A Country Full of Holes TREVOR

The scientific naming and understanding of to infer the identity of belemnites as fossils relies on much the same methods of cephalopod molluscs; squid they were, thun- comparative morphology. Having seen the derbolts they are not. teeth of a modern shark, Steno was able cor- rectly to interpret tonguestones as the fossilized teeth of ancient sharks. Comparative morphol- Suggestions for futher reading ogy is, however, more difficult to apply if Bassett, M.G. 1982. ‘Formed Stones’, Folklore changes during fossilization profoundly alter the appearance of the organism (as in the case and Fossils. National Museum of Wales. Geo- of ‘horses heads’ (Fig. 6)), or if close modern logical Series No. 1, 32pp. (an invaluable analogues for the fossil do not exist. The latter source reference). is well illustrated by belemnites. No modern Zammit-Maempel, G. 1989. The Folklore of organisms have skeletons resembling the bul- Maltese Fossils, Papers in Mediterranean So- let-shaped guards of belemnites (Fig. 1) with cial Studies, Issue, 1, 29pp. (a detailed histori- their internal structure of radiating crystals of cal account of fossil myths and beliefs on this calcite. The crucial clue to the nature of Mediterranean island). belemnites was the discovery of the chambered phragmocone, constructed of aragonite and hence less often preserved, which fits into the Paul D. Taylor is head of the Invertebrates and conical alveolus of the guard. The Plants Division in the Department of phragmocone was sufficiently similar to the Palaeontology at The Natural History Museum, chambered shell of the modern squid Spirula London. for the 18th-century scientist Balthasar Erhardt A country full of holes TREVOR. D. FORD Mining voids exist throughout Britain n recent years, there have been several inci- (Fig. 2). An articulated lorry had one of its Idents arising from the presence of unstable wheels caught in a collapsed sandstone ‘cavern’ old mine workings in parts of England where beneath a Nottingham street (Fig. 3). A back few residents had any memory of anything ever garden in Cornwall disappeared into an unsus- being mined. As examples, a bus fell into an old pected mine shaft. Several million pounds have chalk mine under a street in Norwich (Fig. 1) been spent filling in old limestone mines in the and part of a housing estate in Bury St West Midlands after a series of collapses, one in Edmunds fell into old chalk-mine workings the middle of a football pitch in Dudley! An- Fig. 1. Collapse of old chalk mines in Norwich, 1988. (Photo reproduced with permission of Eastern Counties Newspapers.) © Blackwell Science Ltd, GEOLOGY TODAY, July–August 1998/145 Gdjul3.p65 145 12/11/98, 15:02 Fig. 2. (left) Crown holes over old chalk mines in Bury St Edmunds, due to liquefaction of chalk by leaking drains. (Photo: Tony Waltham.) Fig. 3. (below left) Crown-hole failure of sandstone under a passing lorry. A leaking drain weakened the roof over an old wine cellar in Nottingham. (Photo: Tony Waltham.) and, in spite of the efforts of National Coal Board geologists, many older workings are un- charted. Some 4000 shafts were plotted during the development of the new city of Telford on top of the Coalbrookdale Coalfield. Less well known are the mines, mainly in the Yorkshire coalfield, which have worked products such as ganister and fireclay for refractory purposes. Other materials worked in some coalfields in- clude building stones, usually quarried but oc- casionally mined. Also, near Pontefract and Castleford there are several kilometres of mine workings only a few metres beneath the surface from which the basal Permian sands have been extracted for glass-making. Coal mining deep beneath these has increased the possibility of subsidence. Several coalfields have also had ironstone mines, where either shales packed with nodules or bedded ironstones were raised. Metal mining Britain also has its well-known lead, tin, zinc and copper mining fields which have worked vein deposits in Cornwall and Devon, the Mendip Hills, the Peak District, Shropshire, the North Pennines, the Lake District, Angle- sey and in mid and North Wales. Less well other incident occurred when a recently com- pleted semi-detached house started to collapse at one end of a housing estate near Pontefract while the builder was still erecting houses at the other end, on top of unsuspected old mine workings! By mines, I mean underground workings. Quarries and opencast pits are another story. A quick tour will perhaps open your eyes to what has been mined in the past and thus to where the dangers of instability are greatest. Old coal mines The presence of old coal-mine workings is an obvious fact of life in the coalfields, and subsidence is only to be expected during extraction (Fig. 4). Once mining has ceased, subsidence damage may decline, but sometimes it is aggra- vated by water movements in the old workings. Fig. 4. Subsidence of the Crooked House due to coal mining at Himley, All our coalfields are affected to varying extent Staffordshire. (Photo: Tony Waltham.) 