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On the occurrence of a mollusc fauna in the Red Crag pebble bed from Mason's Pit, Great Blakenham, Suffolk
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On the occurrence of a mollusc fauna in the Red Crag pebble bed from Mason's Pit, Great Blakenham, Suffolk R. G. Dixon DIXON, R.G. 2005. On the occurrence of a mollusc fauna in the Red Crag pebble bed from Mason's Pit, Great Blakenham, Suffolk. Proceedings of the Geologists' Association, 116, 139-142. An indigenous mollusc fauna dominated by Mya arenaria has been discovered in the Red Crag pebble bed at Great Blakenham and is described here. It is the first time a fauna has been recorded from this location at this horizon. Key words: Red Crag, Pliocene, Great Blakenham, Suffolk The White House, 7 Chapel Street, Woodbridge, Suffolk IPl2 4NF, UK
Following the chance discovery by GeoSuffolk (Suffolk RIGS) members on March 30, 2004 of articulated moulds of the bivalve Mya arenaria in the supposed Pliocene Red Crag pebble bed at Mason's Pit, Great Blakenham, a return visit was made by the author and Bob Markham on August 20 to record the site formally and collect specimens for Ipswich Museum. The geology of the quarry complex at Great Blakenham [Grid Reference TM 108 502] on the west side of the Gipping Valley is well known (Fig. I). The Chalk, described by Markham (l967a), was quarried from Mason's Pit for cement and comprises the Zone of Gonioteuthis granulata extending down to the Zone of Marsupites testudinarius towards the base of the pit. This is overlain by a supposed Red Crag conglomerate (Fig. 2). This, in turn, is overlain by Creeting Sands, Kesgrave Sand and Gravel and other deposits described in detail by Allen (1984, 1988) and showing fine new exposures at the time of writing. The adjacent Rampant Fields clay pit shows the overlying Lowestoft/Gipping Till (Chalky Boulder Clay), which yields a huge variety of Mesozoic erratics. The pits have been visited by GA field excursions many times - see, for example, Boswell (1938), when over 70 members used specially hired trolley buses for conveyance from Ipswich to the nearby Bramford Road terminus; Ovey & Pitcher (1948); Baden-Powell & West (1960); and Spencer (1966). Many of the earlier visits concentrated on the Boulder Clay and erratics, but more recent interest has been in the Creeting Sands and Kesgrave Gravel proto-Thames deposits. However, these fine sections are now being lost. Masons Pit is a land-fill site and the clay pit is the site of the proposed multi-million pound SnOasis project. The Red Crag pebble bed ('Basement Bed') in Mason's Pit is a c. 30 em thick brownish-red poorly sorted sandy or muddy fine sand conglomerate of flint Proceedings of the Geologists' Association, 116, 139-142.
pebbles with abundant phosphatic nodules and cemented by iron oxide, often forming an 'ironstone' (Fig. 3). It contains occasional mineralized Cetacean and other bone fragments, sharks teeth and pieces of ray palate. The flint pebbles are mostly angular to sub-rounded and up to 150 mm in diameter. The flints and phosphatic nodules occasionally show impressions characteristic of barnacle attachment or borings. Clay and mudstone pebbles, some of which are bored, are also found. There are no obvious laminations or other bedding features. The bed rests unconformably upon the Chalk, the generally planar surface of which resembles a wave-cut platform, but which is irregular, hollowed and uneven in detail. The boundary with the overlying Creeting Sands is sharp. The sediment is evidently decalcified and, apart from some questionable moulds of Cardium fragments, neither invertebrate fossils nor pollen have ever been found before from this horizon at Great Blakenham. The recent important discovery was of abundant external and internal moulds ('steinkern') of adult Mya arenaria from a section of the pebble bed less than 20 em thick and extending for about 3 m at the western end of the pit. The full extent of the occurrence is difficult to estimate because exposure is so poor. The moulds show that both valves were together and closed upon death, and their upright or near upright orientation further indicates that the shells are in their life position. They are spaced only a few centimetres apart. Large Cardium edule moulds were also commonly present, but no articulated or obviously entire ones. Moulds show that other (unidentifiable) bivalves occur, with gastropods, Serpula-type worms and possibly encrusting bryozoans. It is clear, therefore, that this assemblage represents at least part of an autochthonous, non-derived fauna, making it unusual even for the Red Crag. 0016-7878/05 $15.00
© 2005 Geologists' Association
140
R. G. DIXON
Fig. 1. View of the west end of Mason's Pit showing Chalk to the left and Creeting Sands to the right. The working terrace just left of centre is on the top of the Chalk - this is where the Red Crag Pebble Bed is found.
