Exploring Avebury - Geology
Research material to help promote the study of Avebury's sarsen stones.
Making Sarsen Stone
Account by Steve Marshall of an attempt to make a silcrete, using sand & dissolved silica: MAKING SARSEN STONE
Avebury Sarsens AttributesExploring Avebury pages 104 to 114 'Where did the stones come from?' explores the origin of all sarsens used in Avebury's monuments, and introduces the concept of a batch of 'Primary Stones' that were in the area of the Avebury Henge naturally, before any construction began. This was based on detailed fieldwork.
In 2013 Steve Marshall & Jim Gunter examined in detail every stone of the Avebury Henge & the West Kennet Avenue, recording features such as colour, types of holes etc. Their findings may be downloaded below as Excel spreadsheets:
Most of these attributes are self-evident - thickness, overall colour, other patches of colour etc, but some require explanation:
'Peeling' is a surface feature - it looks as though a thin outer layer of the stone has began to separate and peel away in fine pieces before setting hard.
'Coral Sand' - tiny specks of pink/orange that may only be seen through a magnifying glass. They were first thought to be literally grains of coral sand but are more likely to be some type of lichen.
'Sea Ivory' is a shaggy, pale grey-green lichen. Normally found by the sea, it also grows on the sarsens of Stonehenge and Avebury.
'Silica Glaze' - smooth, shiny patches of silica are found on some stones, resembling a thick, transparent pottery glaze.
'Strings' are the fossilised traces of fine plant roots that appear like boot laces.
'Sticky areas' are rough, with sharp peaks like cake icing. The sarsen appears to have become sticky before it set hard.
Avebury Stones Described
Steve Marshall & Jim Gunter's 2013 survey of the Avebury sarsens produced this - a short description of every stone of the Henge, the Longstones and West Kennet Avenue.
The Avebury Stones Described
Survey by Steve Marshall & Jim Gunter 2013
4 0.75m thick Topside in
Rectangular. Blue-grey, sparkly, orange patches, peeling, coral sand.
Inside face flattish but uneven and rough. Evenly covered with small eddy holes, many with large pinholes inside. Large vertical crease at top.
Outside face very flat and smooth with some large holes, a few pinholes, root holes and pellets. Many circular depressions 10 to 30mm diameter.
5 0.9m thick. Blue-grey, areas of pink and orange, peeling. Topside south face (probably)
Rectangular but rounded.
Inside face quite flat, slightly concave. Long, straight cracks, a few pinholes and small, shallow plant holes. More root holes in sides.
Outside face lumpy, rounded and uneven with creases and folds. Large, protruding stone chips, some large eddy holes and a few pinholes. Iron stains, haematite, raised pinholes.
6 0.5m thick Topside in
Quite rectangular but rounded. Grey, sparkly, orange patches, peeling, polishing area.
Inside face lumpy, convex and rounded. Large, shallow eddy holes and large, protruding stone chips.
Outside face flattish and rounded. Large, protruding stone chips; no holes.
7 0.6m thick Topside out
Rounded pillar. White, areas of pink and orange, peeling, coral sand.
Inside face rough and lumpy with many protruding chips of shattered flint, some large; another visible on eastern edge. Some pinholes and shallow root holes.
Outside face has folds and creases, with a couple of shallow eddy holes. Double vertical spine? Transverse root holes.
8 0.9m thick? Topside out (probably)
Square - skewed out of line to the east. Grey, lots of pink, sea ivory, coral sand.
Inside face smooth with large corrugations. No holes.
Outside face rough, lumpy and uneven. One shallow eddy hole near base. Awen symbol etched in centre.
9 0.8m thick (over 1m thick at base) Topside out
Rounded 'D' shape - known as the 'Barber Stone'. Dark grey with areas of orange and pink.
Inside face quite flat though rippled, with creases and laminations. Some large eddy holes, one prominent near centre; some clustered pinholes near edges.
Outside face flat and smooth with many large root holes, some in cross-section.
