A black limestone cobble from West Kennet

The cobble,  found in 2009 and held in Terence's collection of samples since then.

Front of stone, also showing flattish side facet and brachiopod (?) impression towards the tip.

Back of stone

Back of stone -- note intersecting hairline fractures with calcite (?) fills.  In places these "veins" stand proud of the cobble surface.

Largest fossil trace -- side of stone

Prominent circular fossil trace on side of stone

Find location, downslope and to the north of the West Kennet long barrow.  

Many thanks to Terence Meaden and Tony Hinchliffe for sending through an erratic cobble found near the West Kennet burial mound.  It was found by Terence on September 19th, 2009, during a field walking exercise in a ploughed field, not far from a footpath called Gunsight Lane — grid ref SU 106 682.  It's a muddy natural track which is not widely used — apparently it was never metalled or asphalted.

The find is a cobble or stone, dark grey or black in colour, 700 g in weight, easy to fit in the palm of a hand.  Max length 11 cm, max width 8 cm.  Rough wedge or bullet shape.  First impression is that it is very heavy for its size.  Heavily abraded with sub-angular edges.  It reminds me of the Newall Boulder, but it is much smaller. There are four major facets and several smaller ones. Pointed bottom end, and rather rough flattish top surface. Difficult to discern any “generations" of breakage. In several places there are fossil traces, some diverging ridges, two areas of small parallel ridges, and one prominent semi-circular ridge -- so this is essentially a sedimentary rock. 

The fossil imprint: I thought first of all that it was a brachiopod, but then saw that the ridges are not very regular and divergent, and that some appear to be wavy.  And at the base there are signs of several circles that look like tube cross-sections. Maybe this is a “ghost crinoid fossil” replaced by dolomite crystals?  Crinoids are common in the Black Rock Limestone Group. Dolomites vary in colour and are most often lighter in colour — but can be dark grey or black. They are heavier and more dense than the parent limestone. Another characteristic of dolomites is the intense pattern of intersecting hairline fractures filled with calcite (?). This stone is full of them.

Another possibility is that the main fossil imprint is a Cordaites ribbed structure, widely found in the Pennant Sandstones of eastern Wales and western England.  But if this is Carboniferous Limestone then that would be ruled out.

The cobble has a slightly shiny surface patina, but there is no obvious weathering crust.   Multiple small fracture scars. Abundant whitish scratches are modern — presumably plough damage. The surface can be scratched with a penknife blade.  

Strong fizzing reaction when sprayed with limescale remover -- this confirms that this is limestone.  So does it belong to the Black Rock Limestone Group (Lower Carboniferous), possibly partly dolomitised, possibly from the Mendips?

Traces of glaciation? No obvious striations, but this cobble is clearly not derived from a scree slope or frost-shattered slope breccia. At the other end of the shape scale, it is clearly not from a beach or river aggradation either. It might have suffered transport in a glacio-fluvial environment, but its overall bullet shape and abundant fracture scars point towards transport by ice.  I don't think this erratic has anything to do with the oolitic limestone slabs used in the West Kennet burial chamber; it has no signs of recent or prehistoric "breakage" and is a discrete clast heavily abraded on all edges.

Carboniferous Limestone erratics are very rare around the Bristol Channel, and I do not know of any others on the chalklands of Salisbury Plain or the Downs. If this really is a Mendip erratic, that is rather interesting……..

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Could this find be associated with the sections of dry stone walling at West Kennet?  It is assumed that in the long barrow there were sections of dry walling with small, thin slabs of limestone imported from outside the area.   Much of the stone used as dry walling in the WKLB was identified as originating from Calne, 7 miles to the west, but some might have come from an area between Frome and Bradford on Avon, some 20 miles to the south - west.   It is claimed that well over a ton of this 'foreign' stone was imported for the building of the barrow.  Almost all of the original dry walling had rotted by the 1950s, so it was replaced by new stone from Calne, probably brought in under instructions from Stuart Piggott.