Mya arenaria today typically inhabits inter-tidal or shallow water, burrowing into mud or muddy sand and gravels, often in estuarine or reduced salinity conditions. It often occurs in association with Cardium and Arenicola or in other shoreline communities. The nature of both the sediment itself and the occurrence of Mya indicate that the Red Crag pebble bed at Great Blakenham is a low beach deposit in situ, rather than simply a basal, much reworked deposit which essentially took on its final depositional aspect just before it was overlain by the Creeting Sands. A similar pebble bed occurs elsewhere in the local area at Bramford (3 km), Creeting (5 km) and Battisford (6 km), and its lithostratigraphic extension westwards as far as Stansted Mountfitchet is described in Mathers & Zalasiewicz (1988). The Crag is shelly at Sproughton (6 km). The Hascot Hill deposits at Battisford (6 km), also visited several times by the GA, have been well documented by Dixon (1978) and Markham (1967b, 1972, 1975b, 1976) and contain an unambiguous Red Crag mollusc fauna. Some details on the occurrence of shells from other Red Crag localities to the west is given by Dixon (1978). A limited number of fossil finds have been recorded from this horizon at other nearby pits. Allen (1967) reported the find in 1959 from Coe's Pit, Bramford of three specimens of Balanus sp. adhering to a rounded flint pebble. Markham (1971, 1972) recorded from
Brush's Pit (formerly Coe's Pit) fragile casts and moulds of a sinistral gastropod - 'possibly Neptunea contraria' and a few dextral specimens, and several articulated mussel shells - 'possibly Mytilus edulis' - in a sandy matrix. These are currently located in the Ipswich Museum and, although extremely fragile, recent reassessment has confirmed their identification. Markham (1975a), from the same pit, recorded occasional trace fossils, similar to tubes found in shelly Red Crag to the east. Pieces of mineralized bone, fragments of ray tooth, teeth of Odontaspis, Chrysophrys and Edaphodon have also been found and are in the Museum collection. Markham.(1975a) also recorded from Bramford Old Brickyard a tooth of the shark Carcharadon megalodon (found by P. Grainger); and from a temporary exposure while constructing the AI4 Creeting bypass, 'a shark tooth, a ray tooth, phosphatised bone, and a barnacle mould (in ironstone)' (also in Ipswich Museum). Spencer (1966) noted that 'a cast of a marine shell, similar to the genus Turritella, was once observed' and, later (1971), referred to 'white sand with rare sand casts of univalve molluscs' from the Creeting Sands at Valley Farm, Sproughton. Another museum specimen, found by R. Henry in 1969 from a sand pit on the eastern side of Dales Road, Ipswich, shows at least eight external and internal moulds of entire valves of Cardium angustatum in the same state of preservation as at Great Blakenham.
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Fig. 2. Bob Mar kham demonstrate s the Pebble Bed. The sand above the Pebble Bed is not in situ.
Fig. 3. The iron-stained Pebble Bed rests unconformably on the Chalk. Flint pebbles can be seen clearly.
