Bobbitt's Hole, Belstead

TRANSACTIONS. BOBBITT'S HOLE, INTERIM

BELSTEAD

REPORT

BY H . E . P . SPENCER, F . G . S .

TOWARDS the end of 1952 the Ipswich Corporation commenced excavations for a new sewage works at Bobbitt's Hole, in the valley of Belstead Brook, about three-quarters of a mile westward of Bourne Bridge. The work exposed glacial morainic material overlying and cutting into clay and peaty beds laid down in a lake which existed there about 150,000 years ago. Subsequently, the Upper Chalky Boulder Clay was revealed below the lake deposits, proving them to be of the inter-glacial period between the last two advances of polar ice over North West Europe. With modern mechanical methods of excavation much evidence is obscured or destroyed and it is particularly unfortunate in the present instance that no bones of the larger mammalia have been discovered in situ. With two exceptions, only fragmentary remains have been recovered ; these we owe largelv to the interest of the workmen. The excavation of a large network of more or less deep sewer trenches on the high ground between London Road and Stone Lodge Lane has exposed many sections contributing to the Solution of local glacial problems generally, and to those arising from the newly discovered inter-glacial deposits in particular.

In five separate excavations the following strata have been revealed from below upward :—Chalky Boulder Clay, grey to buff clay, detrital peaty mud ; yellow and grey mottled calcareous clay ; fluviatile sands and gravels contorted by ice pressure with rafts of displaced underlying clay, unstratified clayey gravel and above all, on an uneven surface, a very fine Loess-like sand.

The chalky boulder clay Covers much of the high ground around Ipswich except on the east. At Rushmere Hall and the White House Estates it is twelve to fifteen feet thick resting on gravel.

It has been seen in the valley at Norwich and Bramford Roads and in Stoke. This extensive deposit is believed to be the ground moraine of the third glaciation, the Saale of N.W. Europe and the Riss of the Alpine region. In the bottom of Belstead Brook Valley it rests on Chalk.

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BELSTEAD

T h e grey silty clay below the peaty bed contains no fossils of any kind and may therefore be considered to have been deposited soon after the recession of the ice before the land surface became colonised by Vegetation.

By far the most interesting Stratum is the detrital mud which is exceptionally rieh in the shells of land and freshwater mollusca, some species growing to a much greater size than at the present day. T h e r e are quantities of fruits and seeds; a large proportion are those of water plants such as Hornwort, (Ceratophyllum s p . ) ; there is also much drift-wood flattened by pressure. Some bones and teeth of fishes, frog or toad, and small mammals have been collected, the latter have been provisionally identified by Lord Cranbrook as Sorex sp., Evotomys sp., Microtus sp., Arvicola sp., Apodemus sp., and an indeterminate tibia of a bird. T h e most interesting discovery was a few bones of the European Freshwater Tortoise (Emys orbicularis L ) (this was found also by Miss Layard in the Stoke T u n n e l Beds, 1912 and 1919.*) T h e mottled calcareous clay is fĂźll of race (calcareous concretions) which is undoubtedly derived from an abundant growth of chara, since the fossil fruits of this alga are very common in the deposits ; shells are also abundant. It is possible that some of the bones of the larger mammals come f r o m this bed. This Stratum passes down into an eight inch thick purplish band resting on the peaty bed which is seven feet in thickness.

F r o m the fluviatile sands and gravels a few broken fragments of bone have been recovered. T h e bones include crushed fragments of molar and tusk of mammoth, a horn core, two metacarpals, parts of a humerus and fragments of radius of bison.

Observations in a large number of sections made during the last ten years show that the unstratified gravel must be a glacial tili and, as it is always found over all other local rocks, there can b e ' n o other explanation than that it is the produet of the last advance of polar ice. In some sections it has been found to contain boulder-like masses of local material, such as London or Reading Clay, the latter a conspicuous and easily recognised rock, Red Crag and patches or rafts of chalky boulder clay.

Alon'g the margins this gravelly tili usually passes into a cannonshot gravel with angular boulders of local hard rocks, Sarsen and London Clay Cement Stone. T h e occurrence of this coarse material suggests a lateral moraine; such a deposit has been observed in an abandoned pit near Bobbitt's Hole. In the vicinity of the site there appears to be no London Clay, the rock which normally rests on the Reading beds. Higher up the valley at Gusford Hall, in trenches some fifteen feet deep, shelly Red Crag *Proc Suffolk Inst, of Archaeology, Vol. X I V , p. 59. Proc. Prehistoric Soc. of E . Anglia, Vol. III, p. 210-9.

