A Geological Field Guide to Harkstead, Suffolk.

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A GEOLOGICAL FIELD GUIDE TO HARKSTEAD, SUFFOLK BILL GEORGE Background. This geological field guide has been compiled as part of an ongoing GeoEssex project to publicise and promote the geology of the Stour Estuary. Casual visitors to the remote village of Harkstead may not be aware of the incredibly rich geology of this area revealed by a walk along the beach (British Geological Survey 2010; George 2012; Dixon 2012). The whole walk is about 4 kilometres or 2½ miles (see Map below).

Objectives: To view the low cliff and extensive foreshore platform on the north bank of the tidal River Stour at Harkstead which exposes one of the best sections in Suffolk of the Wrabness Member of the Harwich Formation (Aldiss 2015: 87; King 2016: 338), previously recorded as London Clay. Continuing tidal erosion of the cliff and foreshore washes out many lower Eocene fossils including bird, reptile and fish remains (Fig. 1).

Pleistocene river terrace gravels and brickearth have yielded many large vertebrate remains, about 210,000 years old and Palaeolithic flint implements. The cliffs also show clear evidence of disturbance by Arctic conditions during the Ice Age. Access for this itinerary is by car. Vehicles may be parked at the Harkstead Community Centre [TM 188 348]. Toilets and refreshments may be available at the nearby Bakers Arms public house [TM 187347]. The beach is reached by footpath by turning left at the Bakers Arms into Walnut Tree Lane and turning right at Harksleigh Cottage.

Figure 1. Looking for fossils on Harkstead beach.

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Map showing car park, locations mentioned in text and church.

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Location 1 Copperas Reach sign [TM 185344]. The footpath passes a “Copperas Reach” sign displayed at the entrance to a recently reconstructed house (Fig. 2).

Figure 2. Copperas Reach sign on footpath Figure 3. Copperas stones on Harkstead to beach. beach.

Copperas Reach refers to the stretch of the River Stour at Harkstead and is named after a Copperas House which formerly stood on the south side at Ramsey, Essex (George 1991). Copperas stones (Fig. 3) were presumably imported to Ramsey from Harwich and Walton-on-the-Naze, Essex. The Ramsey Copperas House is shown on the first series editions of the 1-inch Ordnance Survey maps which were published in the early 19th century.

Follow the footpath south, towards the beach and then turn left (east) and walk along the beach. A shallow, braided stream [TM 185342] flows across the beach and is easily forded. Continue to walk east, passing a low rising cliff composed of hill wash and windblown sand.

Location 2 Low Cliff with beach outcrop of Harwich Stone Band [TM 186339]

Figure 4. Harkstead Cliff showing outcrop of Harwich stone band on beach (left).

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A low cliff composed of recent slope deposits containing occasional layers of pebbles and pieces of pottery rises from the beach at TM 186340. A few metres further on the lower Eocene Harwich Stone Band crops out at the base of the cliff and onto the beach and is easily seen by the abundance of squarish blocks of cement stone on the beach (Fig. 4). The stone band which is up to 30cm in thickness is a key marker horizon and may be traced continuously for virtually the whole length of the cliff. On the foreshore at TM 186339, about 20 metres from the face of the cliff, Harwich Stone Band may be seen sticking vertically upwards (Fig. 5). Presumably this is the eroded evidence of a rotational cliff slump formed when sea level was lower.

Figure 5. Displaced Harwich Stone Band showing evidence of rotational slump.

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Location 3 Low Cliff with Ash Bands [TM 187339].

The fine low cliff exposure a few metres to the east shows some six thin clearly defined altered ash bands (Fig. 6). The ash layers are mainly altered to bentonite.

Looking south across the tidal estuary the high cliff at Wrabness may be seen in the distance. The cliff at Wrabness shows a sequence of some 34 ash bands. The ash bands seen at Wrabness, Stutton and Harkstead are laterally persistent. These ash bands form part of the North Atlantic Igneous Province, one of the largest basaltic

Figure 6. Close up of Harkstead Cliff [TM 187339] showing Harwich Stone Band and overlying ash bands. Fallen bocks of Harwich Stone Band on beach.