Although there are small but significant lithological differences with the Batti sford and Red Crag pebble beds - mainl y in there being a higher proport ion of
mud at Great Blakenh am (Dixon, 1978) - correlation of the Great B1akenham pebble bed with the Red Crag has historically been based upon general similari ties
142
R. G. DIXON
with the basal pebble bed of that deposit, including its colour, the presence of phosphatic nodules and its general position above the Chalk (or, elsewhere, the Reading Beds and Thanet Sands) and below the Creeting Sands or Norwich Crag. The pebbles are of local origin and thus indicate a pre-Baventian age, for it is not until the Baventian that pebbles from other sources become common. The stratigraphic position of the Creeting Sands, c. 11 m thick, has long been a problem and certain aspects of their interpretation remain enigmatic, but it is critical to an understanding of the position of the pebble bed. They are clean white unfossiliferous well-sorted fine- and medium-grained micaceous sands. Well-developed small- and medium-scale ripple bedding is characteristic, with flaser bedding and channelling, showing a wide variety of palaeocurrant directions, a NW-SE tidal group, a NE-SW group parallel to the palaeo-shoreline and a random group which may be wind induced. The interpretation is of tidal estuarine conditions, maybe beach, sandflat or nearshore deposits, and the deposits may be corre-
lated broadly with the Chillesford Sands, part of the Norwich Crag Formation and Bramertonian in age (Mathers & Zalasiewicz, 1988). The College Farm Silty Clay towards the top of the sands contains a Pinus woodland vegetation, with areas of heathland and is interpreted as representing high tidal flat deposits. Otherwise, there is no palaeontological evidence for the age of the sands. Discussion of the regional context can be found in Mathers & Zalasiewicz (1988) and, on a broader level, in Green & McGregor (1999). It is hoped that further visits to this locality, before it is finally overwhelmed by landfill, will yield yet more elements of this unique fauna. ACKNOWLEDGEMENTS The author would like to thank Viridor Waste Disposal Co. UK for their help on site and access permission; Bob Markham for his collaboration in the field and for his comments on the draft manuscript; and Jan Zalasiewicz for his constructive criticism of the paper.
REFERENCES Allen, C 1967. Red Crag barnacles at Bramford. Bulletin of Markham, R.AD. 1971. Notes on the pits at Bramford and the Ipswich Geological Group, 2, II. Great Blakenham. Bulletin of the Ipswich Geological Group, Allen, P. 1984. Field Guide (Revised edition, October 1984) to 9, 15. the Gipping and Waveney Valleys, Suffolk, May 1982. Markham, R.A.D. 1972. Notes on some Suffolk Crag Quaternary Research Association, Cambridge. Localities. Transactions of the Suffolk Naturalists' Society, Allen, P. 1988. Great Blakenham. In (Gibbard, P. & 15, 520-524. Zalasiewicz, l.A.; eds) Pliocene-Middle Pleistocene of East Markham, R.A.D. 1975a. Notes on some Gipping Valley Anglia Field Guide. Quaternary Research Association, Sites. Bulletin of the Ipswich Geological Group, 14, 2-3. Cambridge, 87-99. Markham, R.A.D. 1975b. Notes on some Red Crag Baden-Powell, D.F.W. & West, R.G. 1960. Summer Field Exposures. Bulletin of the Ipswich Geological Group, 15, Meeting in East Anglia. Proceedings of the Geologists' 2-4. Markham, R.AD. 1976. Notes on Geological Group 'Digs' Association, 71, 61-80. Boswell, P.G.H. 1938. Report of Whitsun Field Meeting, at Gedgrave, Battisford and Wangford. Bulletin of the Ipswich Geological Group, 18,6-9. 1938: Ipswich District. Proceedings of the Geologists' Association, 49,410-414. Mathers, S.l. & Zalasiewicz, l.A. 1988. The Red Crag and Norwich Crag Formations of southern East Anglia. Dixon, R.G. 1978. Deposits marginal to the Red Crag Basin. Bulletin of the Geological Society of Norfolk, 30, 92-104
[with loose-leaf omission distributed with Volume 31 for 1979].
Green, CP. & McGregor, D.F.M. 1999. Pre-Anglian gravel deposits of the River Thames and its tributaries between Goring and Cromer. Proceedings of the Geologists' Association, 110, 117-132.
Markham, R.A.D. 1967a. Fossils recorded from the Gipping Valley Chalk. Bulletin of the Ipswich Geological Group, 2, 1-4.
Proceedings of the Geologists' Association, 99, 261-278.
Ovey, CD. & Pitcher, W.S. 1948. Observations on the Geology of East Suffolk. Proceedings of the Geologists' Association, 59,23-34.
Spencer, H.E.P.S. 1966. Field Meeting in the Quaternary of East Suffolk. Proceedings of the Geologists' Association, 77, 371-380.
Spencer, H.E.P.S. 1971. A Contribution to the Geological History of Suffolk, Part 5. Transactions of the Suffolk Naturalists'Society, 15, 279-363.
Markham, R.AD. 1967b. Battisford Red Crag 'Dig'. Bulletin of the Ipswich Geological Group, 3, 1-4.
