|
A geophysical survey of the Caergwanaf uchaf site (Young 2000) revealed a complex of anomalies over an area of 3.5ha. The main part of the site was interpreted as an ironworks of mid C16 date, with three hand-blown bloomery furnaces on the terrace slopes and with a pond, fed by springs, supplying water to a water-powered forge on the floodplain below. The survey also extended over the adjacent low hill, and unexpectedly, showed evidence for a second cluster of furnaces on the crest of the hill, associated with a rectilinear ditched enclosure system and a scatter of Romano-British pottery in association with a spread of bloomery slag. Subsequent fieldwork (spring 2002) has demonstrated that this scatter of slag apparently continues to the south of the M4 embankment over 300m to the south.
The 2000 report is available in 3 sections: text (0.1 Mb), figs 1-4 (6 Mb) and figs 5-9 (6 Mb).
The abstract of the survey report (Young 2000) stated:
An area of approximately 3.5 hectares in a field (Field A) between the farm of Caergwanaf uchaf and the Elai (centred on NGR [ST 045807]) was surveyed using an FM36 magnetic gradiometer and an MS2 magnetic susceptibility meter. A smaller part of the field was also surveyed with an RM4 ground resistivity meter. Part of a second field (Field B) lying adjacent to Field A on the floodplain of the Elai was also surveyed with the MS2. The topography of a wider area including both fields was surveyed by EDM, and part of the floodplain was surveyed with an EM31 ground conductivity meter.
The results suggest the presence of two iron making complexes within the survey area. That in the lower part of Field A , the original target of this survey, is interpreted to be of sixteenth century date, with two or three smelting furnaces and a probable water-powered bloom smithy. The anomalies interpreted as smelting furnaces are situated on the steep slope a few metres above the level of the flood plain, and must therefore have been manually blown. The slag dumps extend over at least 4,500 m2. Water power may have been provided by a spring-fed pond, which partially survives in Field B.
The second site is smaller, and lies on the crest of the ridge in the upper part of Field A. The gradiometer results show several circular anomalies in the area, which are tentatively identified as hearths or furnaces. This upper part of Field A also shows a partly rectilinear system of lower magnitude gradiometer anomalies, apparently a system of enclosures. At the western edge of the survey a square feature 10m wide is oriented parallel to the probable field boundaries. The topsoil of this upper part of the field, particularly its southern half, yields abundant iron slags, both tap slags and smithing slags, and several sherds of Romano-British pottery were recovered during the geophysical survey and subsequently after ploughing. A Roman age is thus tentatively ascribed to this second site.
 |
 |
Figure 1. Magnetic gradiometer survey (Geoscan FM36) of the Caergwanaf uchaf site. North to the right. Survey undertaken with 1.0m traverse interval and 0.5m sample interval. Dark green = -10nT, white = +10nT. This scale reveals the low amplitude features more clearly. |
Figure 2. Magnetic gradiometer survey (Geoscan FM36) of the Caergwanaf uchaf site as figure 1, but displayed with dark green = -10onT, white = +100nT. This scale reveals the large amplitude features more clearly. |