Thursday 30 March 2023

The Altar Stone - the confirmed sample

The provenance of the Altar Stone "a grey-green micaceous sandstone which is anomalous in terms of its size, weight and lithology and which is not derived from west Wales (see Bevins et al., 2020), is currently unknown. As knocking lumps off the stones is now frowned on having a certain specimen that can be in part be destructively analysed is key to categorising and then tracing the source of the rocks.

The Altar Stone is particularly interesting as unlike the bluestones which were brought from west Wales in Neolithic time no source of such a rock is there, it comes from somewhere else.

Analysis of a labeled specimen in Salisbury Museum has confirmed that is a bit of the Altar Stone and so full analysis can be performed in confidence and hopefully we are a bit closer to finding the outcrop it was dragged from. 

Photo from the paper by Richard Bevins

"The Salisbury Museum sample 2010R.240 bears a label which, although difficult to decipher in its entirety reads ‘Portion of the underpart of the Altar Stone at Stonehenge – taken by Mr Brown of Amesbury while excavating in the summer of 1844 to ascertain if any interment there – no traces of such discovered - The search was made at the request of a Swedish gentleman who was deputed by an Antiquarian Society of (sic) Sweden to obtain the skeletonsThe relics annunciate the particulars I had from Mr Brown (?) March 191845 RHB.’ The rock has a second, smaller label, which states that the rock is (incorrectly) identified as being of Blue Lias age, reading ‘The Altar is of Blue Lias and incl….d about 18 in. in the gr…’. The smaller label is quite damaged and hence in part indecipherable. The attribution offers the potential for this sample to be the first, and perhaps only, sample in historic collections which provides a record of direct sampling of the Altar Stone and as such offers the possibility that this sample can be considered as a ‘go-to’ proxy for the Altar Stone itself."


Assessing the authenticity of a sample taken from the Altar Stone at Stonehenge in 1844 using portable XRF and automated SEM-EDS,
Richard E. Bevins, Nick J.G. Pearce, Duncan Pirrie, Rob A. Ixer, Stephen Hillier, Peter Turner, Matthew Power,

Journal of Archaeological Science: Reports, Volume 49, 2023, 103973, ISSN 2352-409X,


(A copy of the full paper can be supplied on request to the authors.)

Abstract: Megalithic Stone 80 at Stonehenge, the so-called Altar Stone, is traditionally considered to be part of the bluestone assemblage, a diverse range of lithologies exotic to the Wiltshire Landscape. However, the Altar Stone, a grey-green micaceous sandstone, is anomalous when compared with the other (predominantly igneous) bluestones, in terms of its lithology, size and weight, and certainly in terms of its provenance. Recent investigations into the character of the Altar Stone have focussed on excavated fragments now attributed to be derived from the Altar Stone, as well as non-destructive portable XRF (pXRF) analysis on the Altar Stone itself (re-analysed as part of this investigation). In this study we have investigated a sample from the collections of Salisbury Museum, 2010K 240 (also referred to as Wilts 277), which bears a label recording that it was collected from the underside of the Altar Stone in 1844. We examined the sample petrographically and also by using pXRF and automated SEM-EDS techniques. Like the excavated fragments, this sample from the Altar Stone shows a distinctive mineralogy characterised by the presence of baryte and kaolinite along with abundant calcite cement. The presence of baryte leads to relatively high Ba being recorded during pXRF analysis (0.13 wt%). Combined, these results validate the history recorded on the specimen label and, as far as we know, makes this the only specimen taken purposely from that megalith. As such sample 2010K 240 provides a ‘go-to’ proxy for future studies of the Altar Stone as well as validating those samples recently assigned to the Altar Stone. In addition, this study demonstrates the vital importance of historic collection specimens and their preservation, conservation and documentation, as well as the role pXRF can play in the analysis of sensitive cultural artefacts and monuments that cannot be analysed using invasive or destructive techniques.

Tuesday 28 March 2023

Flint Nodules

Richard Osgood and his team found an ovoid stone in their recent dig at Boles Barrow.

Photo with permission Richard Osgood

There has been some speculation as to what it might be. Rob Ixer kindly notes and supplied a photo of a fossil echinoid which is very similar, he writes:

"Photographs of the round-looking flint found recently a Boles Barrow show it has the shape and look of an echinoid, more specifically an echinocorys echinoid. These are a well-known and common fossils found in the Upper Cretaceous chalk of southern England, although not as abundant as irregularly-shaped flints associated with fossil sponges. 

They are uncommon (uncommonly recorded) finds within archaeological contexts and some have been confused with ‘marbles’, etc, especially if the rather insignificant ambulacra seen on echincorys are poorly preserved. Were the flint object to be an echinoid from the local chalk then it as not travelled far. 

The chalk also is the source of another misidentified material, namely rounded mammilated marcasite nodules. Many are brought into museums (almost as often as glass and metal working slags) and said to be meteorites, there is always a fiery tale. The correct identification leads inevitably to disbelief followed by disappointment of the finder. The find of a “natural pyrite meteorite” in a prehistoric shaman’s hut Bolkow Poland (the bedrock here is Cretaceous chalk)) being a prime example. Pyrite and marcasite haven’t been reported from meteorites the iron sulphide mineral is always troilite. 