Manuscript received 25 October 2004; revised typescript accepted 6 May 2005
On the occurrence of a mollusc fauna in the Red Crag pebble bed from Mason's Pit, Great Blakenham, Suffolk R. G. Dixon DIXON, R.G. 2005. On the occurrence of a mollusc fauna in the Red Crag pebble bed from Mason's Pit, Great Blakenham, Suffolk. Proceedings of the Geologists' Association, 116, 139-142. An indigenous mollusc fauna dominated by Mya arenaria has been discovered in the Red Crag pebble bed at Great Blakenham and is described here. It is the first time a fauna has been recorded from this location at this horizon. Key words: Red Crag, Pliocene, Great Blakenham, Suffolk The White House, 7 Chapel Street, Woodbridge, Suffolk IPl2 4NF, UK
Following the chance discovery by GeoSuffolk (Suffolk RIGS) members on March 30, 2004 of articulated moulds of the bivalve Mya arenaria in the supposed Pliocene Red Crag pebble bed at Mason's Pit, Great Blakenham, a return visit was made by the author and Bob Markham on August 20 to record the site formally and collect specimens for Ipswich Museum. The geology of the quarry complex at Great Blakenham [Grid Reference TM 108 502] on the west side of the Gipping Valley is well known (Fig. I). The Chalk, described by Markham (l967a), was quarried from Mason's Pit for cement and comprises the Zone of Gonioteuthis granulata extending down to the Zone of Marsupites testudinarius towards the base of the pit. This is overlain by a supposed Red Crag conglomerate (Fig. 2). This, in turn, is overlain by Creeting Sands, Kesgrave Sand and Gravel and other deposits described in detail by Allen (1984, 1988) and showing fine new exposures at the time of writing. The adjacent Rampant Fields clay pit shows the overlying Lowestoft/Gipping Till (Chalky Boulder Clay), which yields a huge variety of Mesozoic erratics. The pits have been visited by GA field excursions many times - see, for example, Boswell (1938), when over 70 members used specially hired trolley buses for conveyance from Ipswich to the nearby Bramford Road terminus; Ovey & Pitcher (1948); Baden-Powell & West (1960); and Spencer (1966). Many of the earlier visits concentrated on the Boulder Clay and erratics, but more recent interest has been in the Creeting Sands and Kesgrave Gravel proto-Thames deposits. However, these fine sections are now being lost. Masons Pit is a land-fill site and the clay pit is the site of the proposed multi-million pound SnOasis project. The Red Crag pebble bed ('Basement Bed') in Mason's Pit is a c. 30 em thick brownish-red poorly sorted sandy or muddy fine sand conglomerate of flint Proceedings of the Geologists' Association, 116, 139-142.
pebbles with abundant phosphatic nodules and cemented by iron oxide, often forming an 'ironstone' (Fig. 3). It contains occasional mineralized Cetacean and other bone fragments, sharks teeth and pieces of ray palate. The flint pebbles are mostly angular to sub-rounded and up to 150 mm in diameter. The flints and phosphatic nodules occasionally show impressions characteristic of barnacle attachment or borings. Clay and mudstone pebbles, some of which are bored, are also found. There are no obvious laminations or other bedding features. The bed rests unconformably upon the Chalk, the generally planar surface of which resembles a wave-cut platform, but which is irregular, hollowed and uneven in detail. The boundary with the overlying Creeting Sands is sharp. The sediment is evidently decalcified and, apart from some questionable moulds of Cardium fragments, neither invertebrate fossils nor pollen have ever been found before from this horizon at Great Blakenham. The recent important discovery was of abundant external and internal moulds ('steinkern') of adult Mya arenaria from a section of the pebble bed less than 20 em thick and extending for about 3 m at the western end of the pit. The full extent of the occurrence is difficult to estimate because exposure is so poor. The moulds show that both valves were together and closed upon death, and their upright or near upright orientation further indicates that the shells are in their life position. They are spaced only a few centimetres apart. Large Cardium edule moulds were also commonly present, but no articulated or obviously entire ones. Moulds show that other (unidentifiable) bivalves occur, with gastropods, Serpula-type worms and possibly encrusting bryozoans. It is clear, therefore, that this assemblage represents at least part of an autochthonous, non-derived fauna, making it unusual even for the Red Crag. 0016-7878/05 $15.00
© 2005 Geologists' Association
140
R. G. DIXON
Fig. 1. View of the west end of Mason's Pit showing Chalk to the left and Creeting Sands to the right. The working terrace just left of centre is on the top of the Chalk - this is where the Red Crag Pebble Bed is found.
