The burning of the limestone

The piece which I posted last week from the Transactions of the Bristol & Gloucestershire Archaeological Society avers that there is no adequate explanation for the reddening of burnt oolitic limestone.  But that was published in 1925 and refers to the reddening of the limestone being mentioned in 1818 in the Transactions of the Society of Antiquaries.  An excellent explanation does, of course,  appear in "Crickley Hill: the Hillfort Defences" (Dixon 1994), in the geological chapter by R J Firman:

"An understanding of the mineralogical changes brought induced by heating limestone is thus of crucial importance in interpreting the archaeological evidence.  The most obvious indication of heating is the development of a brick red colour due to the dehydration of rust coloured ferric hydroxides leading to the formation of haematite.  It is important to note that the intensity of the red colour is unrelated to the intensity of the heating, being directly proportional to the concentration of ferric hydroxide, 'limonite', minerals in the original unburnt limestone. Moreover, in a conflagration, conditions may be sufficiently reducing, to preclude the formation of haematite: magnetite or less stable ferrous compounds forming instead.  These, when weathered, impart a grey or brownish yellow colour to the burnt limestones. Given a strong draught, limestone will calcine at temperatures of 800 to 900°C and, in still conditions 1050°C.  Masses of 'meringue-like' material in the prehistoric earthworks show that such calcination did occur, the resulting quicklime having reacted with water to form slaked lime, and this in turn wholly or partly, becoming carbonated as it reacted with atmospheric carbon dioxide.  Reddening and calcination are thus good indicators of burning and destruction by fire.  They must, however, be interpreted cautiously, because some of the red colour, particularly if associated with clays and sands, could be glacially derived from naturally released Triassic sediments."

Excavations on Leckhampton Hill 1925

Thanks are due to the Secretary of the Bristol & Gloucestershire Archaeological Society for permission to reproduce extracts from the BGAS's Transactions.  Here a couple of intriguing items from 1925.

"Less than a mile away are three barrows, one a particularly fine long barrow of the Neolithic Age, at "the Crippets", two round barrows near the inn known as the "Air Balloon", and by the side of the road to Birdlip, was found a beautiful mirror enamelled in colours, at  a burial place of the Iron Age, one of the most striking specimens ever discovered of that period, now in Gloucester Museum.  Hence there was sufficient reason to welcome the opportunity of exploring and dating the tumulus and the adjoining camp.  

A particularly interesting feature of the core of Leckhampton Camp is the appearance of the action of fire or intense hear, which has reddened the yellow oolite rock in a remarkable way.  This peculiarity is not confined to Leckhampton Camp - for it is very noticeable at Crickley Camp - two miles away.  

Thomas Lloyd Baker, in a paper read before the Society of Antiquaries, London in 1818, refers to this fact for which there is no adequate explanation."

A much coveted oolitic limestone trophy ...

Dr Phillpotts's 1980 caption reads: "Julian Parker looks on as John Parry presents the piece of limestone to Mike Taylor as Personality of the Year".  Hmm... well I suppose it made sense to make trophies out of limestone, as it wasn't exactly in short supply.   

There are some details in this shot that bring back certain memories.  Not only do I still appear to have some hair to go with the beard in this photograph, but I am wearing evening dress: the wing collar and the bow-tie can just about be made out.  I now recall buying the dinner jacket, and other necessary items, at the Cheltenham Oxfam Shop.  I rather think I was accompanied by Jane Dineen or Ros Cleal, or both, on this particular shopping expedition. We swapped a pair of trousers, that were obviously far too big for me, from one hanger, which bore a jacket that fitted me, for the trousers belonging to an entirely different suit, which had a jacket that was far too small for me.  The resulting ensemble, plus dress shirt and bow-tie was acquired for £5.  I can only hope that a strangely-shaped customer with narrow shoulders, pigeon chest and an enormous waist came along and bought the curious combination dinner suit that was left behind after this feat of leger-de-main.

Mike Taylor, even indoors, is wearing his astonishingly long knitted scarf, a better view of which, on site, is to be found in the top photo here.  Mr Parry, meanwhile, is sporting a black shirt with extravagant cuffs and pearl buttons gleaming in the dim light.  I expect it was one of those evenings when John, with a broad grin, verging on a leer, had announced "I'm going to make myself pretty!".

Behind us is the ill-fated and long-suffering Ullenwood piano. Its debilitated state is hinted at by one or two keys that lie depressed unable to spring back into position.  The piano sustained ever greater damage down the years and, I see, from examining Dr Phillpotts's definitive history of the Below Average White Band, that it never featured as an instrument after the 1980 season.