10 0.97m thick Topside out
Rectangular, rounded and lumpy. Grey, orange, pink patches, peeling.
Inside face flattish, rounded and rough; pitted all over. Large cracks and stone chips. A few root holes, some in cross section.
Outside face has large, protruding lump at top; thick laminations, many very large. Eddy holes, transverse root holes.
12 0.6m thick
Lozenge. Pink, orange, chips of rose quartz. Sparkly, peeling. Polishing area.
Inside face lumpy, concave and uneven, with cracks and creases. One shallow eddy hole at base.
Outside face very flat and rippled. A few shallow hollows and holes.
14 1.1m thick? (Over 1m) Topside in (probably)
Roughly square. Pink
Inside face quite flat, smooth and rounded. A few shallow eddy holes and one hole, 15mm diameter.
Outside face rough, lumpy and uneven, with folds and laminations. Some large but shallow hollows and large, protruding stone chips. Small protruding root on S side.
16 0.7m thick Topside in
Square. Pink, grey, orange areas.
Inside face rough and uneven. Covered with pinholes of various sizes, some inside larger hollows.
Outside face flattish and smooth with large cracks and laminations. Stained red. A few holes, 15 to 25mm diameter. One small root hole in cross-section at base. Thick silica glaze on sides.
22 Broken fragment, size uncertain. Rough, lumpy, iron stains.
24 0.9m thick Topside in (probably)
Broken into pieces, re-assembled by Keiller using cement. Dark grey/pink, some coral sand, orange patches.
Inside face smooth but uneven, with polishing areas. Some tiny pinholes, one shallow hollow. Circular feature 55mm diameter.
Outside face uneven with large corrugations. No holes.
The remains of broken iron chisels can be seen in the west side.
30 1.0m thick Topside in
Rectangular with angled top. Pink, areas of orange, silica glaze, coral sand.
Inside face flattish, slightly convex. One large pinhole at top; fine cracks.
Outside face facetted, concave. 'Seat' at north edge, no holes.
31 0.7m thick Topside out?
Almost square but rounded. Pink, areas of orange and dark pink.
Inside face flattish but rough. Many small eddy holes - largest in centre measures 40mm across, others 30mm across but only 30mm deep.
Outside face quite flat, with semicircular feature in centre. Folds, creases. One very large root hole 120mm diameter and 200mm deep. Group of large and small pinholes, some inside other hollows. Polishing area near centre. Areas of fine gravel, areas of dark pink, some coral sand.
32 0.85m thick Topside out
Rectangular, rounded. Orange-grey, areas of pink, some coral sand.
Inside face flattish, facetted, rough, with large stone chips and possible orange staining. Root hole 50mm diameter, 100mm deep.
Outside face convex with creases, folds and large root hole 70mm diameter.
33 1.0m thick Topside in
Square, skewed 30 deg to west. White/pink/orange, dark areas of silica glaze.
Inside face facetted, uneven, with cracks. Root hole 40mm diameter; other smaller, shallow eddy holes.
Outside face rough, uneven, facetted, with cracks and folds. One large hole 70mm diameter; smaller hole at top.
34 0.6m thick Topside in
Lozenge. Grey-orange, some coral sand.
Inside face flattish but rounded and rough. Two shallow eddy holes; many pinholes of different sizes. Heart-shaped feature in centre, its shape partly defined by pinholes.
Outside face very flat and smooth with fine cracks. A few pinholes.
35 0.65m to 1.1m thick Topside unknown
Bulbous, lumpy and uneven. Orange/pink.
Inside face facetted with folds and cracks. Top probably broken off. Some holes in sides.
Outside face rough and pitted with large, protruding lump.
36 0.4m thick Topside in
Lozenge with broken off corner. Orange/pink, some coral sand, rust patches.
Inside face uneven and rounded; evenly covered with small to large pinholes (2 to 20mm diameter). Red staining - base very red.
Outside face flattish, rounded and uneven. Some large, protruding stone chips. No holes except where broken (holes made a weak point?)