Mya arenaria today typically inhabits inter-tidal or shallow water, burrowing into mud or muddy sand and gravels, often in estuarine or reduced salinity conditions. It often occurs in association with Cardium and Arenicola or in other shoreline communities. The nature of both the sediment itself and the occurrence of Mya indicate that the Red Crag pebble bed at Great Blakenham is a low beach deposit in situ, rather than simply a basal, much reworked deposit which essentially took on its final depositional aspect just before it was overlain by the Creeting Sands. A similar pebble bed occurs elsewhere in the local area at Bramford (3 km), Creeting (5 km) and Battisford (6 km), and its lithostratigraphic extension westwards as far as Stansted Mountfitchet is described in Mathers & Zalasiewicz (1988). The Crag is shelly at Sproughton (6 km). The Hascot Hill deposits at Battisford (6 km), also visited several times by the GA, have been well documented by Dixon (1978) and Markham (1967b, 1972, 1975b, 1976) and contain an unambiguous Red Crag mollusc fauna. Some details on the occurrence of shells from other Red Crag localities to the west is given by Dixon (1978). A limited number of fossil finds have been recorded from this horizon at other nearby pits. Allen (1967) reported the find in 1959 from Coe's Pit, Bramford of three specimens of Balanus sp. adhering to a rounded flint pebble. Markham (1971, 1972) recorded from
Brush's Pit (formerly Coe's Pit) fragile casts and moulds of a sinistral gastropod - 'possibly Neptunea contraria' and a few dextral specimens, and several articulated mussel shells - 'possibly Mytilus edulis' - in a sandy matrix. These are currently located in the Ipswich Museum and, although extremely fragile, recent reassessment has confirmed their identification. Markham (1975a), from the same pit, recorded occasional trace fossils, similar to tubes found in shelly Red Crag to the east. Pieces of mineralized bone, fragments of ray tooth, teeth of Odontaspis, Chrysophrys and Edaphodon have also been found and are in the Museum collection. Markham.(1975a) also recorded from Bramford Old Brickyard a tooth of the shark Carcharadon megalodon (found by P. Grainger); and from a temporary exposure while constructing the AI4 Creeting bypass, 'a shark tooth, a ray tooth, phosphatised bone, and a barnacle mould (in ironstone)' (also in Ipswich Museum). Spencer (1966) noted that 'a cast of a marine shell, similar to the genus Turritella, was once observed' and, later (1971), referred to 'white sand with rare sand casts of univalve molluscs' from the Creeting Sands at Valley Farm, Sproughton. Another museum specimen, found by R. Henry in 1969 from a sand pit on the eastern side of Dales Road, Ipswich, shows at least eight external and internal moulds of entire valves of Cardium angustatum in the same state of preservation as at Great Blakenham.
MOLL USC FA U N A . SUF F O L K
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Fig. 2. Bob Mar kham demonstrate s the Pebble Bed. The sand above the Pebble Bed is not in situ.
Fig. 3. The iron-stained Pebble Bed rests unconformably on the Chalk. Flint pebbles can be seen clearly.
