A CLASSIC CASE OF CONFIRMATION BIAS
BILL SAUNDERS
The Origin of the Norfolk Broads - a classic case of Confirmation Bias
mallards
"Broads are shallow reed fringed lakes which originated as great pits dug for peat. In the 14th century these peat diggings flooded . . ."
The Broads Authority
Ormesby Little Broad
"Broads are shallow reed fringed lakes that originated as great pits dug for peat. In the fourteenth century these peat diggings flooded . ."
The Broads Plan 2004, The Broads Authority
If they flooded in the fourteenth century, that means conversely that the diggings had not flooded in earlier centuries.
Question: Why not? Vast quantities of peat were dug up from deep in the fen during the twelfth and thirteenth centuries making the excavations bigger and bigger and bigger, so why did none of them fill up with water until the fourteenth century? Were conditions much drier? Or did the makers of the broads have some means of keeping the diggings dry?
The authorities have speculated about this at some length, but have never been able to provide a definitive answer, certainly not one supported by solid evidence.
There is good reason for their difficulty..
"Their basins must have been formed of undoubted excavations, presumably representing hollows left by deep extraction of peat in historical times, and subsequently flooded after abandonment of the workings. The broads thus formed must at first have been sheets of relatively deep water, bounded by sharp margins of undisturbed deposits." J.M.Lambert, 1952 Presidential Address (text as amended by J.M.L.), Transactions of the Norfolk and Norwich Naturalists Society, Vol. XVII, Soman-Wherry Press, 1956.
The eminent botanist Dr.J.M.Lambert discovered in 1952 that the waters of each one of the Norfolk Broads are confined in a basin which has vertical sides and a level bottom. Beneath their content of water and soft mud, most of these basins are ten or twelve feet deep, some not quite as as deep, a few even deeper. Joyce Lambert deduced that the Broads were not the natural fresh-water lakes that almost everyone, including herself, had supposed them to be.
"Joyce's Eureka moment came late one evening in her study at Cambridge University, where she held a research fellowship at the time. 'The penny,' she said, 'suddenly dropped - the Broads must be man-made. All the anomalies could be explained if they were once the sites of great peat pits which were subsequently flooded.'" "Still Waters", Miles Hedley, Maas, 1999.
With these words and with this concept, Joyce Lambert revealed the true, man-made origin of the Broads, and why men had created them. With these same words and with this same concept, she also advanced a theory of how men had gone about the task: the great pits must have been completely dug out first, only to fill up with water "subsequently".
The theory seemed entirely logical: the broads are huge, flooded pits with vertical sides and level bottoms; peat pits dug by hand with turf-spades or beckets have vertical sides and level bottoms; nobody could have dug peat by hand from the bottom of a deep pit, if they were standing in or submerged beneath several feet of water, so the basins of the broads must have been completely dug out before they became flooded.
Further researches by a number of distinguished people from a variety of academic disciplines then followed Joyce Lambert's initial lead:
"The stratigraphy and the form of the basins in which the broads lie suggest that the Norfolk Broads can only be the product of the large scale extraction of peat, and then the subsequent flooding of the pits thus created." "The historical evidence", C.T.Smith. Part II of "The making of the broads, a reconsideration of their origin in the light of new evidence.", Lambert et.al., R.G.S., 1960.
"Instead, there is now strong reason to believe that the broads themselves are fundamentally artificial features, set in natural surroundings - in other words that their basins represent entirely man-made pits, formed by the deep extraction of peat (presumably for fuel) at some time in the past, and subsequently flooded after the abandonment of the workings." "The origin of the Broads" Lambert, Jennings and Smith, at Chapter 3 of "The Broads", E.A. Ellis, Collins, 1965.
"The main difficulty [with the theory of a man-made origin] lay in understanding how many great peat-cuttings [my italics] to a depth of 10-12ft. or more could have been made in the face of water infiltration." Charles Green, The Times, May 14th, 1956
"The most important tasks of the historical geographer are clearly, then, to establish the period over which the turf-pits were being dug, the dating of the subsequent flooding, and the conditions under which the turf-pits were abandoned." Smith, 1960
They sought, found and interpreted evidence to fit Lambert's theory of how the broads had been created, confirming it with the conclusion that this subsequent flooding of great formerly dry peat pits occurred during the course of the fourteenth century.
Any notion that men might have created these huge peat pits in some other way was initially excluded from everybody's thoughts, and any evidence unfavourable to Lambert's basic concept of how it was done has been insensibly ignored, discounted or misconstrued - a classic example of the phenomenon which behavioural scientists label Confirmation Bias.
Unsurprisingly, the result is an account of the origin of the Norfolk Broads which is itself riddled with anomalies.
Joyce Lambert was herself the first to recognise that her theory raises an important question: if they were dug out first and only flooded subsequently, what had prevented basins of such "sheer size and depth" from filling up with water while the peat was still being extracted?
Over sixty of these peat pits were excavated during the medieval period, all of them down to depths which, as we can now be sure, reached well below the water level in the fens at that time. Starting in the first half of the twelfth century or earlier, the pits were extended over a period of at least three hundred years to a total area of about three thousand acres/twelve hundred hectares. So how exactly had the makers of the broads prevented the pits from filling up with water while they were digging up all this peat before the fourteenth century?