38 0.6m thick? Topside in
Broken off stump - holes used to break. Also has marker pillar. Very large conical root hole visible in cross-section on top. Orange/pink.
Outside face has pinholes in broken surfaces, some in cross-section and containing possible remains. One pinhole 60mm deep.
40 0.6 to 0.88m thick Topside out
Rounded, almost lozenge. Grey-orange, orange patches, peeling, some coral sand, silica glaze.
Inside face flattish and rough. A few shallow eddy holes, orange staining.
Outside face flattish and uneven. Rounded, with creases, folds and rougher areas containing stone chips. No holes.
41 0.65m thick Topside in
Broken off stump. Orange/pink/grey.
Inside face no holes; orange staining.
Outside face facetted, no holes, red staining.
42 0.65m thick Topside out
Broken into many pieces: re-assembled by Keiller using cement. Originally rectangular? Orange-grey, some coral sand.
Inside face flat but rough. One medium-sized eddy hole and a few smaller holes. Large, protruding stone chips.
Outside face flattish and rounded, with creases and heart-shaped depression in centre. Some eddy holes, more in sides.
44 Over 1m thick. Top side out
Huge, rectangular and rounded. Grey-pink, orange patches. Some peeling.
Inside face rough, lumpy and uneven with folds. Large stone chips; several shallow eddy holes of different sizes.
Outside face flattish, with large cracks and creases. Large root holes and orange staining.
46 0.9 to 1.0m thick Top side out
'The Swindon Stone' - huge lozenge. Grey/orange/pink, sea ivory, coral sand.
Inside face dark pink, flattish with creases, folds and cracks. Pink staining at base; no holes. Some circular clustered on east side. Orange patches and large grains of rose quartz.
Outside face rough and uneven, with folds and many holes. Large, protruding stone chips; some very large eddy holes and clustered pinholes - some inside larger holes.
50 0.5m thick. Top side out
Square. Pink, peeling, Sea Ivory, coral sand.
Inside face flattish with cracks and laminations. Orange staining. A few small plant holes; some protruding small stone chips.
Outside face convex and rough with creases. Coarse stone chips at top; one medium-sized plant hole.
68 0.6 to 0.9m thick. Top side in.
Skewed. Dark blue/white, orange areas, peeling, coarse texture, coral sand.
Inside face uneven, smooth (rounded), no holes.
Outside face rough, uneven, facetted with creases. No holes, large circular laminated feature in centre
73 0.8m thick on exposed edge; rest buried
Inside face rough, fractured, facetted with cracks, creases and a natural 'seat' similar to stone 1.
Outside face concave, facetted, some red staining. 60cm diameter circular depression in centre. Some small clusters of pinholes.
201 0.5 or 0.9m thick
Square-ish. Red staining at base on both sides.
Inside face flattish with creases, protruding stone chips. A few small and medium-sized holes.
Outside face facetted with concave creases and folds. Rough and pitted centre, smoother elsewhere. No holes.
206 1.0m thick?
Inside face very lumpy, uneven with some large protruding bulges. Large circular hollows, a few medium-sized eddy holes. Some plant holes inside hollows.
Outside face very lumpy, uneven, many large eddy holes with small pinholes within. Large cracks. Some groups of pinholes.
207 0.9m thick?
Inside face uneven, facetted but rounded. Some natural hollows, no holes. Possible slight red staining.
Outside face uneven, lumpy. Some eddy holes and protruding stone chips.
Cove Stone II (largest) 1.0m thick Topside in.
Inside face evenly covered in pinholes, with small eddy holes and linear depressions (perhaps made by fallen branches?). Pink/grey, orange patches, coral sand.
Outside face rough, lumpy and uneven. Protruding flints and chips, large hollow at top. Pinholes in small groups, some small plant holes. Some medium-sized raised holes. Pinholes measure 5mm to 25mm deep. Fossilised root at base?
Cove Stone I (smallest) 0.7m thick Topside out.
