52-440: The Aubrey holes are a ring of 56 chalk pits at Stonehenge , named after seventeenth-century antiquarian John Aubrey . They date to the earliest phases of Stonehenge in the late fourth and early third millennium BC . Despite decades of argument and analysis, their purpose is still unknown, although an astronomical role has often been suggested. Whilst visiting the monument in 1666, Aubrey noticed five circular cavities in
104-463: A 1981 article in Nature pointed out that the holes had been backfilled thousands of years before Aubrey visited the site. The presence of later cremation burials and sarsen stone chips in the holes' upper fills supports this. That none of the other antiquarians who visited the site noticed any such holes implies that they were not permanent features either. Pitts argues that they were more likely to be
156-423: A few are more recent. A mixture of chalk and mercury can be used as fingerprint powder . However, because of the toxicity of the mercury, the use of such mixtures for fingerprinting was abandoned in 1967. Heelstone 51°10′45″N 1°49′31″W / 51.179305°N 1.825302°W / 51.179305; -1.825302 The Heel Stone is a single large block of sarsen stone standing within
208-642: Is mined from chalk deposits both above ground and underground . Chalk mining boomed during the Industrial Revolution , due to the need for chalk products such as quicklime and bricks . Most people first encounter chalk in school where it refers to blackboard chalk , which was originally made of mineral chalk, since it readily crumbles and leaves particles that stick loosely to rough surfaces, allowing it to make writing that can be readily erased. Blackboard chalk manufacturers now may use mineral chalk, other mineral sources of calcium carbonate, or
260-610: Is a fine-textured, earthy type of limestone distinguished by its light colour, softness, and high porosity. It is composed mostly of tiny fragments of the calcite shells or skeletons of plankton , such as foraminifera or coccolithophores . These fragments mostly take the form of calcite plates ranging from 0.5 to 4 microns in size, though about 10% to 25% of a typical chalk is composed of fragments that are 10 to 100 microns in size. The larger fragments include intact plankton skeletons and skeletal fragments of larger organisms, such as molluscs , echinoderms , or bryozoans . Chalk
312-404: Is a soft, white, porous , sedimentary carbonate rock . It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor . Chalk is common throughout Western Europe , where deposits underlie parts of France, and steep cliffs are often seen where they meet the sea in places such as
364-508: Is also the only form of limestone that commonly shows signs of compaction. Flint (a type of chert ) is very common as bands parallel to the bedding or as nodules in seams , or linings to fractures , embedded in chalk. It is probably derived from sponge spicules or other siliceous organisms as water is expelled upwards during compaction. Flint is often deposited around larger fossils such as Echinoidea which may be silicified (i.e. replaced molecule by molecule by flint). Chalk
416-428: Is applied to the hands and feet to remove perspiration and reduce slipping. Chalk may also be used as a house construction material instead of brick or wattle and daub : quarried chalk was cut into blocks and used as ashlar , or loose chalk was rammed into blocks and laid in mortar. There are still houses standing which have been constructed using chalk as the main building material. Most are pre- Victorian though
468-403: Is around 5m inside the monument's bank. 21 of the holes remain unexcavated and no reliable dating material has been recovered from the other 35. The only available carbon date from the holes comes from charcoal in one of the later cremations. It gives the broad range of 2919–1519 BC. That sarsen stone chips have only been found in the upper fills of the excavated pits implies that the digging of
520-518: Is commonly used as a drying agent to obtain better grip by gymnasts and rock climbers. Glazing putty mainly contains chalk as a filler in linseed oil . Chalk and other forms of limestone may be used for their properties as a base . Chalk is a source of quicklime by thermal decomposition , or slaked lime following quenching of quicklime with water. In agriculture , chalk is used for raising pH in soils with high acidity . Small doses of chalk can also be used as an antacid . Additionally,
572-505: Is not a whole number and so it cannot be used to predict an eclipse without precision equipment, using only crude marker stones or timber posts in a circle instead. Hawkins' theory was that three 18.61 year cycles multiply out to 55.83, which is much closer to an integer and therefore easier to mark using 56 holes. Hawkins argued that the Aubrey Holes were used to keep track of this long time period and could accurately predict
