South Wales Gas Pipeline Project Land East of Rose Hill · 2016-10-27 · South Wales Gas Pipeline Project Site 257 Land East of Rose Hill Rosemarket . Pembrokeshire Archaeological

South Wales Gas Pipeline Project Site 257

Land East of Rose Hill Rosemarket

Pembrokeshire

Archaeological Watching Brief

October 2013

for

on behalf of Rhead Group

National Grid CA Project: 9150

CA Report: 13208 Event: DAT108825

South Wales Gas Pipeline Project Site 257

Archaeological Watching Brief

CA Project: 9150 CA Report: 13208 Event: DAT102846

prepared by Peter Busby, Project Supervisor

date 17 October 2013

checked by Karen E Walker, Post-Excavation Manager

date 27 May 2015

approved by Martin Watts, Project Director, Head of Publications

signed

date

issue 01

This report is confidential to the client. Cotswold Archaeology accepts no responsibility or liability to any third party to whom this report, or any part of it, is made known. Any such party relies upon this report entirely

at their own risk. No part of this report may be reproduced by any means without permission.

© Cotswold Archaeology

Cirencester Milton Keynes Andover Building 11 Unit 4 Office 49 Kemble Enterprise Park Cromwell Business Centre Basepoint Business Centre Kemble, Cirencester Howard Way, Newport Pagnell Caxton Close, Andover Gloucestershire, GL7 6BQ MK16 9QS Hampshire, SP10 3FG t. 01285 771022 t. 01908 218320 t. 01264 326549 f. 01285 771033

e. [email protected]


1

South Wales Gas Pipeline Project Site 257: Archaeological Watching Brief

CONTENTS

SUMMARY ..................................................................................................................... 2

1. INTRODUCTION ................................................................................................ 3

The site .............................................................................................................. 3

Archaeological background ................................................................................ 4

Archaeological objectives ................................................................................... 4

Methodology....................................................................................................... 4

2. RESULTS (FIG. 2) ............................................................................................. 5

3. PROJECT TEAM ............................................................................................... 7

4. REFERENCES ................................................................................................... 8

APPENDIX A: CONTEXT DESCRIPTIONS .................................................................... 10

APPENDIX B: THE FINDS .............................................................................................. 12

LIST OF ILLUSTRATIONS Fig. 1 Site location plan (1:25,000)

Fig. 2 Plan showing archaeological features (1:200)

GLOSSARY CA – Cotswold Archaeology

CAP – Cambrian Archaeological Projects

CPAT – Clwyd Powys Archaeological Trust

DAT – Dyfed Archaeological Trust

GGAT - Glamorgan Gwent Archaeological Trust

FTP – Felindre to Brecon gas pipeline

HER – Historic Environment Record

MHA – Milford Haven to Aberdulais gas pipeline

NAL – Network Archaeology Ltd

NLMJV – Nacap Land & Marine Joint Venture

UPD – Updated Project Design


2


SUMMARY

Project Name: South Wales Gas Pipeline Project

Location: Site 257, Land East of Rose Hill, Rosemarket, Pembrokeshire

NGR: SM 9421 0928

Type: Watching Brief

Date: 12–14 July 2006

Location of Archive: To be deposited with RCAHMW (original paper archive) and Scolton

Manor Museum (digital copy of paper archive; accession number

2008.1)

Site Code: MHA06

An archaeological watching brief was undertaken by Cotswold Archaeology during

groundworks associated with construction of gas pipelines (part of the South Wales high

pressure gas pipeline scheme) between Milford Haven and Aberdulais, and Felindre and

Brecon, which were conducted between 2005 and 2007.

The watching brief recorded a possible enclosure and pits, as well as evidence for metal

processing. The features were poorly defined, only limited dating evidence was recovered

and only part of the activity was exposed. The metalworking technology revealed is dateable

to the Roman or medieval periods and the only other find comprised a Roman tile fragment.