Overall flat, smooth, rounded. Blue-grey, peeling.
Inside face some medium-small holes and creases.
Outside face flattish but uneven; covered with large pinholes. Two circular features measuring 27cm across, rusty pinholes.
210 1.0m thick?
Only face visible is flattish, with uneven, pitted surface. Protruding flints and orange staining; some pinholes at edges.
77 Thickness unknown Topside unknown
Broadly rectangular stump barely above ground.
Pink-grey, laminated, slight reticulation, pitted, areas of dark pink.
78 1.0m thick Topside unknown
Pink-grey, sparkly, areas of orange.
Visible face is facetted and quite smooth, though pitted. Some fine cracks; no holes.
98 0.7 to 1.4m thick Topside in (probably)
Huge, rectangular, tilted slightly sideways. Pink-grey, peeling; large patches of dark pink and orange.
Inside face flattish and concave in centre. Evenly covered with creases and cracks. Many small holes and groups of large pinholes.
Outside face uneven, facetted and laminated. One large pinhole and a few smaller ones.
1 1.0m thick? Topside out (probably)
'The Devil's Chair' - huge, square but tilted slightly sideways.
Pink-grey, areas of silica glaze.
Inside face flattish with thick laminations. Large area of pinholes around eastern edge; some root holes near base and top. Some very large pinholes near centre.
Outside face rough and uneven with large, wide cracks and natural 'seat' with vertical shaft above, open to sky. Many rough holes of various sizes; a few pinholes.
101 0.8m thick? Topside in
Rectangular with angled top.
Pink-grey, lots of sparkly orange, peeling, patches of silica glaze.
Inside face uneven and rounded with creases and folds. Several small smooth (eddy?) holes; some larger circular depressions. A few large pinholes, several areas of dark coral.
Outside face rough and uneven with large protruding stone chips forming lines. Large piece of fractured flint in centre. Some large pinholes within larger holes; other large pinholes follow lines of natural creases. Rusted pinholes, some 'sticky' areas.
102 0.6m thick? Topside out
Blue-grey, peeling, some orange patches. Large areas of coral sand, rusty patches.
Inside face uneven with cracks, laminations and protruding stone chips. No holes.
Outside face smooth and rounded with some root holes and creases. A few isolated pinholes.
103 0.7m thick? Topside out
Pink-grey, sparkly, peeling, laminated.
Inside face uneven and facetted, some areas flat and smooth. Cracks, folds and large stone chips; a few shallow eddy holes.
Outside face lumpy and uneven with large cracks; some large eddy holes, root holes.
105 0.4m thick? Topside out
Blue-grey, peeling, some orange.
Inside face facetted with many cracks. eddy holes of several sizes, some inside other hollows.
Outside face rough, uneven and part-facetted. A few holes.
106 0.8m thick Topside in
Pink-grey, lots of orange.
Inside face uneven with creases, folds and large cracks. Several eddy holes of different sizes; large protruding, rounded lumps resembling the 'ear' in the WKLB. Stained red in places, purple at base.
Outside face rough and lumpy, covered with coarse stone chips; large, wide, vertical channel. Many ragged holes, one huge transverse root hole.
Originally set as a lozenge, though slipped when re-erected in 1912 and now appears almost square.
Southeast face is flattish but lumpy and uneven with large cracks and creases. One large pinhole.
Northeast face rough, uneven and lumpy with all-over pitting. A few clustered large pinholes and shallow burrows.
Vaguely rectangular and lumpy.
Northeast side lumpy and uneven with cracks and creases. Many medium-sized burrow holes (up to 300mm deep) and a few pinholes.
Southwest side facetted with fine cracks and a protruding lump. Clustered pinholes in centre, one over 300mm deep. Larger pinholes base, so almost in cross-section.
The Avebury Stones Described
Survey by Steve Marshall & Jim Gunter 2013
West Kennet Avenue
4b 0.6m thick. Topside out.
Square. Blue-grey, peeling, orange patches.
