Caution: this page is a very tentative and incomplete attempt to reconcile the terminology of this very complex group of strata, as an aid to identification of stone used for ancient artefacts. It probably contains many errors, and readers should use it with caution !
The description is based on the type-locality, Durlston Bay, Swanage. Columns 1-3 refer to the numbering, description and thickness given by Clements 1993; column 4 to Bristow 1857 as reprinted in Damon 1884; column 5 to the specimens displayed at Langton Matravers Museum.
I have used the traditional but informal division into Upper, Middle and Lower Purbeck, but my more detailed stratigraphical terminology is basically that of Clements (1993), who recognises two Formations and fifteen Members within the Group.
In column 6, "S" means I have a sample from the type-locality; "S ?ident", uncertainty whether the sample is really from the bed with this DB number; "P" means that I have a photograph, "Pf" that the photo shows a fossil; numbers after a photo reference indicate film and frame. "Rockfalls" means that my study of the type-locality was impeded by fallen material. Numbers preceded by "WB" relate to Ensom's section of the Purbeck Beds at Worbarrow Bay.
Ellipses (...), or gaps in the numbered sequence of strata, indicate that beds have been omitted from this list. if Rockfalls are not mentioned, omitted beds are mostly shales or other soft material that are probably not of interest as workable stone. The main exception is the Cypris Freestones Member and below (Lower Purbeck), which includes important workable stones that are not well displayed at the type-locality, and must be studied at locations farther west.
For the appearance of some beds of the Purbeck Limestone see the
website of WJ
Haysom and Son and Lander's Quarries.
There is also
a
stone catalogue at Archaeology Data Service
(you may need to enable cookies and javascript).
The common fossils of the Purbeck Limestone group are gastropods, bivalves and ostracods; follow this link for details.
Upper Purbeck. Photograph, general view
DB | Clements' description | metres | Bristow-Damon | Langton Mus. | Notes |
---|---|---|---|---|---|
Upper Cypris Clays and Shales Member | |||||
... | ... | ||||
244b | Upper PM = Blue Marble; Viviparus limestone | 0.76 | 91 | S, Photo, 2002-04:5.18 | |
... | ... | ||||
241 | Lower PM = Red Marble; Viviparus limestone | 0.81 | 89 | 1a, Red PM | S, Photo, 2002-04:5.13 |
240 | |||||
239 | Unio Bed | 0.30 | 87 | S | |
238 | |||||
237 | Green Marble; Massive Viviparus biosparite | 0.30 | 85 | 1b, Green PM | S, Photo, 2002-04:5.12 |
... | (shales etc.) | ... | 84 | ||
225 | biosparite | 0.15 | S, P 2002-04:5.11 | ||
224 | shales with thin limestones | 0.53 | |||
Unio Member | |||||
223 | Greenish biosparite | 0.15 | 83 | S, Pf. My photo 2002-04:5.14 shows a fossil found in the upper surface of this bed which is so far unidentified. Suggestions welcome. | |
222 | |||||
221 | complex, incl. Crocodile Bed, bottom limestone cemented to bed below | 0.38-0.53 | 81-79 | S, P 2002-04:5.10 upper surface of bed. | |
Broken Shell Limestone Member | |||||
220 | Broken Shell Limestone; Massive shell-fragment biosparite | 2.90 | 78, Soft Burr | 2, Burr | S, `Soft Burr' appears to be a wrong name, the result of confusion with the basal Purbeck limestone which is so named, or else with the Dirt Bed `burrs'; see Damon 1884 p.115, Strahan 1898 p.115 on the Purbeck beds in Portland. P 2002-04:5.9 |