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#1732771993430624-606: Is now established that the different features at the monument that he tried to incorporate into many of his alignment theories were in use at different times and could not have worked alone, the lateness of the installation of the Heel Stone being the final nail in the coffin. Furthermore, the 56-year period is not in fact a reliable method of predicting eclipses and it is now accepted that they never repeat their date and position over three consecutive 18.61 year-long lunar cycles. Hawkins' theories also required strict observance of
676-582: Is now usually made of talc (magnesium silicate). Chalk beds form important petroleum reservoirs in the North Sea and along the Gulf Coast of North America. In southeast England, deneholes are a notable example of ancient chalk pits. Such bell pits may also mark the sites of ancient flint mines, where the prime object was to remove flint nodules for stone tool manufacture. The surface remains at Cissbury are one such example, but perhaps
728-604: Is so common in Cretaceous marine beds that the Cretaceous Period was named for these deposits. The name Cretaceous was derived from Latin creta , meaning chalk . Some deposits of chalk were formed after the Cretaceous. The Chalk Group is a European stratigraphic unit deposited during the late Cretaceous Period. It forms the famous White Cliffs of Dover in Kent , England, as well as their counterparts of
780-451: Is that they were excavated in turn in some unknown ritual involving a procession around the inside of the monument. Others have pointed out the significance of the 28-day human menstrual cycle and argued that the holes may have been fertility indicators. Alexander Thom calculated that the circle of holes had been laid out in a circumference of 131 of his megalithic rods although this number has no known significance. A recent CAD study of
832-401: Is typically almost pure calcite, CaCO 3 , with just 2% to 4% of other minerals. These are usually quartz and clay minerals , though collophane (cryptocrystalline apatite , a phosphate mineral) is also sometimes present, as nodules or as small pellets interpreted as fecal pellets. In some chalk beds, the calcite has been converted to dolomite , CaMg(CO 3 ) 2 , and in a few cases
884-495: Is unclear, although parallels were drawn with Native American totem poles by Stuart Piggott in a 1946 BBC radio lecture. A 50 cm high carved wooden figure found in the Thames Marshes in 1912 and carbon dated to 2460–1980 BC has been used rather tenuously to support the theory of carved wooden posts serving a more terrestrial purpose. Another possible explanation for the holes, suggested by Richard Atkinson,
936-595: The Avenue outside the entrance of the Stonehenge earthwork in Wiltshire , England. In section it is sub-rectangular, with a minimum thickness of 2.4 metres (7 ft 10 in), rising to a tapered top about 4.7 metres (15 ft) high. Excavation has shown that a further 1.2 metres (3 ft 11 in) is buried in the ground. It is 77.4 metres (254 ft) from the centre of Stonehenge circle. It leans towards
988-752: The Cap Blanc Nez on the other side of the Dover Strait . The Champagne region of France is mostly underlain by chalk deposits, which contain artificial caves used for wine storage . Some of the highest chalk cliffs in the world occur at Jasmund National Park in Germany and at Møns Klint in Denmark . Chalk deposits are also found in Cretaceous beds on other continents, such as the Austin Chalk , Selma Group , and Niobrara Formations of
1040-536: The Dover cliffs on the Kent coast of the English Channel . Chalk is mined for use in industry, such as for quicklime , bricks and builder's putty , and in agriculture , for raising pH in soils with high acidity . It is also used for " blackboard chalk " for writing and drawing on various types of surfaces, although these can also be manufactured from other carbonate-based minerals, or gypsum . Chalk
1092-472: The phases of the moon which further complicated predictions using his model. In 1966 Sir Fred Hoyle examined the arguments in favour of an astronomical purpose for the holes and concluded that the 28 day lunar cycle could still have been indicated by moving a marker stone representing the moon anticlockwise by two holes every day, ending up with 56 holes in total. By moving another marker anticlockwise two holes every 13 days, which represented