Based on this, it is tentatively suggested that part of a Roman site was exposed. The

evidence from the metallurgical residues was suggestive of primary iron production; however

there was no archaeological evidence that any furnaces or industrial structures had existed

within the site itself. Two later, but undated, gravel extraction pits were also found.


3


1. INTRODUCTION

1.1 NACAP Land and Marine Joint Venture (NLMJV), on behalf of National Grid,

commissioned RSK Environment (part of the RSK Group) to manage the

archaeological works (non-invasive surveys, desk based assessment, evaluation,

watching brief, and open area excavation) on a 216km-long section of pipeline from

Milford Haven (Pembrokeshire) to Brecon (in Powys). The high pressure gas

pipeline (part of the 316km-long pipeline route from Milford Haven to Tirley in

Gloucestershire) was required to reinforce the gas transmission network. The

archaeological work performed in advance of this pipeline was undertaken in a

number of sections by a number of archaeological companies. The westernmost

section of 122km, from Milford Haven to Aberdulais, was investigated by CA (then

Cotswold Archaeological Trust) during 2005–2007 with some additional excavation

work carried out by CAP. The section of 89km, from Felindre to Brecon was

investigated by CA during 2006–2007 and CAP during 2007. Assessment reports on

the works were completed in January 2012 (NLM 2012a, 2012b) and the current

reporting stage was commissioned in February 2013.

1.2 Between 12–14 July 2006 CA carried out an archaeological watching brief at Site

257, Land East of Rose Hill, Rosemarket, Pembrokeshire (centred on NGR: SM

9421 0928; Fig. 1). The objective of the watching brief was to record all

archaeological remains exposed during the pipeline construction.

1.3 The watching brief was carried out in accordance with professional codes, standards

and guidance documents (EH 1991; IfA 1999a, 1999b, 2001a, 2001b and IfA Wales

2008). The methodologies were laid out in an Archaeological Management Plan

(RSK 2006) and associated Written Statements of Investigation (WSIs) and Method

Statements.

The site 1.4 The site is located within a field on the northern slopes of a 60m AOD-high hill,

overlooking a tributary of the Westfield Pill (Fig. 1). It lies at approximately 50m

AOD. The underlying solid geology of the area is mapped as the Rosemarket

Formation of the Silurian Period; no superficial deposits are recorded (BGS 2013).


4


Archaeological background 1.5 No archaeological remains were identified within the site during the preliminary

Archaeology and Heritage Survey (CA 2005). However, Clareston Maenhir, a

Bronze Age or post-medieval standing stone (PRN 2374), and an unnamed burnt

mound (PRN 3171) are located 1km north-east of the site. Rosemarket Rath, an Iron

Age defended enclosure is also recorded 1.6km south-east of the site (PRN

305262).

1.6 Archaeological investigations during the construction of the pipeline recorded

remains within the vicinity of Site 257 (Fig. 1). These included three Late Neolithic

pits at Site 272, an undated oven/furnace at Site 258 and two undated pits with

charcoal-rich fills at Site 271 (CA 2013 a, b and c).

Archaeological objectives 1.7 The objectives of the archaeological works were:-

• to monitor groundworks, and to identify, investigate and record all significant buried

archaeological deposits revealed on the site during the course of the development

groundworks; and

• at the conclusion of the project, to produce an integrated archive for the project work

and a report setting out the results of the project and the archaeological conclusions

that can be drawn from the recorded data.

Methodology

1.8 The fieldwork followed the methodology set out within the WSI (NLM 2006). An

archaeologist was present during intrusive groundworks comprising stripping of the

pipeline easement to the natural substrate (Fig. 1).

1.9 Where archaeological deposits were encountered written, graphic and photographic

records were compiled in accordance with CA Technical Manual 1: Fieldwork

Recording Manual.

1.10 The archaeological features recorded were poorly defined due to the nature of the

gravel substrate and their edges were not established with any great certainty. For

this reason, not all of the features are described in detail below and no section

drawings are included. Details are however presented in Appendix A.