BOBBITT'S HOLE, BELSTEAD

55

was found resting on the Reading Clay with much weathered pieces of London Clay Cement-stone forming sparse basement bed. The bedding of the Crag is normal throughout, but the Upper part is unfossiliferous, with alternating bands of light and brown sand dipping steeply from N.W. to S.E. The Loess-like material at the top of the section is the result of wind blown dust settling in hollows, having been removed from a bare landscape during a cold dry period following the recession of the last ice sheet. At the present tims the wind blowing across bare fields in dry weather gives an observer an idea of the conditions under which this deposit was laid down.

Ever since the Ipswich Dock Commission first had the deep Channel for shipping dredged in the Orwell, bones and teeth of such animals as the mammoth, woolly rhinoceros, urus, bison, red deer and wild horse have been found whenever dredging has been carried out. These remains come from peat beds, etc., under the river which must have been laid down at the same period and under somewhat the same conditions as at Bobbitt's Hole where the few bones identifiable indicate the presence of the same type of animals. The Stoke Tunnel Beds, discovered about a Century ago when the tunnel was constructed, have yielded a similar fauna with the addition of lion, bear, wolf, fox and fresh-water tortoise. The existence of mammoth with such a rare creature as Emys may be taken as proof of the contemporary character of the deposits. In the nevvly-exposed beds, we have therefore evidence of the age of the Orwell Forest Bed and the Stoke elephant bed, which, when the examination of the pollen grains is complete, sh3ild pjt b^yo.ii all dajbt the glacial succession in East Anglia.

Two samples of the grey to buff clay from the bottom of the lake have been examined by Dr. I. W. Cornwall who reports them to be typical calcareous unweathered LOESS. The first sample was buff coloured from near the margin of the lake where the lacustrine deposits are thinnest, it consists of 8% sand, size of grain 0.06 mm.; silt 81%, 0.06 - 0.002 mm.; clay 11%, 0.002 mm. Sample number two was from a bore hole six feet below the peaty detrital mud and consisted of materials of the same grain size as thefirstbut in the proportions 10%, 75% and 15%. These results are only approximate but they indicate for thefirsttime a deposit of loess which is strictly comparable with the very extensive deposits of wind-borne material on the continent. Geologists have long doubted the existence of such rock in Britain and it is gratifying that it should be found in Suffolk where there are already other uniquely interesting strata. The grey colour of the second sample is due to the reduction of the yellowish ferric iron Compounds by organic acids from the overlying bed which has converted them into ferrous Compounds. The presence of the loess in this series of

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BOBBITT'S HOLE,

BELSTEAD

deposits is therefore of the highest importance in British Pleistocene geology and the site was already important by reason of the completeness of the strata from the intense cold of the third glaciation to the cold of the last advance of the ice.

The sequence of events revealed by the strata at Bobbitt's Hole are, first a period of intense cold represented by the chalky boulder clay below the lake deposits ; next there was a long period during which the Vegetation was absent or too scanty to prevent wind blowing away the finer soil, a cold dry phase following the retreat of the ice. Much of this dust settled in a hollow, probably already waterfilled, to a thickness of sixteen feet over the very irregulär surface of the boulder clay. As seen in the section freshwater mollusca became common before there is much visible evidence of plant life other than chara, but naturally the molluscs must have had something to feed on ; most of the shells in this zone are crushed and complete specimens cannot be collected. The lower part of the detrital bed is ash grey but it soon darkens by reason of the increasing quantity of plant remains, chiefly pieces of twig and driftwood which became waterlogged and sank, most of them are flattened bv pressure, presumably by the ice of the last glaciation. Some sixty species of shells have been provisionally identified from the beds so far ; however, as there is much material yet to be washed the final list may well be larger. The beds are by far the richest in fossils yet found in Suffolk and in addition to those already referred to there are many fragments of beetles, some of which it is hoped may be identifiable. Some change took place, for the detrital bed is replaced by a grey and yellow calcareous clay also rieh in molluscan remains, some of which are new species.

Thiere are still some small vertebrate remains and the bones of large mammals, such as bison, occur.

Above the mottled clay there are fluviatile sands and gravel from which broken bones of large mammals have been recovered, these include mammoth. It seems that at this stage the lake had become a river probably owing to increasing rainfall as the climate deteriorated owing to the impending final advance of polar ice. The sands and gravel, together with the upper part of the lake beds, are much contorted by ice pressure, while in the centre of the Valley the whole of the deposit has been replaced by unstratified gravel deposited by ice. Resting on the irregulär surface of the gravel, which is actuallv the tili of the last glaciation, is another wind-borne deposit not quite as fine as the loess, but representing another dry cold period.

Bobbitt's Hole has yielded evidence of the age of the Upper Chalky Boulder Clay which is irrefutable and observations made in other exposures in the district have shown it to be the produet of a separate glaciation and not, as has been thought, a different produet of the ice which deposited the Chalky Jurassic Boulder

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57

Clay. At Blakenham in the large clay pit, near the top of a section over twenty feet high is a brownish streaky zone representing the passage of a new ice sheet over the older boulder clay below.