Inside face flattish but rough, with a 'seat'. Some circular depressions and a few small holes.
Outside face rough, lumpy and uneven with folds, cracks and creases. Root holes, some transverse.
13a 0.5m thick Topside out (probably)
Pillar with top sides broken off into a triangular point. Blue-grey, peeling.
Inside face stained orange. Rough, uneven and facetted with folds and cracks. Some medium-sized holes.
Outside face uneven with lumpy creases, folds and cracks. No holes.
Silica glaze on N & S sides.
13b 0.4m thick Topside in
Lozenge. Blue-grey, peeling, lots of pink.
Inside face stained red. Rough, with creases, folds and cracks. Large protruding stone chips and circular depressions.
Outside face flattish but rounded; stained red. Small plant holes and pinholes, iron stains that resemble rock varnish
14a 0.45 thick. Top side out.
Rectangular. Blue-grey, peeling, areas of orange.
Inside face smooth and flat with some protruding stone chips. Small holes in clusters.
Outside face stained dark red with convex bulge. Evenly covered with pinholes, some joined by creases.
15a 0.6m thick Topside in
Triangular. Blue-grey, lots of orange. Rose quartz in sand.
Inside face flattish but rough. Large ragged holes, some with more holes inside them. Pitted surface with protruding stone chips. Some red staining.
Outside face angular, facetted, with creases. Two small ragged holes. One hole in north side in cross section.
15b 0.5 to 0.6m thick Topside out
Pillar. White-pink, peeling, large areas of silica glaze.
Inside face smooth, with convex bulge. Smooth with slight pitting. A few shallow holes and smoothed pinholes.
Outside face smooth and flattish with overall concave bowing, cracks and creases. T-shaped root hole.
16b 0.3m thick. Top side out (probably)
Pillar. Blue-grey, areas of orange and brown; some areas of fine gravel.
Inside face uneven but flattish, one small hole. Chips.
Outside face flattish and rounded. Some pinholes and one large circular depression with pinholes inside
18a 0.55m thick. On roadside. Topside out (probably)
Asymmetrical pillar. Orange-grey, sparkly.
Inside face flat but rough; sparkly. Crack at bottom.
Outside face flattish with vertical cracks.
Northern side very rough with stone chips.
18b 0.4m thick Top side out
Rectangular with top angled to a point. Blue-grey, areas of orange, peeling.
Inside face flattish but rough with some eddy holes, pinholes and raised pinholes.
Outside face stained red. Rough but rounded, angular at base. Many holes and depressions, some large eddy holes. More holes on short sides.
19b 0.5m thick Topside in (probably)
Rectangular. Blue-grey, orange patches, peeling.
Inside face stained red, angular and uneven. Large stepped eddy holes with smaller holes within, some clustered. Large polishing area near base. Curiously, this is probably its natural underside - it may have been turned before polishing occurred.
Outside face uneven but rounded. Many medium-sized eddy holes, rough holes and pinholes, some raised.
21a Over 1m thick. On roadside Topside unknown
Square. Pink-grey, sparkly, orange areas, peeling.
Inside face very rough with some depressions.
Outside face very lumpy and rounded with deep folds. Many shallow, ragged holes.
North side very rough and lumpy but rounded with a deep groove extending to top; large protruding chips, no holes. South side has many depressions and folds.
24b 0.4m thick (ignoring bulge) Topside in
Rectangular. Blue-grey, peeling. Silica glaze on W side.
Inside face flattish but rough, with stone chips and many small eddy holes. Some rough larger circular depressions, each with a pinhole inside.
Outside face stained red; angular, facetted, smooth with pitting. Large bulge. No holes.
25b 0.5m thick Topside in
Pillar with top angled to a point. White-blue, pink, orange, peeling.
Inside face uneven but quite smooth. Large circular depression near centre with small eddy holes.
Outside face has two layers of parallel scratches, one horizontal and the other a few skewed anticlockwise. Two eddy holes and other small circular features.