DB | Clements' description | metres | Bristow-Damon | Langton Mus. | Notes |
---|---|---|---|---|---|
Chief Beef Member | |||||
219 | Shales with beef | 0.46 | 77 | S, P 2002-04:5.8,22 | |
218 | Lt grey biosparite | 0.23 | 76b | S, P 2002-04:5.20,22 | |
... | ... | Rockfalls | |||
Corbula Member (part-marine) | |||||
189-8 | Bivalve biosparites | 0.16 | 70 | Not seen | |
... | ... | Rockfalls | |||
184-3 | Pinkish biospar/micrite, Toad's Eye (183) | 0.36 | 68 | ?Not seen | |
... | ... | Rockfalls | |||
178 | Pinkish cream shell biosparite | 0.67 | S ?ident., sandy thin-bed limest, surface crystals | ||
... | ... | Rockfalls | |||
154 | Rough-bedded bivalve biosparites and shales | 0.66 | 59 | S ?ident., 2 chips | |
Scallop Member (part-marine) | |||||
153-44 | 58, White Roach | 3, Rag? | Rockfalls | ||
Intermarine Member (Upper Building Stones) | |||||
145 | shale | 0.10 | |||
144-141 | Laning Vein | 2.20 | 56-57 | 4, Lannen Vein | 3 S, P 2002-04:5.25 |
140e-b | shales and limestones | c.0.60 | |||
140a | Royal Limestone | 0.30 | 55 | 5, Royal | S ?ident., cream shelly biosparite with green seam |
... | ... | 6, Freestone? | Rockfalls | ||
For a picture of a cliff section of the lower Intermarine and Cinder Members in Durlston Bay, follow this link | |||||
133 | Red Rag | 0.74-0.79 | 54, Red Rag | 7, Rag Mead? | S, 2 chips, coarse bivalve biosparite |
132 | calcareous mudstone | 0.30-0.25 | 53, Green shaly Marl | ||
131 | Under Rag | 0.69-0.76 | 52, Under Rag | S, coarse bivalve biosparite | |
130 | mudstone | 0.48-0.43 | 51, shales 1'9'' | ||
Freestone Vein 16': | |||||
129 | calcareous mudstones | 1.63 | ?50h-i, Shingle | Rockfalls | |
128 | mudstone/micrite | 0.23 | ?50g, Underpicking | Rockfalls | |
127-6 | sandy, muddy, calcarenite biosparites | 0.33 | ?50f Lower Shingle, rubbly limestone | Rockfalls | |
125 | massive biosparite | 0.79 | ?50e, Crab | ?8, Grub | Rockfalls. Ensom 1994 citing El-Shahat and West 1983 identifies DB125-121 with the inland `Freestone Vein' |
124c | `shaly' biospar/micrite | 0.09 | Rockfalls | ||
124b | calcareous shale | 0.05 | Rockfalls | ||
124a | rough bedded limestones; incl. bivalve biosparites | 0.30 | ?50d, Roach, hard shell-limestone | ?9, Roach | Rockfalls. Delair 1980 identifies `Pink Bed' of the Roach as Damon's bed 50d |
123 | massive biosparite with scattered sand-grains | 0.23 | ?50c, Sugar bed | ?10, Thornback | Sugar = Thornback acc. to Delair and Lander 1972; S, 2 chips, shell and shiny grains |
122 | Rubbly sandy biomicrite | 0.18 | ?11, Whetson | S, 2 chips, shelly | |
121 | Massive bivalve biosparite, weathers to `micrite' | 0.48 | ?50b, Freestone, compact sandy grey limestone | ?12, Freestone | S, crumbly, several bits, rough shelly texture; identified tentatively as the Freestone by El-Shahat and West 1983 |
120 | Cream, thinly bedded calcarenites | 0.41 | S, chip, ?sand-grains | ||
119 | Dark grey ostracod shales grading into biosparites | 0.43 | S, chip, ?shelly | ||
118 | Massive looking hard limestone, thin laminae, ostracod seams weather proud | 0.30 | ?50a, Blue bed | S, 3 small pieces | |
5.45 total = c.18' | Bottom of Freestone Vein | ||||
117 | calcareous clays | 0.11 | |||
116b | Cream (bio)micrites | 0.56 | ?49, Lias, 2'11" | WB123 = DB115-117, Ensom 2002b p.223 | |
116a | Thin-bedded biospar/micrites | 0.20-0.15 | ?48, Lias Rag, 2'4" | S, hand-size and smaller chip | |
115 | Shales and clays | 0.43 | 47 Dark sandy Marl 1'4" | ||