But what I really want to know is why there are two bottles of GL cider, on top of the piano, conjoined by a pair of underpants or knickers, which bears what looks suspiciously like a representation of Donald Duck on the front ...

Richard Savage's Prologue 1988

My thanks again to Richard Savage and the Crickley Hill Trust for permission to reproduce material from Richard's 1988 booklet "Crickley Hill: Village, Fortress, Shrine". If you click on the images they will enlarge, but for ease of reading I reproduce the text below.

"Between 210 and 135 million years ago, much of the area which is now Britain was covered by ancient seas.  In their warm waters were deposited the clays, sands and limestones that make up the Cotswolds we see today.  The plants and animals living in them are preserved as fossils in the rocks of the period, known as the Jurassic, which stretch obliquely across England from Dorset to Yorkshire.  The hard limestones end in a scarp on their western side which drops abruptly for several hundred metres to the valleys.  These rocks were lifted from the seabed by earth movements which also tilted them so that in the Cotswolds they sloped gently downwards towards the southeast.

Crickley Hill is a promontory of the Cotswold scarp, 8 km from Gloucester and 5 km from Cheltenham.  The nature of the limestone uplands has had a profound influence on the use of the hill in ancient times and our approach to studying it.  The Stone ("oolite") is permeable to water, providing a light well-drained soil with clear springs issuing at a lower level - 60 m below the summit of Crickley - where the limestone meets impermeable clay.  Much of the stone, especially that near the surface, splits easily into pieces of the size and shape suitable for building.  Post holes and stake holes can be made in it with simple tools, though the rock is hard enough to discourage casual digging.  It is easily and permanently discoloured by fire, and at high temperature (900 - 1,000°C) turns to quicklime, which, when slaked, forms a powdery mortar-like aggregation.  The Crickley stone is not of the best quality, so there has been only local demand for it as building stone, though it has been burned for line and used as road stone.  Accordingly the damage to the promontory by quarrying has been limited; it has removed several metres from the south side, and made both sides steeper.  They were always steep enough to make ascent troublesome and to prolong a climber's exposure to observation from above. (Illustration: Exposure of oolitic limestone in the Crickley Hill quarry)

Within 25 km of Crickley more than a dozen hill-forts take advantage of similar conditions.

Flint, on which everyday technology depended in Britain until after 2000 BC, does not occur in limestone, though small pieces of poor quality may be found in gravel deposits.  In this, the inhabitants of Crickley and their neighbours could never be self-sufficient, and they had to obtain supplies from areas of chalk to the south and east, none nearer than 50 kms away.  All flint found on the hill was brought by man.  

A natural hollow, 100m long and 25 m wide, runs beside the southern edge of the hill at its western end.  It represents a fissure in the rock which it will eventually break the mass to the south of it away into the valley, but it has been stable for at least 6000 years, since the neolithic period. The limestone along its bottom and has degraded to a matrix of small particles which is easy to dig into.  The traces of neolithic houses the best preserved here, where substantial postholes could most easily be made with the tools of time, and here, too, we can follow the small grooves and stake holes intended for wattle fencing. (Illustration: Typical fossils of the Crickley Oolite)

The soil on the hill is shallow, seldom exceeding 15 cms thick. Because of this the stratigraphy - the sequence of deposited layers which can be distinguished from one another and analysed to establish a succession of events - is severely limited.  There are substantial accumulations only in such large features as ditches and quarry pits, and not always there.  On the other hand, all but the most trivial ground-work has always had to affect the bedrock, in which its traces are usually permanent and unmistakable.

Since the stone resists erosion fairly well, and even the normal methods of building "drystone" (mortarless) walls make surprisingly durable structures, we can usually recognize even slight remains of walling, the residues of ancient demolition.  It is a feature of the site that the prehistoric walls have not been much robbed of their stone in recent centuries. Unofrtunately the Crickley soil preserves seeds, pollen, and other organic remains only when they have been carbonised by heat, and not always then.  On the other hand, it preserves snail shells very well indeed.  These can often be used as evidence of the nature of the environment during the snails' lifetime at the places where they are found; species can be identified which prefer grassland, for example, or shady woodland.  It also preserves bone, when this has been buried, and thus protected, in pits and ditches.