5


1.11 The post-excavation analysis and reporting work was undertaken following the

production of the UPD (GA 2012) and included re-examination of the original site

records and Finds, evidence was taken from the assessment reports (NLM 2012a)

except where the UPD recommended further work, in which case the updated

reports were used. The archaeological background to the site was assessed using

the following resources:-

• the Archaeology and Heritage Survey which was undertaken in advance of the

pipeline construction and which examined a 1km-wide corridor centred on the

pipeline centre line, including the then existing HER record (CA 2005);

• Dyfed Archaeological Trust HER data (received May 2014); and

• other online resources, such as Google Earth and Ordnance Survey maps

available at http://www.old-maps.co.uk/index.html.

All monuments thus identified that were relevant to the site were taken into account

when considering the results of the fieldwork.

1.12 The archive and artefacts from the watching brief are currently held by CA at their

offices in Kemble. Subject to the agreement of the legal landowner the artefacts will

be deposited with Scolton Manor Museum under accession number 2008.1 along

with a digital copy of the paper archive. The original paper archive will be deposited

with the RCAHMW.

2. RESULTS (FIG. 2)

2.1 This section provides an overview of the watching brief results; detailed summaries

of the recorded contexts and finds are to be found in Appendices A and B. Full,

original versions of the specialist reports are available within the archive. The natural

geological substrate (257002), comprising pale silty sand and gravel, was cut by

ditches and pits.

Roman

2.2 Two ditches (257017 and 257031) forming part of a possible enclosure were found

at the eastern end of the site. Their northern extents were truncated by a gravel

extraction pit but the possible enclosure would have been 7m wide and included a

possible south-east facing entrance. The ditches themselves were up to 1.15m wide

http://www.old-maps.co.uk/index.html


6


and 0.15m deep and contained homogenous silty clay fills. Ditch 257031 contained

a piece of Roman imbrex tile and a tiny piece of slag (Appendix B).

2.3 To the west of the possible enclosure were a number of pits and postholes. Although

undated by finds, the larger of these features conformed to the alignment of the

possible enclosure and several were also truncated by gravel extraction pits. For

these reasons, these features have been assigned to the Roman period, although

this dating should be regarded as tentative.

2.4 Amongst these features were several oval to sub-rectangular pits (257009, 257013,

257019, 257021 and 257049). These were up to 5.2m long, 1.4m wide and 0.6m

deep with generally steep sides and flat bases. All contained silty clay fills and finds

from these were restricted to a fragment of weathered slag, probably from a smithing

hearth cake, from the fill of pit 257013 (Appendix B). A further rectangular pit

(257025) was found but not located on plan. Its fill contained fragments of smithing

hearth cake (Appendix B).

2.5 The remaining features comprised small oval pits (257005, 257007 and 257033) and

features described as postholes, but which might equally have been small pits

(257003, 257023, 257029, 257035, 257037, 257039, and 257041). All contained

undated silty clay fills.

Post-Roman

2.6 Two large gravel extraction pits (257043 and 257025) were located at the western

and eastern ends of the site respectively. These were both large, amorphous,

shallow features, neither more than 0.25m deep with gently sloping sides and

irregular, uneven bases. Fragments of slag derived from primary ironworking

activities were recovered from these features but these were probably residual from

the earlier features which had been truncated by the extraction pits (Appendix B).

Discussion

2.7 Although the remains on site were poorly dated, the presence of the Roman tile

fragment and of slag dateable to the Roman to medieval period (see Appendix B)

hints that the earliest features were probably Roman. The imbrex tile may indicate

that a substantial building was present close to the site.


7


2.8 The archaeometallurgical evidence is highly indicative of a primary iron production

site, undertaking both bloomery iron smelting using a slag-tapping furnace and

bloom processing (Appendix B). Despite this no hammerscale was recovered from

the site; had it been present, this would have implied that metal processing had

occurred on the site itself since hammerscale tends to remain close to the point of

origin. It is less easy to be certain about the provenance of larger slag pieces, and

those found on site might either relate to processes occurring in the immediate

vicinity or have been imported incidentally or for re-use (for example as hardcore).