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lava accumulations on Earth formed 62-53 million years ago, prior to and during the continental break-up between Europe and Greenland produced voluminous flood basalts, igneous intrusions and, as seen here, widespread pyroclastic deposits. Some 200 ash layers were laid down, stretching from Denmark, North West Germany, the Austrian Alps and south east England, including Suffolk.

Location 4 Low Cliff with section of cart track [TM 187338]

Figure 7. Cliff section [TM 187338] showing truncated infilled cart track. The Harwich Stone Band and ash band layers may be seen about 2 metres above base of cliff.

A few metres further south east a light saucer shaped feature may clearly be seen sectioned in the cliff (Fig. 7). This is an infilled abandoned cart track that would have formerly slopped to the beach and allowed cart access to the beach. At low tide the fragmentary remains of parallel wooden posts may be seen on the lower foreshore.

These may have been the supports of an associated jetty and facilitated the import and export of agricultural goods. This section provides evidence of considerable erosion of this section of the cliff. As late as the early 1970s much of the cliff base was obscured by vegetation.

Location 5 Low Cliff with Pleistocene Channel [TM 187338] About 50 metres further south east a Pleistocene river channel filled with a coarse lag gravel (Fig. 8) at its base, overlain with poorly sorted sand and gravel, is prominently exposed in the cliff (Fig. 9). Palaeolithic implements, and erratic pebbles have been found here in the beach gravel.

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Figure 8. Lag gravel at base of Pleistocene channel (centre of picture), resting on lower Eocene silty clay. Prominent Harwich Stone Band resting on clayey silt [TM 187338].

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Figure 9. Cliff [TM 187 338] showing Pleistocene channel resting on lower Eocene deposits. Pleistocene involutions near top of cliff.

Location 6 Cliff Section showing Pleistocene involutions [TM 188337]

Figure 10. Cliff section [TM 188 337] showing Harwich Formation with slightly contorted Harwich stone Band and ash bands, overlain with Pleistocene involutions.

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Much of the low cliff section at Harkstead shows evidence of very cold periglacial conditions. The involutions are up to three metres in height and the Lower Eocene Wrabness Member of the Harwich Formation is locally considerably distorted. The disturbance does not reach down to beach level. The involutions probably formed during the late Devensian, about 12,000 years ago, as the climate ameliorated, and permafrost was thawing.

Location 7 Foreshore Platform of Wrabness Member of the Harwich Formation [TM 188335] A very large foreshore platform is exposed at low tide (Fig. 11). Lower Eocene fossils collected here can be accurately assigned to the Wrabness Member of the Harwich Formation because only a few metres of this deposit is exposed in the cliff and on the foreshore (Fig. 12). This is in marked contrast to the 17-metre-high cliff at Wrabness, Essex to the south. Thousands of sharks’ teeth (Fig. 13), and other fossils, including turtle and bird bones have been collected from the foreshore in the last few years They appear to be concentrated in the fine beach gravel and along the foreshore where the Harwich Formation is being eroded by tidal scouring. A compressed log fragment about 95cm in length, 25cm in width and 15cm thick was seen embedded in the Harwich Formation exposed on the foreshore at TM 187 337 and orientated at about 280˚- almost aligned east west. Copperas stones are washed from the Harwich Formation and sorted by the tide.

Figure 11. View across foreshore platform showing low cliff of lower Eocene deposits capped by Pleistocene sands and gravels; beach; foreshore of eroding lower Eocene deposits.

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Some Harwich Formation Fossils collected from Harkstead Beach and Foreshore

Platycarya richardsoni catkin

Glueckmanotodus heinzelini shark tooth

Palaeohypotodus rutoti (Winkler, 1874) shark tooth

Striatolamia striata shark tooth

Amylodon eocenica fish palate

Amylodon eocenica fish palate

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Glueckmanotodus heinzelini shark tooth

Striatolamia striata shark tooth

Sylvestrilamia teretidens shark tooth

Acipenser toliapicus scute fragment

Glueckmanotodus heinzelini shark tooth

Striatolamia striata shark tooth

Sylvestrilamia teretidens shark tooth

Acipenser toliapicus fin ray fragment

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Ardiodus mariotti .