114 | Interbedded thin limestones and shales | 0.94 | 46, Laper 3'0" | 13, Laper | Downs Vein = Laper = Bristow 46 acc. to Delair and Lander 1972; S, cf. roofing-stone |
(14, Grey Bed) | |||||
113 | Massive limestone with chert near top, crowded with small lamellibranchs | 0.56 | 45d, Shell-limestone 2'9" | 15, Downs Vein | Not Tombstone bed (Arkell 1944); Downs Vein (Salisbury 2002, Ensom 2002b p.223); S, shelly |
112 | Shales and limestones | 0.23 | 45c-a, marl, limestone, shale 9" | 15, Downs Vein? | |
Picture of cliff section of the lower Intermarine and Cinder Members in Durlston Bay, May 2002: large (300K) small (77K) © John Palmer, 2002-04:5.23 (east) and 2002-05:6.5 (west) | |||||
Cinder Member | |||||
111 | Massive Praeexogyra distorta shell bank | 2.95 | 44-43 | 16, Cinder | S, P 2002-04:5.23, 2002-05:6.4, 5 |
DB | Clements' description | metres | Bristow-Damon | Langton Mus. | Notes |
---|---|---|---|---|---|
Cherty Freshwater Member (Lower Building Stones) | |||||
110 | Dk grey shales | 0.41 | WB118 approx. (Ensom 2002b p.223) | ||
109 | Shales | 0.038 | |||
108 | Feather Bed, cream bivalve biosparite, Thalassinoides on base of bedding planes | 0.61 | 42, Feather or Button | 17, Button | Feather Bed, Salisbury 2002; S, taken from a bed adjacent to Thalassinoides |
107 | micrites grading softer downwards | 0.14 | |||
106 | Thin bedded biosparites | 0.08 | |||
105 | Calcareous mudstone | 0.24 | |||
104 | Calcareous clays | 0.19 | |||
103 | Massive limestone with chert near base, footprints on underside | 0.25 | 36, Cap | 18, Cap | Cap = DB103 acc. to Ensom 1986 and Ensom 2002b p.223. DB103 = WB117 acc. to Ensom 1994 (p.80 and fig.2). See note at end. |
102 | Shales with thin sandy biosparites at base | c.0.46 | 35, Sly | 19, Sly | Sunnydown Sly bed, and approx. WB116: Ensom 1987 fig.1, Ensom 1988 corrected by Ensom 1989, Ensom 2002b p.223, Salisbury 2002 |
101 | Cream weathering biospar/micrites, bivalves, gastropods | 1.40 | 34 | Here or below: 20, Five bed (or Six bed); 21, White; 22, Brassy; 23, Tompson (Tombstone) | New Vein acc. to Ensom 1987 fig.1, and to Salisbury 2002; S with shell-fragments |
100 | Gypsiferous shale | 0.057 | |||
99 | Muddy biosparite/micrite | 0.057 | |||
98 | Dark shale | 0.09-0.20 | |||
97 | Flint Bed; very hard biomicrites with ... chert nodules, silicified fossils | 0.84 | 31 | S, weathered, with chert; P 2002-05:6.3, 4 have this bed at beach level | |
96 | Firm shales | ||||
95 | V. hard, brittle micrite | ||||
... | ... | ||||
92 | dark grey/green shale with celestine | 0.25 | top 10" of 27 | Correlation after Clements 1966; Fern Bed, Salisbury 2002; P 2002-05:6.2 shows this bed at bottom of cliff, LBS above | |
... | ... | ||||
89 | Firm/hard clays/micrites | ||||
88 | Soft calcareous shales | ||||
87 | Hard biosparite, micrite intraclasts | 25 | |||
Marly Freshwater Member | |||||
86 | clay/micrite | 24 | P 2002-05:6.1 shows this bed at bottom of cliff and up to DB111 | ||
85 | clay/micrite | ||||
84 | argillaceous micrite | ||||
83 | Mammal Bed; a Dirt Bed; Carbonaceous, calcareous shale and clay | 21 | |||
82 | Micrite, biosparite below | ||||
81 | Micrite/clay | ||||
... | ... | ||||
75 | Dark brown shale grading down to clay | 20 |
Note to DB103: DB103 = WB117, so DB104-110 correlate only with the shaly WB118, as WB119 is the base of the Cinder Member. Where Ensom (1986, 1988) says DB103 = WB112 he is making a mistake, as explained in Ensom 1989. Ensom 2002b p.223 says DB102-110 = WB116-118.