Crickley Hill may have had a key position in the prehistoric geography of the region, offering a near approach of the Cotswold upland to the lowest part of the Severn at which it could be crossed into Wales without much difficulty, perhaps on the northern side of Gloucester.  The hill has easy access eastwards to the Thames Valley and south-east Britain while any trade with running from south-west to north-east along the high ground of the limestone scarp must have passed close to it.  It is tempting to speculate that Crickley may have stood near, and at some periods on, a cross roads, where apart from the river crossing in the Vale reached the uplands and divided into north, south and eastward routes, and this was recurrent motif in its long story. (Illustration: Prehistoric use of oolite. The wall of the second hillfort"

Oolites for Obama in Food Orgy ...

A friend with whom I was lunching on Sunday suggested that if I wished to attract readers to the blog I should see what happened if I associated Obama, food and sex in the title of the post.  So I'm sorry to disappoint anyone who's reading this because they thought it might be salacious.  If you are reading this and wondering what an oolite is: the answer is here.

To return to the food theme and the edibile appearance limestone can sometimes assume, here's Dr Ferris: "It would appear that Crickley Hill Man's appetite for meringue and chipples is of a similar order to his legendary love of banana custard. However, this will be my last posting on the subject, as I have now found the origin of the term 'meringue' in Phil's 'Crickley Hill: The Hillfort Defences.' I'm not sure how I missed it previously. On page 47 Phil describes 'a large area of very hard white concreted limestone. Its consistency and appearance was exactly caught by the nickname immediately applied to it in compliment to our then chef, Tony Watts, renowned for his robust cooking: for the past two-and-a-half decades this immensely hard material has always been called 'MERINGUE'.'

 

Should Crickley Hill Man ever find himself tempted to raid his capacious fridge some time for a midnight snack, he might better turn to page 52 of 'Crickley Hill' and peruse Figure III.40 where he will see a thick deposit of 'meringue with grey burnt stones' temptingly topped off with a generous cholesterol-free spread of 'dark humus with chipples.' Altogether fewer calories and more intellectual stimulation there."

Shouldn't that read houmous with chips?

Synonyms for oolites ...

Iain Ferris muses: "I was interested to note that in Crickley Hill Man's recent posting on the geological background of the site the origins and meaning of the word 'gull' were explained. This was one of many esoteric words unique to the vocabulary of all those digging on the hill and made me remember two other, less precise terms used to describe deposits and fills. The gulls were usually backfilled with a deposit formed of often-loose tiny pellets of rounded limestone-a dozen or so of which would comfortably just cover the area of a fingernail-which we all called 'chipples'. These also occurred in small numbers in other features. The presence of chipples often also was an indicator that you were getting towards the true edge of a posthole during its excavation. Sometimes the sides of gulls were formed by a type of yellow-grey, decayed, spongy limestone concretion-presumably again resulting from water erosion and redeposition-that was known generally as 'meringue'. Do these terms ring any bells with Crickley Hill Man and his dedicated readers?"

I was just humming and hahing over what to write this morning when Iain saved me the trouble by sending in these observations: I certainly remember all three words, 'gull', 'chipple' and 'meringue' being employed.   

I've found a passage in 'Fundamentals of Biogeography' by Richard Huggett (Routledge 2003) "Many cliffs are dissected by wide vertical joints that form open clefts or passageways. In Britain such widened joints are called gulls or wents which are terms used by quarrymen." 

I am not an etymologist, but wonder whether the genesis of 'gull' is a simple shortening of gully to express a related physical manifestation. Comfort for this suggestion may come from Volume XCIX of the Quarterly Journal of the Geological Society of London 1944: "The word 'gull' is an old term meaning chasm or gully and it has long been applied by quarrymen to widened fissures". Also, from the proceedings of the Dorset Natural History and Archaeological Society 1942: "Fitton recorded that the solution fissures in the Portland stone as Hazeley in Oxfordshire were called 'gulls' by the quarrymen (1836, Trans. Geol. Soc. (2) iv, 276)."

Chipples appears to be uniquely used at Crickley in a geological context: in a less elevated tone than what is written above on gulls, the word appears in the Urban Dictionary to mean chocolate covered nipples - I am not making this up - and bizarrely, in another food related use in a string starting with someone suggesting that it is a term used, for, of all things, spring onions (presumably a diminutive of the Italian for onions 'cipolle', thence 'cipolline').  Lastly, some people seem to use the word for diminutive chips of the French fry variety. Hmm. Curious and unwelcome visions begin to appear in Crickley Hill Man's mind.