Isolated teeth.

Shark vertebra

Trionyx sp. carapace fragment

Phyllodus toliapicus fish palate

Shark vertebra

Trionyx sp. carapace fragment

Phyllodus toliapicus fish palate

Xiphiorhynchus sp. part of teleost caudal vertebra

Bird limb bone fragments

Trichurides sagittidens Fish tooth

Teleost vertebra

Bird limb bone fragments

Figure 12. Some Harwich Formation Fossils collected from Harkstead Beach and Foreshore.

Location 8 Low Cliff with Pleistocene gravels [TM 188336] As the cliff reduces in height towards the south east of the section the Harwich Stone Band and ash bands are cut out by thickening sand and gravel deposits (Fig. 14). The rather disturbed sands and gravels are being attacked by tidal erosion (Fig. 15).

Accordingly, Pleistocene flint implements and erratic pebbles, eroded from the cliff, may be found among the tidally sorted beach gravel.

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Figure 13. Sharks’ teeth collected from the beach and foreshore at Harkstead.

Figure 14. Cliff section [TM188 336] showing Pleistocene sands and gravel.

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Figure 15. Base of cliff section [TM188 336] showing Pleistocene sands and gravel being actively attacked by marine erosion.

Location 9. Beach with Palaeolithic implements and erratic rocks [TM 188337] The beach below the rapidly eroding cliff of Pleistocene sand and gravel has abundant exotic rocks (Fig. 16) and occasional flint artefacts including Acheulian hand axes (Figs.

17 & 18).

Quartz breccia, schorlcemented pebble

Quartz breccia, schorl-cemented cobble

Welded tuff pebble

Tourmalinite breccia cobble

Microgranite breccia, schorlcemented showing hydraulic fracturing

Hertfordshire Puddingstone cobble

Figure 16. Some Exotic Rocks from Harkstead Beach.

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Olivine-dolerite cobbles may have been transported in glaciers from the Midland Valley of Scotland, and hornblendite boulders from even further afield. Ignimbrite boulders may be matched with rocks found in Snowdonia and transported by the ancient River Thames before its headwaters were captured by the River Severn.

Quartz-conglomerates may come from the basal Old Red Sandstone of the Welsh Borderland. Schorl-cemented quartz-breccia is typical of rocks found in abundance near Teignmouth and must have been transported from either Devon or Cornwall.

Round conglomerate pebble containing well rounded black flints came originally from Hertfordshire. The provenance of some rocks is not known. The rocks were transported either from the north by glaciers, or from the north-west by ancient rivers, during the Pleistocene period. These exotic rocks have been reworked from the Kesgrave Formation which was deposited before the Anglian Glaciation about 450,000 yearso. Flint Micraster echinoids from the Upper Chalk, about 80 million years old, may also be found in the beach gravel.

John Wymer (1985: 236-237) has detailed the Palaeolithic artefacts from this locality.

Figure 17. Flint Acheulian flint axe about 450,000 years old as found on Harkstead beach [TM 188337]. Note abundance of exotic pebbles.

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Figure 18. Two flint Acheulian hand axes recently found on Harkstead Beach.

Figure 19. Foreshore exposure of Pleistocene brickearth. This is normally obscured by silt, sand and beach material.