No furnaces were present within the excavated area, and none of the feature fills

were indicative of furnace debris so if any metal processing was occurring, then the

exposed remains must have been located away from this. The majority of slag

fragments were derived from gravel extraction pit 257043 and were probably not in

their primary depositional contexts.

2.9 The gravel extraction pits were undated, other than perhaps being post-Roman.

3. PROJECT TEAM

Fieldwork was undertaken by Kelly Saunders, assisted by Sian Reynish, Carina

Summerfield and Richard Watts. This report was written by Peter Busby with

comments by Jonathan Hart and illustrations prepared by Daniel Bashford. The

archive has been compiled by Jonathan Hart, and prepared for deposition by Hazel

O’Neill. The fieldwork was managed for CA by Clifford Bateman and the post-

excavation work was managed for CA by Karen Walker.


8


4. REFERENCES

BGS (British Geological Survey) 2013 Geology of Britain Viewer. Online resource at

http://mapapps.bgs.ac.uk/geologyofbritain/home.html accessed 21 June 2013

CA (Cotswold Archaeology) 2005 Milford Haven to Aberdulais Gas Pipeline: Archaeology

and Heritage Survey. CA typescript report 04147 CA (Cotswold Archaeology) 2013a South Wales Gas Pipeline Project. Site 272 Land West of

Westfields, Rosemarket, Pembrokeshire: Archaeological Watching Brief. CA

typescript report 13214 CA (Cotswold Archaeology) 2013b South Wales Gas Pipeline Project. Site 258 Land East of

Rushmoor, Rosemarket, Pembrokeshire: Archaeological Watching Brief. CA

typescript report 13209 CA (Cotswold Archaeology) 2013c South Wales Gas Pipeline Project. Site 271 Land North

of Westfields, Rosemarket, Pembrokeshire: Archaeological Watching Brief. CA

typescript report 13213 Crane, P. and K. Murphy 2010 ‘Early medieval settlement, iron smelting and crop processing

at South Hook, Herbranston, Pembrokeshire, 2004–05’, in Archaeologia

Cambrensis, 159, 117–196

GA (Groundwork Archaeology) 2012 Milford Haven to Aberdulais and Felindre to Brecon

High Pressure Gas Pipelines: Updated Project Design

Hall, R. 2008 ‘Assessment Report for Ceramic Building Material’, in NLM 2012a

IfA (Institute for Archaeologists) 1999a Guidelines for Finds Work. IfA, Birmingham

IfA (Institute for Archaeologists) 1999b Standard and Guidance for Finds and Ecofact

Studies and Curation. IfA, Reading

IfA (Institute for Archaeologists) 2001a Standard and Guidance for the Collection,

Documentation, Conservation and Research of Archaeological Materials. IfA,

IfA (Institute for Archaeologists) 2001b Standard and Guidance for an Archaeological

Watching Brief

IfA Wales (Institute for Archaeologists of Wales/Cymru) 2008 Introducing a Research

Framework for the Archaeology of Wales, online resource at

http://www.archaeoleg.org.uk/intro.html accessed December 2008

NLM (Nacap Land and Marine) 2006 Milford Haven to Aberdulais Natural Gas Pipeline:

Scheme of investigation for a programme of archaeological works

NLM (Nacap Land and Marine) 2012a Milford Haven to Aberdulais High Pressure Gas

Pipeline: Archaeology Assessment of Potential for Analysis

http://mapapps.bgs.ac.uk/geologyofbritain/home.html

http://www.archaeoleg.org.uk/intro.html


9


NLM (Nacap Land and Marine) 2012b Felindre to Brecon High Pressure Gas Pipeline:

Archaeology Assessment of Potential for Analysis

RSK (RSKENSR) 2006 Milford Haven to Aberdulais Natural Gas Pipeline: Archaeological

Management Plan. Nacap Land and Marine Final, RSKENSR Environmental Ltd

Young, T. P 2010a Archaeometallurgical Residues from the South Hook LNG Terminal.