Although there are small but significant lithological differences with the Batti sford and Red Crag pebble beds - mainl y in there being a higher proport ion of
mud at Great Blakenh am (Dixon, 1978) - correlation of the Great B1akenham pebble bed with the Red Crag has historically been based upon general similari ties
142
R. G. DIXON
with the basal pebble bed of that deposit, including its colour, the presence of phosphatic nodules and its general position above the Chalk (or, elsewhere, the Reading Beds and Thanet Sands) and below the Creeting Sands or Norwich Crag. The pebbles are of local origin and thus indicate a pre-Baventian age, for it is not until the Baventian that pebbles from other sources become common. The stratigraphic position of the Creeting Sands, c. 11 m thick, has long been a problem and certain aspects of their interpretation remain enigmatic, but it is critical to an understanding of the position of the pebble bed. They are clean white unfossiliferous well-sorted fine- and medium-grained micaceous sands. Well-developed small- and medium-scale ripple bedding is characteristic, with flaser bedding and channelling, showing a wide variety of palaeocurrant directions, a NW-SE tidal group, a NE-SW group parallel to the palaeo-shoreline and a random group which may be wind induced. The interpretation is of tidal estuarine conditions, maybe beach, sandflat or nearshore deposits, and the deposits may be corre-
lated broadly with the Chillesford Sands, part of the Norwich Crag Formation and Bramertonian in age (Mathers & Zalasiewicz, 1988). The College Farm Silty Clay towards the top of the sands contains a Pinus woodland vegetation, with areas of heathland and is interpreted as representing high tidal flat deposits. Otherwise, there is no palaeontological evidence for the age of the sands. Discussion of the regional context can be found in Mathers & Zalasiewicz (1988) and, on a broader level, in Green & McGregor (1999). It is hoped that further visits to this locality, before it is finally overwhelmed by landfill, will yield yet more elements of this unique fauna. ACKNOWLEDGEMENTS The author would like to thank Viridor Waste Disposal Co. UK for their help on site and access permission; Bob Markham for his collaboration in the field and for his comments on the draft manuscript; and Jan Zalasiewicz for his constructive criticism of the paper.
REFERENCES Allen, C 1967. Red Crag barnacles at Bramford. Bulletin of Markham, R.AD. 1971. Notes on the pits at Bramford and the Ipswich Geological Group, 2, II. Great Blakenham. Bulletin of the Ipswich Geological Group, Allen, P. 1984. Field Guide (Revised edition, October 1984) to 9, 15. the Gipping and Waveney Valleys, Suffolk, May 1982. Markham, R.A.D. 1972. Notes on some Suffolk Crag Quaternary Research Association, Cambridge. Localities. Transactions of the Suffolk Naturalists' Society, Allen, P. 1988. Great Blakenham. In (Gibbard, P. & 15, 520-524. Zalasiewicz, l.A.; eds) Pliocene-Middle Pleistocene of East Markham, R.A.D. 1975a. Notes on some Gipping Valley Anglia Field Guide. Quaternary Research Association, Sites. Bulletin of the Ipswich Geological Group, 14, 2-3. Cambridge, 87-99. Markham, R.A.D. 1975b. Notes on some Red Crag Baden-Powell, D.F.W. & West, R.G. 1960. Summer Field Exposures. Bulletin of the Ipswich Geological Group, 15, Meeting in East Anglia. Proceedings of the Geologists' 2-4. Markham, R.AD. 1976. Notes on Geological Group 'Digs' Association, 71, 61-80. Boswell, P.G.H. 1938. Report of Whitsun Field Meeting, at Gedgrave, Battisford and Wangford. Bulletin of the Ipswich Geological Group, 18,6-9. 1938: Ipswich District. Proceedings of the Geologists' Association, 49,410-414. Mathers, S.l. & Zalasiewicz, l.A. 1988. The Red Crag and Norwich Crag Formations of southern East Anglia. Dixon, R.G. 1978. Deposits marginal to the Red Crag Basin. Bulletin of the Geological Society of Norfolk, 30, 92-104
[with loose-leaf omission distributed with Volume 31 for 1979].
Green, CP. & McGregor, D.F.M. 1999. Pre-Anglian gravel deposits of the River Thames and its tributaries between Goring and Cromer. Proceedings of the Geologists' Association, 110, 117-132.
Markham, R.A.D. 1967a. Fossils recorded from the Gipping Valley Chalk. Bulletin of the Ipswich Geological Group, 2, 1-4.
Proceedings of the Geologists' Association, 99, 261-278.
Ovey, CD. & Pitcher, W.S. 1948. Observations on the Geology of East Suffolk. Proceedings of the Geologists' Association, 59,23-34.
Spencer, H.E.P.S. 1966. Field Meeting in the Quaternary of East Suffolk. Proceedings of the Geologists' Association, 77, 371-380.
Spencer, H.E.P.S. 1971. A Contribution to the Geological History of Suffolk, Part 5. Transactions of the Suffolk Naturalists'Society, 15, 279-363.
Markham, R.AD. 1967b. Battisford Red Crag 'Dig'. Bulletin of the Ipswich Geological Group, 3, 1-4.
Manuscript received 25 October 2004; revised typescript accepted 6 May 2005