26a 0.4 to 0.5m thick Topside in
Pillar. Blue-grey, peeling, areas of silica glaze.
Inside face rounded and sparkly. Several small eddy holes near edges.
Outside face stained red, uneven and facetted. Some protruding stone chips. Many very tiny holes; some round depressions with pinholes at centres. Raised 'ear' similar to one in the WKLB.
26b 0.35m thick Top side in
Lozenge. Blue-grey, orange areas, peeling, lots of fine black sediment.
Inside face flattish; large, circular natural feature in centre. Cracks, pits and depressions.
Outside face very rough with folds, cracks and some small holes. Deep root holes at bottom, some transverse.
29a 0.3m thick Topside in
Lozenge. Sparkly, blue-grey, peeling.
Inside quite flat but rounded. Some small eddy holes. Vertical cracks/creases at base, raised pinholes.
Outside smooth, stained red, no holes. Deep horizontal scratches.
31a 0.5m thick Topside in
Rectangular. Pink with orange patches, pieces of rose quartz. Silica glaze on sides, iron stains the colour of haematite.
Inside face stained dark red, flattish with some depressions and large, protruding stone chips. No holes.
Outside face rougher, with cracks, folds and large stone chips. No holes.
32a 0.42m thick (0.8m with bulge) Topside in
Rectangular. Pink-grey, lots of orange, peeling.
Repaired by Keiller with bronze bolts.
Inside face flattish but rough with stone chips and cracks. Red staining: also on both short sides.
Outside face quite smooth, no holes. Large bulge, polishing area.
32b 0.45m thick Topside out
Rectangular but rounded. Pink, peeling, orange patches, silica glaze on sides.
Inside face flattish, stained red. Many small, shallow ragged holes.
Outside face quite smooth and sparkly. Some eddy holes.
33a 0.7m thick Topside in
Square. Pink-grey, areas of orange, many rusty areas.
Orange staining at top suggests that this stone was mounted upside down by Keiller. It had already fallen and been re-erected in 1912 by Maud Cunnington but Keiller thought it was done wrongly: it seems Keiller may have been wrong.
Inside face very rough with many rough holes, rough eddy holes and depressions. Some areas very smooth.
Outside face flattish, with cracks and laminations. Some dark, rusty holes. Large slit-shaped hole in centre.
33b 0.3 to 0.7m thick Topside out
Square. Pink, peeling, Sea Ivory on both sides.
Not mounted in line with other stones: skewed 30 degrees to west.
Inside face rough and uneven; some protruding stone chips, two pinholes. Some areas of fine, rounded gravel and rose quartz.
Outside face rough and sparkly with cracks, folds and a few small, shallow eddy holes. Some root depressions.
34a 0.4m thick Topside in
Lozenge. Pink-grey, lots of orange, peeling.
Inside face stained red. Very rough, many rough holes and cracks. 'Sticky' appearance.
Outside face flattish but rough with holes and chips of stone.
Some ragged holes on north side - otherwise very smooth and stained red.
35a Top side may be facing N - if so, over 1m thick; up to 1.25m.
P-shaped, with bulge facing southwest into Avenue. Known as the 'Shark Stone' because of its unusual shape. Pink, peeling, orange areas
Inside face has holes, cracks, rough creases and folds. Rough stone chips.
Outside face stained red. Quite smooth but dimpled. Large, deep eddy hole with smaller holes inside it. Dark areas of rust. Large hole on north side; other depressions with holes inside.
35b 0.7m thick Topside in
Asymmetrical pillar. Pink-grey, lots of orange, peeling.
Inside face flattish though rippled, with (mostly small) holes inside eddy holes.
Outside face very flat but rough with large, deep eddy holes - one 45cm deep. One hole passes right through to the north side, which has more holes. Some holes on the south side, also red staining.
36a 0.45m thick Topside in
P-shaped. Pink, areas of orange.
Inside face very rough, many small holes, some bigger and rough. Lots of gravel chips, some protruding.