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#17327719934301144-563: The 1935 reburial was uncovered at the site. The project was detailed in an episode of the PBS TV series Nova around the same time. Many interpretations prefer an astronomical explanation for the purpose of the holes although this is by no means proved. It was formerly thought that when the Aubrey holes were first dug, the only standing feature at Stonehenge was the Heelstone , which marked
1196-466: The 1960s. An early attempt to analyse the positions of the Aubrey holes was undertaken by Gerald Hawkins , a professor of astronomy at Boston University in the 1960s, using an IBM 7090 computer. In his book Stonehenge Decoded , Hawkins argued that the various features at the Stonehenge monument were arranged in such a way to predict a variety of astronomical events. He believed that the key to
1248-607: The Moon during lunar eclipses. Plutarch further records that the Pythagoreans symbolically associated Typhon with a polygon of 56 sides, hence the connection of 56 to lunar eclipses is explicit, at least for the Hellenistic era. Although less complex and romantic than Hawkins' 'Stone Age calculator' such a technique is certainly feasible if only in theory. Much more elaborate predictive practices have also been suggested for
1300-732: The North American interior. Chalk is also found in western Egypt (Khoman Formation) and western Australia ( Miria Formation ). Chalk of Oligocene to Neogene age has been found in drill cores of rock under the Pacific Ocean at Stewart Arch in the Solomon Islands . There are layers of chalk, containing Globorotalia , in the Nicosia Formation of Cyprus , which formed during the Pliocene . Chalk
1352-474: The Sun, an annual journey around the circle could also be made. Two further marker stones would also have had to be moved round 3 holes per year to represent the points where the moon (or rather its marker) crossed the Sun marker's path. Hoyle proved that this could have been used to produce a much more reliable method of predicting eclipses as whenever the moon and sun markers are directly opposite each other and
1404-540: The archaeologists to suggest that the 56 holes had held Welsh bluestones , since they are too shallow to be postholes. In fact the holes are identical in width, depth, and shape to the bluestones located elsewhere in Stonehenge. They are confident that the Aubrey holes belong to Stonehenge's initial phase of construction. Professor Parker Pearson said: "It's very exciting that we have evidence for stones right from its beginnings around 3000 BC. That's almost 500 years earlier than anyone had thought." The astronomical readings of
1456-460: The astronomical significance of the number of the Aubrey Holes and their circular arrangement and tends to suggest that any astronomical purpose for the site may have been no more than symbolic. According to the astrologers Bruno and Louise Huber the Aubrey holes were an astronomical abacus to mark the positions and calculate the movement of lunar nodes . Mike Pitts has asserted that the Aubrey Holes did in fact originally hold timbers and compares
1508-454: The cavities left by features that had recently been removed. He has suggested that perhaps further megaliths stood at Stonehenge which occupied these other holes and are now lost. 25 of the holes were excavated by Hawley in 1920 and seven more in 1924. In 1950 Stuart Piggott and Richard Atkinson dug two more Aubrey Holes which brought the total excavated to 35, including one that Richard Colt Hoare may have encountered whilst digging beneath
1560-548: The chalk came mostly form low-magnesium calcite skeletons, so the sediments were already in the form of highly stable low-magnesium calcite when deposited. This is in contrast with most other limestones, which formed from high-magnesium calcite or aragonite that rapidly converted to the more stable low-magnesium calcite after deposition, resulting in the early cementation of such limestones. In chalk, absence of this calcium carbonate conversion process prevented early cementation, which partially accounts for chalk's high porosity. Chalk
1612-494: The dolomitized chalk has been dedolomitized back to calcite. Chalk is highly porous, with typical values of porosity ranging from 35 to 47 per cent. While it is similar in appearance to both gypsum and diatomite , chalk is identifiable by its hardness, fossil content, and its reaction to acid (it produces effervescence on contact). In Western Europe, chalk was formed in the Late Cretaceous Epoch and
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1664-437: The early Palaeocene Epoch (between 100 and 61 million years ago). It was deposited on extensive continental shelves at depths between 100 and 600 metres (330 and 1,970 ft), during a time of nonseasonal (likely arid) climate that reduced the amount of erosion from nearby exposed rock. The lack of nearby erosion explains the high purity of chalk. The coccolithophores, foraminifera, and other microscopic organisms from which
