Steenbergen, a town rebuild on zel-as
The explored terrain measured about 50 by 20 meters. At first it looked as if it was like every parcel after demolition of a building (as was indeed the case). But, on closer inspection the "soilmaterial" was mostly something else. It was a crumbling mixture of smaller and greater pieces of a soft white-gray stuff with very black inclusions and shell-fragments. It desintegrated under a light pressure. As such it could readily be distinguised from the hard, gray, "young" looking debris of the demolished building. On the terrain also lose shell-fragments, lose little clumps of black material and unrecognisable pottery-remains were found. Digging revealed that this layer was here at least 50 cm thick. It bordered on the mediaeval harbour.
At later occasions G.C. Groeneweg, a local archaeologist, has explored a lot of gardens in the town centre. So he got the impression that the whole of the medieval towncentre (400 by 300 meters) is build on or in this 50 - 100 cm thick layer. Still later an early 14th century brick house (mentioned in texts from 1327-1339 as standing) were excavated. It was not build on this layer, but at a later moment the layer was spread against the lower part of the building.
Steenbergen began around 1263 - 1267 as a saltmaking place with a harbour and sailers that took part in the wooltraffic between the Low Countries and England. Around 1330-40 it became a town and in 1366 it burned down. MAP ca. 1360 The place was rebuild on a smaller scale. We think that the ash-layer was carried from the salt-making places into the burned-down town to rise the new town just that little bit, that it was safe for the rising tides of that period (see lower). So the ash-layer would be of shortly after 1366.
Analysis of the "zel as"
Three samples of the "zel as" were analysed by X-ray-diffraction and chemical analysis. This was done by Dr. Ir. Breeuwsma of the then "Stichting voor Bodemkartering" (now: Staring Centre) at Wageningen, The Netherlands. He writes (nov. 6, 1981):
According to the analysis the samples consist for 40 - 50 % of CaCO3 and CaMgCO3. Also present is quartz, feldspar and mica. Further diopsite, CaMg(SiO3)2, SiO2, Fe2O3 and Fe3O4. The samples were characterized by a high glowing-loss, probably indicating charcoal-rests. No aluminiumsilicates were detected. This indicates that the basis-material contained nearly no clay. The presence of feldspar and quartz means that sand was present.
The colors are "pure" or a mixture of
white: diopsite, CaCO3, CaMgCO3
red: Fe2O3, Fe3O4
black: charcoal
According to Breeuwsma the material is formed at temperatures between 500 and 1000 Celsius.
Information about the landscape
First it is important to see what landscape surrounded Steenbergen between 1263 - 1366. The town itself sits on the last spur of "high" sandy soils, that is between 1 and 3 m above sealevel. At least 300 degrees around were peatsoils: the very rim of the great "Holland-peat" district of the coastal plain of the Netherlands. To the west lies Zeeland, a province through which long arms of the sea developed during earlier centuries. Along this expanding sea-arms the salty water could eventualy reach Steenbergen from probably around 1260 onwards. As the sea-arms gradually lengthened and deepened, the tide-amplitude at Steenbergen increased and the salt water reached further inland.
No major rivers discharged near to Steenbergen. The river Sceldt had only a narrow and shallow connection to this region and the river Meuse didn't come closer than 25 km, after 1283 even 30 km. Only a small local river or brook ran along the town.
So the circumstances were good for drowning the peat with salt water, without to much fresh water from inland sources. The deposition of a clay-layer of any importance didn't yet go very fast in this period. This is also seen some 25 km further north, were between 1288 and 1421 (133 years) only some decimeters clay were deposited, and between 1421 and ca. 1560 (139 years) between 1 and 2 meters in polders next to the first one ! Only after 1421 the Meuse and Rhine rivers could bring sediment into this region.
Interpretation
The Steenbergen saltworks were situated in the rim of a peatfilled floodplain, 40 to 45 km from the coast, but connected with the sea by the sea-arms of Zeeland. No major freshwater rivers discharged in the direct vincinity. The analysed ashes underlie the town that was rebuild after 1366. As Steenbergen probably began 1263 - 1266, we can suppose that the ashes were formed between 1263 - 1366. In this period the claylayer on the peat around Steenbergen was only slowly sedimentated. Perhaps this still only shallow clay-layer makes clear why the early (1263 - 1366) Steenbergen-ashes do not show te use of clay. But then, the pottery-fragments (probably the briquetage) were NOT analysed !
Interesting is that no sulphates did show up in the ashes (See the communication by Beatrice Hopkinson on this list).
Literature