Outside face stained red. Very smooth and flat, with protruding vertical spine. Some holes; also holes on south edge. Etched circular features 3cm diameter. One hole flat with surface. Transverse root holes.
37a 0.6m thick (possibly 0.8m) Topside out (probably)
Lozenge - both sides quite flat. Pink-grey, patches of orange, pieces of rose quartz.
Inside face stained red. Almost no holes, slight dimples.
Outside face rough with large chips, eddy holes, transverse root holes.
37b 0.6m thick (or 0.5 or 0.7m) Topside in (probably)
P-shaped. Blue-grey, patches of orange, peeling. Patches of silica glaze.
Inside face very rough with cracks, creases, eddy holes. Small holes in centre.
Outside face rougher with cracks, large rough holes, large chips. Some red staining, mostly at bottom.
79b 1m thick.
Rounded pillar. Pink-grey, areas of orange, pieces of rose quartz, nuggets of rust. Inside face large chips of protruding flint, ragged holes with pinholes inside.
Outside small transverse root hole, pinholes, creases. Rusty patch on N side.
80b 0.6m thick.
Rounded pillar. Pink-grey, orange patches.
Inside face (E side) large pieces of rose quartz, no holes.
Outside face shallow, ragged holes, shallow large pinholes.
Example sizes of holes:
Small (2 to 3mm diameter) pinholes - depths 1mm, 10mm, 15mm, 28mm
Larger (8 to 10mm diameter) - depths 20mm, several 30mm, most 50mm.
Largest (30mm diameter) 85mm deep.
5mm diameter holes - depths 15mm, 18mm, 25mm, 40mm, 45mm, 55mm.
Pinholes 1 to 3mm diameter - depths 8mm, 10mm, 20mm, 25mm, 28mm; many at 5mm.
4mm diameter holes - 16 to 24mm deep. 8mm diameter holes - 16 to 24mm deep.
Pinholes within larger craters, diameter 3 to 4 mm - various depths from 13mm to 50mm. Most around 20mm.
Pinholes within craters - depths 15mm to 50mm. Most around 25mm.
Large holes, some cratered. Eddy holes around 50mm diameter - up to 300mm deep or more.
Papers Relating to Sarsen Stone
'Recent advances in silcrete research and their implications for the origin and palaeoenvironmental significance of sarsens'
J. Stewart Ullyott, David J. Nash and Paul A. Shaw RECENT ADVANCES 1998
'A SUMMARY OF THE GEOLOGY, SEISMICITY, GEOMORPHOLOGY AND HYDROGEOLOGY OFTHE OKAVANGO DELTA'
D.G. HUTCHINS,, L.G. HUTTON, C.R. JONES and E. P. LOENHERT. BOTSWANA 1976
'Sandstone cementation and its geomorphic and hydraulic implications' Jiøí Adamovic ADAMOVIC
'Cypress Knees: An Enduring Enigma' Christopher H. Briand CYPRESS KNEES
'Rapid formation of Rock Varnish and other rock coatings on slag deposits near Fontana, California'
R. Dorn & N.Meek DORN MEEK RAPID
Sarsen stones in Kent, by Paul Ashbee GT TOTTINGTON'The history of the major rivers of southern Britain during the Tertiary' P. L. Gibbard & J. Lewin TERTIARY RIVERS
'Provenancing of silcrete raw materials indicates long-distance transport to Tsodilo Hills, Botswana, during the Middle Stone Age'
David J. Nash, Sheila Coulson, Sigrid Staurset, J. Stewart Ullyott, Mosarwa Babutsi, Laurence Hopkinson, Martin P. Smith
'Drainage-line silcretes of the Middle Kalahari: an analogue for Cenozoic sarsen trains?' David J. Nash, Paul A. Shaw and J. Stewart Ullyott
'Micromorphology and geochemistry of groundwater silcretes in the eastern South Downs, UK'
J Stewart Ullyott and DJ Nash ULLYOT NASH 2006