Hence this flint requires a careful inspection by a Mesozoic specialist before further speculation. I doubt this will be the find of the century."

So a fossil echinoid is very likely, a natural flint nodule quite likely and a river pebble brought onto site as a hammer stone a possibility but it appears to lack percussion marks. Other suggestions such as a stone curlew egg can be dismissed.

Some of the flint nodules in my cabinet.

As an experiment I asked to write the rest of this post.

Flint nodules form when silica, which is a component of quartz, precipitates out of a solution and replaces the chalk. The silica comes from the skeletons of tiny sponges and siliceous planktonic micro-organisms (diatoms, radiolarians) that lived in the late Cretaceous period (60-95 million years ago).

The process begins with the silica-rich skeletons of these organisms dissolving in the seawater. This leaves a solution of silica in the water. At a shallow depth beneath the seafloor, the chemical conditions are right for the silica to form into flint, which literally replaces the chalk, creating nodules of flint of odd shapes and sizes and sometimes in continuous layers.

Flint nodules can be found in many parts of the world, including Europe, Asia, and North America. They are often used to make tools and weapons, as they are very hard and can be easily sharpened. 

Fossil echinoids These fossils are commonly known as thunderstones, fairy loaves, or shepherds' crowns. 

Fossil echinoids are not archaeological, but they can be found in archaeological sites. They are formed when a sea urchin dies and its hard shell is buried in sediment. Over time, the sediment hardens into rock, and the urchin's shell is preserved as a fossil.

Fossil echinoids can be found in many parts of the world, including Europe, Asia, and North America. They are often used to study the evolution of sea urchins and to understand the ancient environments in which they lived.

There are a few cases where fossil echinoids have been found in archaeological sites. For example, in 2016, a team of archaeologists found a fossil echinoid with an Anglo-Saxon inscription on it in London. The inscription was interpreted as a religious symbol, and the discovery suggests that early Christians may have used echinoids as religious objects.

However, fossil echinoids are not typically considered to be archaeological artifacts. They are more commonly seen as geological objects that can provide insights into the ancient world.

Thursday 23 March 2023

Were cattle used to move megaliths?

Article Source: First evidence for cattle traction in Middle Neolithic Ireland: A pivotal element for resource exploitation Pigière F, Smyth J (2023) 

PLOS ONE 18(1): e0279556. 

Construction of megalithic monuments—Enabling passage tomb architecture? 

Ireland, like several northwest European regions in the 4th and 3rd millennia BC, is characterised by its megalithic architecture, and the link between megalith construction and the use of cattle for traction deserves consideration. In the Funnel Beaker (TRB) culture of northern Europe, evidence includes wheel tracks associated with the megalithic tomb at Flintbek, engravings of cattle teams yoked to two-wheeled vehicles at the Züschen I megalithic tomb, and the four-wheeled wagons with drawbars and yokes depicted on the pottery vessel from Bronocice. In the later TRB, c. 3500 cal. BC onwards, it has been argued that land clearance for cultivation with the cattle-driven ard went hand in hand with the use of the retrieved material–mostly small and medium-sized glacial erratics—for megalith construction . In 4th millennium BC Ireland, the picture is somewhat different and certainly more fragmented. As outlined above, based on the current state of knowledge, ard cultivation, wheeled transport and cattle traction seem not to appear simultaneously, and the size ranges of stones utilised in the construction of megalithic monuments frequently exceed those in TRB tombs. 

Recent programmes of radiocarbon dating and mathematical modelling have also resulted in considerable blurring of traditional tomb typo-chronologies, with early passage tombs, court tombs and portal tombs all conceivably contemporary with one another and the Kilshane cattle. Nevertheless, the small amount of pottery from the Kilshane enclosure ditch, comprising a Middle Neolithic broad-rimmed globular bowl and a single sherd from a second globular bowl, links our traction data more closely to passage tomb horizons. The absence of evidence for cattle traction (and oxen) in the Irish Neolithic has created an understandable reluctance to speculate on the construction methods of passage tombs and megalithic monuments in general. In the light of the Kilshane data, some well-recognised aspects of passage tombs as a monument class can be re-evaluated, namely their tendency to be sited at higher elevations than earlier monuments and with a high degree of inter-visibility, argued to reflect more extensively networked Middle Neolithic communities. The earliest passage tomb activity recorded to date, at Carrowmore, Co. Sligo and Baltinglass, Co. Wicklow, at c. 3700/3600 cal. BC, is in upland landscapes, with the Baltinglass tomb at an altitude of nearly 400 metres above sea level. So-called ‘developed’ passage tombs c. 3300–3000 cal. BC, such as those found 25 km to the north of Kilshane in the Boyne Valley, have long been recognised as incorporating kerbstones, orthostats and other stone elements sourced from long distances, up to 75 km in the case of quartz and granite cobbles from Newgrange. In these scenarios, cattle may have been used and even enabled the transport of both large and small stones over long distances and to higher terrain, as well as considerably easing efforts at a more local scale. Once on site, manoeuvring large structural stones into position would presumably have been easier with animal traction.