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The foreshore just beyond the south eastern end of the low cliff occasionally shows small patches of stony brickearth when not obscured by very recently deposited silt, sand and gravel (Fig. 19). This Pleistocene brickearth, about 210,000 years old, can be quite rich in vertebrate remains. Several eminent palaeontologists have studied the vertebrate fossils from the Pleistocene Brickearth of Harkstead. Sutcliffe and Kowalski (1972: 72) examined the rodents, Stuart (1982: 127) the large mammals and Holman (1998: 138) the reptile. The fauna includes the extinct water vole, field vole and root vole. Larger mammals include horse; rhinoceros (Bob Markham, personal communication); red deer; bison; fox; extinct straight tusked elephant and mammoth (Fig. 20). The presence of European pond turtle indicates a slightly warmer than today. The bivalve, Corbicula fluminalis, has also been recorded. The fauna would suggest a temperate, open environment of grassland with some mixed woodland (Schreve, 2015: 196).

Figure 20. Mammoth molar from Harkstead foreshore.

Location 11 Foreshore exposure of Alluvium [TM 188335] A hundred metres beyond the end of the cliff a patch of recent organic black alluvial clay may be seen on the foreshore (Fig 21). This contains much wood and occasional bones, including part of a red deer skull with attached antlers. Salt marsh may be observed here behind a low ridge of beach gravel.

From here it is best to retrace the route back to the village.

If time allows a visit to the restored Norman church of St. Mary, Harkstead [TM 194 352] which is easily reached by following Church Lane, from the Community Centre and up Fish Pond Hill. Much brown weathered cement stone, presumably from the local beach, has been incorporated into the fabric of the church exterior (Fig. 22).

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Figure 21. Foreshore showing patches of Alluvium [TM 188335]. To the left of the gravel ridge is salt marsh, not visible in this photograph.

Figure 22. Norman church of St. Mary, Harkstead [TM 194 352]. Much local brown weathered cement stone used in the structure.

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References Aldiss, D.T. (2015). Palaeogene in Lee, J.R., Woods, M.A. & Moorcock, B.S.P. (editors).

(2015). British Regional Geology: East Anglia (Fifth edition). British Geological Survey. ISBN 978-0852-823-9. 273 pages.

British Geological Survey. (2010). Colchester and Brightlingsea. England and Wales Sheet 224 and 242 Bedrock and Superficial Deposits. 1:50 000. (Keyworth, Nottingham: British Geological Survey).

Dixon, R. (2012). The Suffolk Geocoast – The London Clay of Nacton and Harkstead shores. Suffolk Natural History: Trans. Suffolk Nat. Soc. 48: 153-156.

George, W.H. (1991). Copperas and Copperas Tokens of Essex and Kent. 22 pages.

George, W.H. (2012). Field guide to the Harwich Formation and Pleistocene deposits of Harkstead, Suffolk. In A Celebration of Suffolk geology: GeoSuffolk 10th anniversary volume 476 pages. Edited by Roger Dixon. ISBN 0-9508154-7-0. Pages 133-147.

Good, C. & Plouviez, J. (2007). The Archaeology of the Suffolk Coast. Archaeological Service Report. Suffolk County Archaeological Service. 76 pages. Available online.

Holman, J. A. (1998). Pleistocene Amphibians and Reptiles in Britain and Europe.

Oxford University Press. ISBN 0-19-511232-6. 254 pages.

King, C. (2016). A revised correlation of Tertiary rocks in the British Isles and adjacent areas of NW Europe. Geological Society special report 27. ISBN 978-1-86239-728-6.

719 pages.

Schreve, D. C. (2015). Quaternary Mammals in Lee, J.R., Woods, M.A. & Moorlock, B.S.P. (editors). (2015). British Regional Geology: East Anglia (Fifth edition). British Geological Survey. ISBN 978-0852-823-9. 273 pages.

Stuart, A.J. (1982). Pleistocene Vertebrates in the British Isles. Longman. ISBN 0-58230069-X. 212 pages.

Sutcliffe, A.J. & Kowalski, K. (1976). Pleistocene Rodents of the British Isles. Bulletin of the British Museum (Natural History) Geology Vol. 27 (2): 33-147.

Wymer, J. (1985). The Palaeolithic Sites of East Anglia. Geo Books. Cambridge. ISBN 0 86094 147 7. 440 pages.

Bill George william-george@lineone.net

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