A response to this question has evolved from the collective wisdom of the learned authorities, and has become generally accepted:
"Deep pits excavated in the peat today fill up relatively slowly, and the medieval excavations could probably have been kept dry by regular baling, given sufficient incentive and enough labour." "The Norfolk Broads, a landscape history", Professor Tom Williamson, MUP, 1997
Throughout the long period while the pits were being dug, their entire, ever-expanding area must have been kept dry by (presumably) an ever-increasing number of men wielding an ever-increasing number of bailing devices (for the existence of which in medieval England, as the authorities concede, there is no evidence at all), so that it was not until around the start of the fourteenth century, when their total extent was approaching three thousand acres, that even the smallest part of these vast excavations was allowed to become permanently flooded, "probably".
This despite the fact that the archaeologist, Charles Green, whose professional opinion was originally sought on this very question, took the view that the only way pits as deep as these could have been dug out by hand and expanded to such size was if water levels at the time had been low enough to eliminate the problem of flooding; to have kept pits of this depth dry with any form of pump or bailing device while continually expanding their area was a solution so unlikely as to be incredible.
(Note: The authorities speculate that devices similar to the 19th century ladle-and-gantry were employed, each capable of moving water at the rate of 2,400 gallons per hour. Assuming, without allowing, that this or any other known form of manually operated mechanical bailing device could have raised water out of excavations as deep as those in medieval Broadland [see under "How did they really do it?"], to lower the water-level in a one acre pit by a foot, a ladle and gantry would have to be in continuous operation for 113 hours. Anybody actually taking the trouble to do some calculations about what might constitute "enough labour" will find no difficulty in accepting Charles Green's opinion).
Nevertheless, despite Charles Green's best efforts to persuade us otherwise, it is certain that water levels were not low enough, so how else, it is argued, other than with bailing devices or pumps could all the pits have been kept free of water over a sustained period up to the end of the thirteenth century, if they were only to become flooded "subsequently" in the fourteenth?
A huge and spectacularly rapid rise in the level of the sea was originally hailed as the cause of the flooding. When it became clear that the scale and pace of this rise had been grossly overestimated, the storms and tidal surges associated with a change in the climate were deftly substituted. After all, something must finally have overwhelmed the massed ranks of bailers, whose superhuman efforts had been keeping the waters at bay from deep excavations the size of two thousand football pitches. Why else would all the great pits have been abandoned by the fifteenth century?
The 400+ acres of Hickling Broad - kept dry by "regular baling" until the fourteenth century?
Why do the authorities have this difficulty in explaining how the pits had remained dry before the fourteenth century? The answer is simple: the Norfolk Broads did not originate as "the sites of great peat pits which were subsequently flooded".
They originated as:
quite small, adjacent peat pits, isolated one from another by walls of peat no more than three feet thick;
each pit was abandoned to flood permanently as soon as it had been dug;
these flooded pits were later joined together, creating larger areas of open water.
At the invitation of Miss Marietta Pallis, Joyce Lambert herself witnessed this method being put into practice in September, 1953. Adjacent pits were dug in the peat fen to a depth of ten feet, and joined together to create a unique design of pool three quarters of an acre in extent; the task was carried out by a gang of four men, working intermittently over a period of nearly three months; they used only hand tools, including those traditional to the Broadland fens and marshes; the limited amount of bailing necessary was done with hand-held scoops and buckets; they had no pumps nor other devices alien to medieval England (see under "How did they really do it?" and under "Marietta Pallis").
The renowned 'Broadsman' and conservationist, Dr. Martin George, O.B.E., devoted a chapter of his great work "The Land Use, Ecology, and Conservation of Broadland" (Packard, 1992) to the origin of the broads, and provided some significant additions to the already established speculation about how they had been created (see under "How Joyce Lambert's concept was developed"); he correctly deduced that
" . . . some sort of baling technique would probably have proved effective, provided the diggings were fairly small [my italics], and were kept isolated from their neighbours by baulks",
and that, with this method,
" . . . there seems no reason why it [peat] could not have been dug to a depth of 3 m or more, even if the water table was quite near the surface".
In attempting to perpetuate Lambert's concept of "subsequent" flooding, however, George missed the logical consequence of his small, isolated diggings: each one would have been abandoned to flood permanently as soon as it was completed, so the turf-pits cannot all have flooded in the fourteenth century. George seconded Joyce Lambert in the use of the ladle and gantry (". . although there is no evidence that this device was ever used in Broadland . ."), but was clearly unaware that his thesis of small, separate pits had already been put into practice successfully in 1953, with no more elaborate a "baling technique" than hand-held scoops and buckets. No machina ex deo was required.
The impossible having been eliminated, the only remaining method by which the broads could have been created under the conditions now known to have prevailed in the medieval period is the "medieval method - the obvious one" ("The impermeability of peat and the origin of the broads", M. Pallis, Glasgow, 1956) devised by Marietta Pallis; it is, therefore, the method which must have been used. Each small pit would have been abandoned to flood permanently as soon as it was completed, so it cannot be the case that none of the turf-pits flooded before the fourteenth century.
Joyce Lambert's basic concept of "great peat pits which were subsequently flooded" has taken precedence, but, in developing it, much evidence has been insensibly twisted or ignored. This website shows how this same evidence, and more, can and should be interpreted very differently.
"How Joyce Lambert's concept was developed." HOME
Copyright 2009 The Medieval Making of the Norfolk Broads. All rights reserved.
The Origin of the Norfolk Broads - a classic case of Confirmation Bias
mallards