1716-472: The fallen Slaughter Stone (so named from its reddish coloration) in the early nineteenth century. It was found that the pits were an average of 0.76m deep and 1.06m in diameter. 25 of the pits contained later cremation burials inserted into their upper fills along with long bone pins which may have secured leather or cloth bags used to hold the remains. Their presence makes Stonehenge Britain's oldest cremation cemetery. The pits appear to have been refilled with
1768-401: The freshly excavated chalk rubble soon after being dug as no weathering has been noted on the chalk sides of the pits. They may also have been dug out and refilled numerous times. The holes are in an accurate, 271.6m circumference circle, distributed around the edge of the area enclosed by Stonehenge's earth bank, with a standard deviation in their positioning of 0.4m. The circle they describe
1820-474: The ground and noted them in his records. These features were ignored or not seen by the later antiquarians to investigate the site, and it was not until the 1920s during the work carried out by Colonel William Hawley that Hawley's assistant Robert Newall identified a ring of pits he named in honour of Aubrey and his early survey. The depressions seen by Aubrey himself are more likely to have been different features from those that now bear his name. Mike Pitts in
1872-492: The holes although all these methods, including Hoyle's, require a high level of astronomical awareness and a grasp of some very abstract concepts including knowing where and when to first position the stones around the circle. It has also been pointed out by R. Colton and R. L. Martin that simpler methods exist, based on observing the position of each moonrise, which would have worked just as well and which would not require moving numerous markers amongst 56 holes. This diminishes
1924-454: The holes are largely a product of the interpretation of them as being simple pits without any structural features. This approach has required finding an explanation which tends towards the theory that the holes were repeatedly dug, filled and redug and excludes possibilities relating to any possible timber posts standing in them. The theory that they may have been used to hold temporary markers for use in astronomical observations gained credence in
1976-562: The holes are marked at the Stonehenge site by white discs laid in the ground surface. Archaeologists number them 1 to 56 counting clockwise from the later Slaughter Stone at the eastern side of the north east entrance. Hawley reburied the human cremations he found, placing them in the backfilled hole number 7. These remains were re-excavated in August 2008 as part of the Stonehenge Riverside Project . A plaque dating from
2028-696: The holes has shown that a 56-sided polygon can be generated by the simple use of square and circle geometry. Aubrey Burl also notes that the azimuth of the Heel Stone, beyond the Aubrey Circle, marks the midpoint in the swing of the Moon between major and minor standstill points, at 51.3 degrees. The true purpose of the holes may never be known, although future excavation of the remaining twenty-four using modern archaeological techniques will certainly provide more information. 51°10′45″N 1°49′32″W / 51.179133°N 1.825593°W / 51.179133; -1.825593 Chalk Chalk
2080-420: The holes predates the megalithic phases of Stonehenge. From this stratigraphic evidence it is therefore likely that the holes were dug during the first phase of the monument, Stonehenge 1 (around 3100 BC) and were then reused for burials during Stonehenge 2 in successive centuries. By the time the standing stones of Stonehenge 3 were erected (around 2600 BC), the holes had fallen out of use. The positions of
2132-450: The holes' purpose was the lunar eclipse , which occurs on average about once a year on a 346.62 day cycle. Lunar eclipses are not always visible as the Moon may be below the horizon as it moves across the sky, but over 18 to 19 years (18.61 years to be precise) the date and position of a visible eclipse will return to its beginning point on the horizon again. As the motion of the Moon's orbit also causes it to work its way across
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2184-528: The mineral gypsum ( calcium sulfate ). While gypsum-based blackboard chalk is the lowest cost to produce, and thus widely used in the developing world , use of carbonate-based chalk produces larger particles and thus less dust, and it is marketed as "dustless chalk". Coloured chalks, pastel chalks, and sidewalk chalk (shaped into larger sticks and often coloured), used to draw on sidewalks , streets, and driveways , are primarily made of gypsum rather than calcium carbonate chalk. Magnesium carbonate chalk