146/© Blackwell Science Ltd, GEOLOGY TODAY, July–August 1998 Gdjul3.p65 146 12/11/98, 15:02 known are the gold deposits of Dolgellau and the wolfram mines of Carrock Fell. Most of the minerals occur in fissure veins so that workings are more or less vertical. Estimates of the number of shafts vary, but a figure of 50 000 in the Peak District is a fair estimate and equiva- lent numbers are probably present in the other metal-mining fields. Waste was often stacked on stone or wooden stemples in mined-out veins (Fig. 5). Lines of shafts mark many veins, and occasional collapses leave irregular gashes on hillsides. Prehistoric workings for copper ore have recently been identified on the Great Orme at Llandudno, at Cwmystwyth in central Wales and at Ecton in Staffordshire. Apart from lead and zinc ores, fluorspar and baryte are still being worked in some of the old Pen- nine lead-mining areas. Even the common mineral calcite is still worked from veins in the Peak District for stucco, terrazo and other or- Fig. 6. Crown-hole and even fewer have been surveyed. Ironstone namental purposes. Spectacular collapses have subsidences over old nodules have been worked from shale beds in taken place over quite recent ‘spar’ workings in ironstone workings at several coalfields, particularly in Derbyshire Derbyshire. Holwell near Melton and Coalbrookdale. Secondary iron ores have Mowbray, been mined from replacement deposits in the Leicestershire. (Photo: Tony Waltham.) Carboniferous Limestone flanking the Lake District, the Forest of Dean and at Llanharry near Cardiff. Earthy iron ores have been extracted as ‘raddle’ used for pigments at several localities. Chalk mines The East Anglian counties and several parts of Southern England have all had chalk mines; but why on earth mine chalk when there are large areas of the Downs entirely composed of chalk and easily accessible? Quite simply, with bulk transport being difficult and costly in ancient times, it was cheaper to raise chalk from below your own estate for use as a fertilizer spread on top of superficial deposits which were deficient in lime. At Bury St Edmunds, Fig. 5. Waste rocks ancient chalk mines beneath a housing estate stacked on stone became unstable when leaking drains softened stemples in an old lead the chalk (Fig. 2). Apart from Norfolk and Suf- mine, Via Gellia, folk, chalk has been mined from the ‘dene Derbyshire. (Photo: T. holes’ of Essex and Kent, from galleries near D.Ford.) Reading, Berkshire, and in Buckinghamshire and Hertfordshire. One chalk mine at Chislehurst in Kent has been opened as a tour- Ironstone mines ist attraction. Some chalk, as at Beer in East Bedded ironstones were worked in the Jurassic Devon, was mined as a building stone. rocks of North Yorkshire, Lincolnshire, Leices- tershire, Northamptonshire and Oxfordshire Gypsum, salt and other evaporites until some 30 years ago. Extensive networks of almost horizontal galleries lie at no great depth Gypsum for making plaster has long been in all these areas and crown-hole collapses are mined from the Triassic strata of Yorkshire, fairly common (Fig. 6). Ironstones of early Nottinghamshire, Leicestershire, Derbyshire Cretaceous age were the basis of an ancient and Staffordshire. Some of these areas have iron-making industry in the Weald of Kent and yielded alabaster for ornamental and tomb- Sussex, but few of the workings are accessible stone use. Recent road construction ran into © Blackwell Science Ltd, GEOLOGY TODAY, July–August 1998/147 Gdjul3.p65 147 12/11/98, 15:03 problems with unsuspected cavities in the gypsum beds south of Derby. There are also extensive gypsum/anhydrite mines at Billingham on Teeside, at Sherburn-in-Elmet, East York- shire, and in the Vale of Eden in Cumbria. Gypsum has also been raised from Lower Cre- taceous strata in the Weald of Sussex. Salt is mined or pumped as brine from the Trias in Cheshire and adjacent parts of North Stafford- shire, often with extensive collapses. Potash salts are raised from the Permian evaporites near Whitby in north-east Yorkshire, but the great depth of the workings has not led to any surface problems as yet. Building stones Various building stones have been mined too. Sandstones have been exploited underground in several places in the Pennines and in Staf- Fig. 8. A pillar fordshire. Perhaps the best-known building- and others for sand to spread on floors before supporting the roof (?) the days of carpets (Fig. 9). Over 400 of these stone mines are those which worked the in a Hearthstone Mine Inferior Oolite around Bath and Corsham artificial sandstone ‘caves’ have been charted at Godstone, Surrey.

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