GeoArch Report 2010/03

Young, T. P 2010b Analysis of Archaeometallurgical Residues from Brownslade,

Pembrokeshire [NPRN 94225]. GeoArch Report 2010/07

Young, T. P 2014a Archaeometallurgical Residues from the Milford Haven – Brecon

Pipeline. GeoArch Report 2013/30

Young, T.P 2014 Archaeometallurgical Residues from Dwr-y-Felin School,Neath (GGAT 677

& 716). GeoArch Report 2013-27


10


APPENDIX A: CONTEXT DESCRIPTIONS

Context No.

Fill of Context interpretation

Description L (m)

W (m)

Depth (m)

257000 Topsoil Grey-brown sandy silt 0.15 257001 Subsoil Yellow-brown silty clay 0.20 257002 Natural Light yellow-brown silty sand with frequent

stones

257003 Pit Circular in plan with steep sides and a concave base

0.75 0.2

257004 257003 Pit fill Dark yellow-brown clay silt with frequent stones 0.75 0.2 257005 Pit Oval in plan with shallow sides and a concave

base 1.35 0.55 0.1

257006 257005 Pit fill Dark yellow-brown clay silt with moderate and burnt stones

1.35 0.55 0.1

257007 Pit Oval in plan with shallow sides and a concave base

0.85 0.40 0.1

257008 257007 Pit fill Orange-brown clay silt with stones 0.85 0.40 0.1 257009 Pit Rectangular in plan with steep sides and flat

base 3.7 1.1 0.4

257010 257009 Pit fill Orange-brown silty clay with flecks of charcoal 3.7 1.1 0.4 257011 Pit Part of 257009 257012 257009 Pit fill Yellow-brown silty clay with occasional stones

and charcoal flecks

257013 Pit Sub-oval in plan with steep sides and a flat base 2.5 1.3 0.6 257014 257013 Pit fill Lower fill: dark brown sandy silty clay with

frequent pebbles 0.75 0.25

257015 257013 Pit fill Middle fill: yellow-brown sandy silt with frequent stones

0.85 0.2

257016 257013 Pit fill Upper fill: dark grey-brown sandy silt with frequent small stones

1.35 0.25

257017 Ditch Irregular curvilinear cut in plan running 1.5m N/S then turning through 90° and running for a further 4m before terminating. It had a V shaped profile

6.5 0.45 0.15

257018 257017 Ditch fill Orange-brown clay silt with occasional charcoal flecks

6.5 0.45 0.15

257019 Pit Sub-oval in plan with moderately sloping sides and a flat base

5.2 0.7 0.15

257020 257019 Pit fill Grey-brown clay silt with pebbles 5.2 0.7 0.15 257021 Pit Square in plan with shallow sides and irregular

base 1.65 1.4 0.2

257022 230021 Pit fill Yellow-brown silty clay with occasional charcoal flecks and stones

1.65 1.4 0.2

257023 Pit Oval in plan with steep sides and a pointed base 0.35 0.25 0.25 257024 230023 Pit fill Dark grey-brown clay with charcoal flecks,

stones, burnt clay flecks, and burnt stones 0.35 0.25 0.25

257025 Extraction pit Sub-rectangular in plan with rounded corners, steep sides and a flat base

8.3 5.0 0.35

257026 257025 Pit fill Brown sandy silt with occasional stones 8.3 5.0 0.35 257027 Posthole Circular in plan with steep sides and concave

base 0.25 0.2 0.2

257028 257027 Posthole fill Brown silt with occasional small to medium stones

0.25 0.2 0.2

257029 Pit Circular in plan with moderately sloping sides and concave base

0.7 0.6 0.05

257030 257029 Pit fill Yellow-brown clay silt with stone, charcoal flecks and burnt stones