An identical bed has been seen in a sewer trench between L o n d o n Road and Stone Lodge on the u p p e r part of the new Chantry Estate where there is a m u c h larger outlier of u p p e r chalky boulder clay than is shown on the geological map. T h e basal bed of this tili m a y be recognised by the vvay in which pebbles and boulders of chalk have been drawn out to f o r m lines in the direction of the m o v e m e n t of the ice owing to the resistance of the underlying rock, it is usually brownish and of a banded character ; the rock below may, or may not be contorted. Below the streaky zone t h e r e is sometimes waterlaid sand and, or, gravel deposited by meltwater running u n d e r the ice.

T h e r e are few records of E m y s orbicularis in this country, and the age of the deposits in which they were discovered has not been satisfactorily established, but it is probable some of t h e m m a y be post-glacial as are the many finds in Denmark where they occur in peat bogs. T h e i r presence indicates a climate as w a r m as the south of France where these animals still live.

It is customary during the mating season for the male tortoise to attach himself to the back of the female and force her to retract her head, quite often for so long a time as to cause her death by drowning. It follows, therefore, that in excavations m a d e by h a n d entire fossil skeletons may be discovered, especially w h e n peat is dug, as in Denmark. T h e few fragmentary remains recently discovered, by reason of the newness of the fractures suggests that at least a fairly complete specimen was smashed u p by the mechanical excavator.

Until recent observations showed some local deposits to be the p r o d u c t of the last glaciation, no tili of this stage of the Ice Age was believed to exist in this area. T h e main ice sheet was not believed to have extended m u c h south of Hunstanton, and this is probably true. T h e r e is, however, very good reason to think the snowfields in Sutfolk accumulated to such a thickness that small glaciers cut Channels in the valley slopes through the soft local rocks, forming a tili of local materials. A long trench f r o m Belstead Brook to Stone Lodge cut through a n u m b e r of t h e s e minor glacial C h a n n e l s , some only twelve feet wide, whereas one was over two h u n d r e d yards in width. T w o similar glaciers passed down f r o m Belstead Road ; one was exposed in the sewer t r e n c h e s at Maidenhall, the other when the new Ash Pit at the Railway Locomotive Yard was being excavated.

Consideration of the evidence f r o m various sources and the existence of the buried Channel, some seventy feet deep, suggests the following picture of the landscape of South-East Suffolk :— the N o r t h Sea bed was dry, forming a piain over which the hairy e l e p h a n t s and other animals roamed. T h e i r bones are frequently

BARK

OF A N C I E N T FIELD

LILAC

VOLES AT

T R E E EATEN A W A Y

BY

MARLESFORD.

D. jf. H.

Maclennan.

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BOBBITT'S HOLE, BELSTEAD

brought up in the trawls of fishermen. What is now the estuary of the Orwell was a long narrow glacial lake which became silted up ; nine feet of peat with an abundance of hazel nut shells prove this. The Belstead Brook and other side Valleys were arms of the Orwell Lake ; this is shown by the Bobbitt's Hole excavations, and diggings in other suitable places would doubtless yield further evidence. The terminal moraine of the Orwell glacier must have been beyond the present coastline, possibly on the site of the bar which exists across the mouth of Harwich Harbour.

This moraine would have been subjected to a great deal of erosion when the North Sea submerged the former piain, and it must have been further reduced by tidal scour after the estuaries became tidal.

When completed, the results of the examination of the pollen grains and of the mollusca will appear in a later issue of these proceedings.

[Ed. These important discoveries have come about through watching digging of sewer trenches and other excavations. If members would report any diggings they see other important information may come to light.]

RED CRAG AT

BY F . H . A .

SHELLEY

ENGLEHEART.

IT is well known that the Suffolk Red Crag west of Ipswich is in general much less fossiliferous than that to the east, the deposits having been largely decalcified through dissolution of the shells by acidified water. This process, however, was far from universal, and some years ago I came across a small exposure of fossiliferous crag at Shelley, south of Hadleigh. Unable to follow up the matter at the time, I recently re-visited the place. Only two small patches are now visible—on the hillside above Shelley Hall, about level with the chimneys. Although this area is considerably contorted (see Mem. Geol. Surv. 1885 (10), p. 21) it seems probable that the bed is in situ and not an erratic. All the shells, however, are broken up ; I was able to recognise only Glycimeris [Pectunculus] glycimeris, Linn., cf. Mya arenaria var. lata (J. Sow.), cf. Nucella [Purpura] lapillus (Linn.), cf. Bulla sp. and a small longitudinally ribbed ostreid.

The area is a steep hillside and the " rock " mostly hidden under pasture. Marks just above indicate old quarrying Operations.

These may have been for the overlying gravel or for calcium and phosphate from the crag. Shells may have been abundant. Is it fanciful to suggest that this may possibly have given the parish its name ?