Tabular oolitic limestone was also used in dry stone walling at Adam's Grave.  Pieces of oolite (from the Frome area?) are also known from the unchambered mounds of Shepperd's Shore, Easton Down, Horslip and Kitchen Down, and from Windmill Hill ( Piggott 1962). 

My initial impression is that this "Meaden cobble" is not oolitic limestone, but that it might have come from the Frome area.  This is what AI tells me abour dark coloured limestones in north Somerset:

Dark-colored limestones in North Somerset are primarily found within two geological formations: the Carboniferous Black Rock Limestone and the Jurassic Blue Lias.

Black Rock Limestone (Carboniferous)
This is the most prominent "dark" limestone in the region, typically described as dark grey to black due to its composition and fossil content.
• Mendip Hills: The formation is extensive across the Mendip plateau, forming major features in the western Mendips.
• Burrington Combe: Very well exposed in the upper parts of this gorge.
• Cheddar Area: Significant exposures occur around Cheddar, including the Cheddar Limestone Member, which is a 38-meter thick dark limestone.
• Coastal Outcrops: Dark Carboniferous limestones are visible at Middle Hope (north of Weston-super-Mare) and Brean Down.
• Quarries: It is actively or historically quarried at locations like Holwell and Cannington Park near Bridgwater. 

Blue Lias (Lower Jurassic)
The "Blue" Lias is named for its distinctive blue-grey to dark grey appearance, which comes from its high sulphide-bearing clay content.
• Coastal Cliffs: The most famous exposures are along the North Somerset coast, particularly between Kilve, Lilstock, and Blue Anchor. These cliffs show rhythmic layers of dark shales and limestones.

Info dug up on the web:

Black Rock Limestone Subgroup

The Black Rock Limestone is the most fossiliferous part of the Carboniferous Limestone in the Mendips. The remains of crinoids, brachiopods and corals are especially abundant, and three broad faunal subdivisions can be recognised. In the lowest subdivision brachiopods are dominant, such as Cleiothyridina, Dictyoclostus, Pugilis, Rhipidomella, Rugosochonetes and Syringothyris.

This interval is similar to the fauna of the Avon Group, but can be distinguished by the presence of the coral Zaphrentites delanouei and the brachiopod Rugosochonetes vaughani. The middle part of the Black Rock Limestone is characterised by a rich coral fauna, particularly Caninophyllum, Caninia, Cyathaxonia, Cyathoclisia, Fasciculophyllum and Sychnoelasma.

In the upper part of the Black Rock Limestone the coral Siphonophyllia cylindrica is diagnostic and brachiopods, such as Pustula cf. pustuliformis, become an increasingly important part of the fauna. 

Some fragments were knocked off the cobble on its blunt end on 20th Jan 2026 for further analysis:

Note the very dark colour and calcite (?) veins

Close-up of the fresh cobble surface following removal of a flake.  Click to enlarge

Sample taken from the cobble on 20 Jan 2026.  Click to enlarge

For comparison, here is an image of calcite veins and "micro veins" in Carboniferous Limestone, Three Cliffs Bay, Gower:

Thanks to Jessica.

I will hazard a guess and suggest that the fossil imprint on the Meaden Cobble may be Rugosochonetes vaughani:

If this is correct, then it points to the Black Rock Limestone..............

Apologies for the "stream of counsciousness" nature of this post!  The "Meaden Cobble" is really something of a puzzle.  Anyway, more to come. I thank several geologist contacts for their advice, and Isobel Geddes in particular.

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This is not the first erratic occurrence to be reported from West Kennet.  Here is one post:

https://brian-mountainman.blogspot.com/2024/11/more-on-west-kennet-granidiorite-mystery.html

If you want to search further on this blog, just put "West Kennet erratic" into the search box.

It is really rather bizarre that all of the authors who promote the human transport theory insist on repeating the lie that "there are no erratics on Salisbury Plain or on the chalk downs".............