0.7 0.6 0.05

257031 Ditch N/S aligned with a shallow U-shaped profile and a rounded base

5.0 1.15 0.15


11


257032 257031 Ditch fill Yellow-brown clay silt with pebbles and charcoal flecks

5.0 1.15 0.15

257033 Pit Oval in plan with moderately sloping sides and a rounded base

0.95 0.35 0.15

257034 257033 Pit fill Dark brown-grey silty clay with charcoal flecks and stones

0.95 0.35 0.15

257035

Posthole Circular in plan with irregularly sloping sides and a concave base

0.25 0.1

257036 257035 Posthole fill Dark brown-grey silty clay with stones and charcoal flecks

0.25 0.1

257037 Posthole Circular in plan with shallow sides and concave base

0.3 0.05

257038 257037 Posthole fill Orange-grey-brown silty clay with stones and charcoal flecks

0.3 0.05

257039 Posthole Circular in plan with shallow sides and concave base

0.35 0.05

257040 257039 Posthole fill Dark grey-brown silty clay with stones and l charcoal flecks

0.35 0.05

257041 Posthole Oval in plan with shallow sides and irregular base

0.35 0.25 0.05

257042 257041 Posthole fill Dark orange-grey-brown silty clay with stones and charcoal flecks

0.35 0.25 0.05

257043 Extraction pit Sub-rectangular with gently sloping sides and an irregular base

4.5 3.75 0.25

257044 257043 Pit fill Grey-brown silty clay with sub-angular stones 4.5 3.75 0.25 257045 Ditch Same as 257017 6.5 0.45 0.15 257046 257045 Ditch fill Same as 257018 6.5 0.45 0.15 257047 Extraction

Pit Same as 257025 8.3 5.0 0.25

257048 257047 Pit fill Same as 257026 8.3 5.0 0.25 257049 Ditch Square terminus of a N/S orientated ditch. Steep

sides and a flat base 3.1 1.55 0.25

257050 257049 Ditch fill Orange-brown silty clay with stones 3.1 1.55 0.25 257051 Pit Part of pit 257013 0.38 0.1 257052 257051 Pit fill Lower fill: dark orange-brown silt with charcoal

flecks and stones 0.38 0.1

257053 257051 Pit fill Upper fill: light grey-blue granite boulder 0.38 0.1 257054 Pit Same as 257025 8.3 5.0 0.35 257055 257054 Pit fill Same as 257026 8.3 5.0 0.25 257056 Posthole Oval in plan with steep sides and concave base 0.25 0.2 0.15 257057 257056 Posthole fill Dark yellow-brown clay silt with charcoal flecks 0.25 0.2 0.15 257058 257005

Pit fill Upper fill: brown silty sand with stones 8.3 3.5 0.35


12


APPENDIX B: THE FINDS

Finds concordance (Hall 2008 and Young 2011)

Context Description Count Weight (g) Spot date 257 u/s Slag (weathered slag, variably vesicular,

angular fragment similar to those from 257001)

1 2

Subsoil 257001 Slag (fragmented iron slags, ranging from pieces with moderately-sized charcoal moulds through to dense slags probably from core of an SHC) Slag (small fragments of slag formed of small lobes with charcoal moulds, largest piece may suggest that these are fragments of a slag rod/runner/spike)

29+

6

186

34

Roman– medieval

Pit fill 257014 from pit 257013

Slag (fragment from margin of SHC with tubular vesicles in lower crust, very weathered)

1 (4) 84 Roman– medieval

Pit fill 257026 from pit 257025

Slag (grey vesicular slag fragments, all probably from SHCs)

8+ 84 Roman– medieval

Ditch fill 257032 from ditch 257031

CBM (imbrex tile with incised diagonal lines) Slag (tiny chip of charcoal-rich slag)

1

1

126

2

Roman

Extraction pit fill 257044 from pit 257043

Slag (216g: piece from bowl of SHC, concavo-convex, steep side with slightly hematised surface on interior, over 15mm thick bladed fayalite, outer few mm finer, grading into rough outer surface; 90g: 2 conjoining pieces of dense)

8 454 Roman– medieval

SHC= Smithing hearth cake

Metal Residues (Young 2014a)

Introduction

Site 257 (SM 94209 09279) lies approximately 1km east of Johnston, and approximately 0.3km north of

Bastleford (NLM 2012a).