Meringue seems straightforward by comparison, I am delighted to say, and comes from the close resemblance of the concretion of dissolved rock to the food.

Geology

By kind permission of Professor Dixon: the geology section of "Crickley Hill and Gloucestershire Prehistory":

"The Cotswold Hills are part of a ridge of Middle Jurassic rocks, mainly limestones, that runs diagonally across England from Dorset to N.Yorkshire. The south-easterly tilt of the limestone strata produces a gentle slope towards Oxford and a steep scarp towards the Vale of Gloucester, from which project a number of spurs or headlands. Crickley Hill, pointing diagonally from the scarp edge, towards the west, is one of these. Its sides have been steepened, and its promontory-like shape accentuated, by the quarrying, over centuries, of the oolitic limestone of which it is formed. This rock, so named because it is composed of spherical grains of calcium carbonate resembling fish roe (Greek oion: an egg; lithos: a stone), can produced excellent building stone, formerly transported to areas outside the Cotswolds for use in prestigious buildings. Crickley's stone, however, is of poorer quality, and its use has been local: for the surviving prehistoric structures on the site, and recently for houses, field walls, and, after burning it, to improve the clays of the lowlands; the hill's most recently worked quarry closed only in 1963. Archaeologically, the effect of the quarrying has been most drastic on the southside, now cliff-like in profile, where part of the hillfort rampart and interior has been removed; the original extent can thus no longer be determined.

Although massive below, as may be seen in the recent quarry, the oolite near the surface on the hilltop has been horizontally laminated by exposure. In undisturbed areas, once the topsoil has been removed, the rock looks like great expanses of crazy paving, in which postholes and other man-made features are clearly visible. Many places, however, have been disturbed, not only by rabbit holes and tree roots, but also by geological phenomena. Along the axis of the promontory run large fissures of great depth. Originally vertical joints in the limestone, these had been enlarged to their present surface width of up to 20 feet by seeping water, which dissolves calcium carbonate, and by frost, and they are packed with the tiny fragments of the once solid rock thus destroyed. Known to quarrymen as "gulls", these fissures can be archaeologically confusing: not only do they sometimes superficially resemble back-filled ditches, but real features occurring in them can be less well-defined than the flat-bedded limestone; in them also, because of their softer matrix, are found most of the rabbit holes. In a least one instance the first Neolithic builders to took advantage of their softness and aligned a stretch of their causewayed ditch along the gull. On excavation the ditch was found to have no bottom, but instead a deep fissure, formed along the existing line of weakness only after the ditch was at least partially refilled.

In addition to the main axial fissure other cracks run along and parallel to the side of the hill. These demonstrate clearly the forces of erosion at work, by infinitesimal stages detaching blocks of rock from the slope, so that, over the millennia, the entire scarp recedes, leaving occasional residual masses of harder rock, such as Robins Wood Hill and Churchdown Hill, both of which can be seen from Crickley."

© Crickley Hill Trust, 1977.

The entrance of the 2nd hillfort under excavation in 1970

By permission of Philip Dixon, the back cover photograph from "Crickley Hill and Gloucestershire Prehistory". Impressive stonework. Many, many oolites (derived from Greek oion liqoV, meaning egg stone because of the resemblance to fish roe). © Crickley Hill Trust 1977

Half a posthole: F4264 Crickley Hill 1980

 

Posthole F4264 exactly half dug during the 1980 season. It's easy to see from the undug section why it was not too difficult to spot the feature because of the obvious differentiation of the fill from the surrounding surface. The upended packing stones round the edge of the fill as compared to the flat jigsaw of the surrounding rock are the giveaway.

Cutting B6 porch posthole

Serious posthole on Cutting B6, August 1979, feature number not known by me. Shame no scale in sight, but I do remember this being an exceptionally large one. Must have been hard work hacking through the oolites to make this.

Rocks (specially for Lucy Loveridge) ...

How do we describe those rocks? Well this is what the British Geological Survey have to say:

"Pale grey to yellowish brown limestones; lower part dominated by medium- to coarse-grained ooidal shell-fragmental grainstone ('Lower Limestone'), passing up into rubbly, poorly sorted, shelly, shell-detrital, moderately to highly pisoidal grainstones and packstones ('Pea Grit') with thin marl beds. South of Painswick, the succession is apparently replaced by ooidal grainstones comprising the Frocester Hill Oolite and Selsey Hill Oolite of Mudge, D C, 1978a, but the relationship between these strata and the type Crickley Member is uncertain."

For more enlightenment, Rocks is the place...