2236-562: The most famous is the extensive complex at Grimes Graves in Norfolk . Chalk was traditionally used in recreation. In field sports, such as tennis played on grass, powdered chalk was used to mark the boundary lines of the playing field or court. If a ball hits the line, a cloud of chalk or pigment dust will be visible. In recent years, powdered chalk has been replaced with titanium dioxide . In gymnastics, rock-climbing, weightlifting and tug of war , chalk — now usually magnesium carbonate —
2288-575: The other two stones occupy those same opposing points, an eclipse can be guaranteed. This also has the additional benefit of not needing any standing stones to be present at the site. On astronomical symbolism several analysts from Gerald Hawkins to Anthony Johnson have noted that Plutarch reported that Set in Egyptian myth or Typhon in Greek myth was identified as the shadow of the Earth which covers
2340-554: The pits. If the putative timbers were purposefully removed when they fell out of use, then even this evidence would be difficult to spot however. The lack of full documentation from the early Stonehenge digs in the twentieth century and the disturbance caused by the insertion of the later cremations during Stonehenge 2 have also added to the uncertainty over the function of the holes. In a survey of twentieth-century excavations at Stonehenge, English Heritage 's Stonehenge in its landscape , archaeologist Karen Walker collated and studied
2392-466: The point of the midsummer sunrise, viewed from the centre of the henge. But the Heelstone is now attributed to Stonehenge 3 and was therefore not contemporary with the holes. It has been suggested that the Aubrey holes were originally intended to be postholes containing timbers or stones but this is uncertain. Analogous timber circles at sites such as Woodhenge have influenced this interpretation;
2444-540: The positioning of the Aubrey Hole circle relative to the earth bank and ditch at Stonehenge is reproduced at similar sites with rings of timber postholes. That the holes appear to have been filled soon after excavation and then possibly redug does not exclude the possibility that they held timber posts which were replaced intermittently. No evidence of postpipes has been recovered with the holes although modern archaeological excavation techniques have not been applied to
2496-425: The recurrence of a lunar eclipse on the same azimuth , that which aligned with the Heel Stone, every 56 years. Going further, by placing marker stones at the ninth, eighteenth, twenty-eighth, thirty-seventh, forty-sixth and fifty sixth holes, Hawkins deduced that other intermediate lunar eclipses could also be predicted. More recent examination, notably by Richard Atkinson, has proved Hawkins largely wrong, as it
2548-569: The site at this stage to Woodhenge, The Sanctuary near Avebury and other Neolithic timber circles. Such a view contradicts the archaeo-astronomical view of the holes as being a unique predictive device. In fact, early Stonehenge may have been barely different from the other Neolithic timber circles of the British Isles, which had varying numbers of postholes and orientations and could therefore not have been used for in island-wide eclipse predicting. The interpretation of such timber circles
2600-427: The sky on an 18.61 year cycle in what is known as the journey between major and minor standstill and back, the theory that this period was both measurable and useful to Neolithic peoples seemed attractive. Lunar movements may have had calendrical significance to early peoples, especially farmers who would have benefited from the division of the year into periods which indicated the best times for planting. 18.61
2652-436: The small particles of chalk make it a substance ideal for cleaning and polishing. For example, toothpaste commonly contains small amounts of chalk, which serves as a mild abrasive . Polishing chalk is chalk prepared with a carefully controlled grain size, for very fine polishing of metals. French chalk (also known as tailor's chalk) is traditionally a hard chalk used to make temporary markings on cloth, mainly by tailors . It
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#17327719934302704-436: The surviving records from all the earlier work on the holes and concluded that "Although the evidence is inconclusive, and will no doubt be the subject of continued debate, the authors are inclined to support the view that the Aubrey Holes held posts, which were removed, rather than burnt in situ or left to decay." In August 2008, further excavation of Aubrey Hole 7 by Mike Parker Pearson , Mike Pitts and Julian Richards led
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