was said to be sill-like by Reid et al. (1910 and has abundant phenocrysts of feldspar and quartz, with occasional fluorite (usually as pseudomorphs) and tourmaline. A thin section indicates an estimated 40% of alkali feldspar, which means the elvan has not been greisened (see comments on greisening in the entry for Pentewan Stone). From a distance this elvan appears similar to Pentewan Stone in colour, but closer inspection shows phenocrysts of quartz and feldspar. Lack of greisening may indicate that this elvan will not be as durable as Pentewan Stone. St Barthlomew’s Church, Warleggan (Phillips 1999), only uses this elvan internally for the capitals above the granite columns. Other vernacular buildings in the village use this stone.

There are a number of other elvans in the area south and west of the granite which are reported by Reid et al. (1910), to be extremely altered, both by greisening and by tourmalinization/kaolinization and/or weathering. South of Caradon Hill they also report that on the sloping bank above Tremar (approx. SX 258/688) a hard elvan was formerly quarried for walling stone and several hard elvans were reported to have been encountered in mine workings and an underground railway tunnel. A hard elvan crosses Stowe’s Hill, near the Cheesewring and possibly continues in the killas as far as Rilla Mill; quarries marked on the 1:25,000 map 0.5 km south-west of Rilla Mill (SX 291/729) are probably in this elvan. There are also, as reported above, many small quarries in elvan in the area south-east of the granite, but most of these are altered and only suitable as borrow pit material for road making.

One of the longest elvans in Cornwall stretches discontinuously from Davidstow Moor for 25 km in an ESE direction as far as the Camel Estuary and has been quarried at many places along its length. Reid et al. (1910) reported:

“This stone supplied material for building the railway bridges between Wadebridge and Camelford, and is much employed for building chapels and halls”.

Many of the older buildings in St Kew and the surrounding country use St Kew elvan, including the Church (Grade 1, SX 015/768).

The principle exposure is in a long narrow quarry rather like a railway cutting alongside road 1 km west of St Kew. The main part is very overgrown with vegetation, but the western section (owned by the Cornwall Council) is still open, with a small face visible. Specimens show a rock which is unlike most other elvans, Reid et al. in the Padstow and Camelford Memoir (1910) say:

“In the hand-specimen the rock is light brown, often with green oval blotches, is fairly soft, and can be trimmed with an axe. Under the microscope it is seen to be allied to the minettes, but is usually decomposed and permeated by calcite; all the biotite is green with decomposition products arranged along the cleavage planes. Near St Kew globular inclusions of aplite, over a foot in diameter, are seen in the large quarries. At this locality the joint planes dividing the dyke are curved”.

It is clear that this elvan is rather different to many other elvans, it may be the result of the mixing of granitic and more basic magmas. This stone is rather drab greyish-green stone with joint faces showing brown oxide films. It is rather blocky and it does not look as if it would be at all easy to carve. It has been extensively used in St. Kew village and surrounding area, but probably the main use for stone from the quarry was for aggregate.

Further east, near the summit of Kit Hill, a relatively fresh elvan has been quarried, but whether this was for building stone or aggregate is not known. Reid et al. (1910) report that:

“the elvan is a compact, fine, quartz-porphyry, containing in addition to doubly terminated quartz crystals, porphyritic pink feldspar”. This elvan may continue eastwards to the Hingston Down granite where it is intensely altered and was worked in the Phoenix Brick Works (Ferguson & Thurlow 2005). A similar decomposed elvan was also worked by the Tamar Firebrick & Clay Company 4.5 km north-east of Callington (SX 400/717). There are several other brick works described by Ferguson and Thurlow in the Gunnislake area which are said to have worked decomposed elvans.

References

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