DB | Clements' description | metres | Bristow-Damon | Langton Mus. | Notes |
---|---|---|---|---|---|
Soft Cockle Member | |||||
74 | Hard to v. firm fossiliferous micrite | 19 | |||
... | ... | ||||
43 | Clay with selenite and gypsum masses | 13 | |||
Hard Cockle Member (Clements puts `?') | |||||
42 | Laminated clay | ||||
... | ... | ||||
34 | Rough hard limestone | ||||
Cypris Freestones Member (Clements puts `?') | |||||
33 | Calcareous clay | ||||
... | (Micrites, calcareous clays, shales, sandstones) | ... | These beds correlate with the building stones of Upwey, for instance | ||
17 | (Micrites and biosparites with argillaceous partings) | ||||
16 | (Between clay and micrite) | ||||
... | ... | ||||
11 | Thin-bedded biomicrites and fossiliferous pelsparites | ||||
10 | Broken ostracod biomicrites and micrites | Lowest bed visible at Durlston Bay (Clements) |
Described from an exposure at Kingbarrow Quarry, Portland by Strahan 1898 p.115. The numbering of beds is Strahan's; his measurements have been converted from feet and inches. Most of these strata can be seen at the adjacent site of Tout Quarry, which is shown in this photograph.
No. | Strahan's description | metres | Notes | ||
---|---|---|---|---|---|
Broken Beds Member (also seen e.g. at Durdle Door) | |||||
(none) | Platy or laminated limestone, broken and weathered ('shifting rubble') | 1.8 | ? = Broken Beds | ||
13 | Massive laminated limestone ('hard slate') | 1.2 | Also called 'Slatt', Arkell 1944 p.163 | ||
12 | Hard-streaked stone ('bacon-tier') | 0.6 | |||
(none) | Greenish clay, about | 0.05 | |||
11 | Fine-grained argillaceous limestone, drying very white; used for holystone ('Aish-tier') | 0.6 | |||
Caps and Dirt Beds Member | |||||
10 | Tufaceous limestone, used for building in the Island, chiefly in chimneys ('burr') | 0.4 | Wimbledon 1987 p.132 identifies this stratum as the top of the Cap and Dirt Beds. It is also called 'Soft Burr' (Arkell 1944 p.163) and is not to be confused with the Broken Shell Limestone of the Upper Purbeck, which is also called 'Burr'. | ||
9 | Dark carbonaceous clay with fragments of limestone and wood ('top dirt-bed') | 0 to 0.3 | |||
8 | Tufaceous limestone ('gristle'); in the lower part traversed by holes ('chaff-holes') 50--200mm diameter and 1.5--1.8m long, sometimes branching and filled with fossil-wood ... ('top-cap') | 0.6 | Also called 'Top Cap', Arkell 1944 p.163 | ||
(none) | Carbonaceous clay and gravel ('lower dirt bed') | 0.08 to 0.15 | |||
7 | Hard brown tufaceous limestone ... ('skull-cap') | 0.3 to 0.6 | |||
(none) | Carbonaceous parting; sometimes a chert-band with Ostracoda ('dirt') | 0 to 0.05 | |||
Below here is the Portland Stone Formation. |
There are many other descriptions or sections of the Purbeck beds,
including
Fisher O 1856;
Hutchins ed.3 p.685;
Mason NJ 1984