The site included a number of pits and ditches, which were all undated, except for the occurrence of a single

fragment of Roman imbrex roof tile in one ditch terminus.

Four representative pieces were selected for further investigation (MHB1 – 4), all from fill 257044 of gravel

extraction pit 257043 (similar material was also present in the archive from subsoil 257001, pit fills 257014 and

257032 and from ditch fill 257026).

Results Distribution of materials

This site produced 53 pieces of iron slag (844g) from five stratified contexts (257001, 257014, 257026, 257032,

257044) and one unstratified piece (2g). The majority of the pieces are either certainly or probably fragments

from smithing hearth cakes (SHCs) but a small proportion appear likely to be bloomery smelting slags from a

slag-tapping furnace.


13


The slag-tapping nature of the smelting operation is suggestive of either a Roman or later medieval (post-ninth

century) age for this activity.

Description of materials

General

The specimens of slag selected for further analysis included:

MHB1; SHC fragment with bladed olivine below a glassy top

MHB2; a dense but weathered burr(?) from a SHC

MHB3; a hollow, tapslag like nub of flowed slag

MHB4; a tapslag fragment

The two smelting slag specimens (MHB3 and MHB4) were both very iron-rich (77% and 78%, expressed as wt%

FeO respectively), producing a wustite-dominated microstructure. They both showed elevated manganese

contents (1.4% and 3.4% expressed as wt% MnO respectively), reflected in substantial substitution of

manganese into the fayalite (typically 7% and 11% respectively). The mineralogy was simple, with primary

wustite followed by fayalite, of which the main generation of elongate crystals were prolonged into fine quenched

dendrites in the interstitial glass. Barium was low, as was phosphorus (0.69% and 0.46%, expressed at wt%

P2O5). They showed a low content of thorium (1.4 and 2.0ppm) and a moderate content of uranium (10.5 and

18.7ppm) giving a U:Th ratio of 7.2 and 9.3 respectively. Rare earth element concentrations were also moderate

(total REE of 131ppm and 122ppm). Their Upper Crust normalised REE profiles are gently inclined (Figure 1),

with the LREE relatively depleted, the MREE to HREE fairly flat.

The iron-working slags were represented by MHB1, a coarsely crystalline slag ‘puddle’ and MHB2, probably the

‘burr’ region of an SHC. MHB1 showed a strong compositional gradient from an iron-rich basal section into a

silicate rich upper part with long bladed olivine crystals. MHB2 was slightly more homogeneous. The two samples

had lower bulk iron contents than the smelting slags (66% and 72% expressed as wt% FeO respectively). In the

base of MHB1, the iron content was strongly gradational, with a basal section of up to 88% (expressed as wt%

FeO) and an upper section with 54-85% (on the same basis). MHB2 had a microstructure of wustite, followed by

fayalite with 7-9% manganese substitution, which extended into quenched dendritic structures within the

interstitial glass. MHB1 showed a more variable paragenesis, with the lower part showing primary wustite, the

upper primary fayalite. The fayalite typically showed 4-5% manganese substitution. The interstitial areas showed

a complex groundmass involving leucite, fayalite and wustite.

For the iron-working slags, barium was low, but higher than in the smelting slags (160 and 162ppm). Phosphorus

was also low (0.55% and 0.59%, expressed at wt% P2O5). They showed a low content of thorium (3.2 and

2.1ppm) and a low content of uranium (5.0 and 4.4ppm) giving a U:Th ratio of 1.6 and 2.1 respectively, much

lower than for the smelting slags. Rare earth element concentrations were also low (total REE of 64ppm and

80ppm). Their Upper Crust normalised REE profiles are parallel to those of the smelting slags, being gently

inclined, with the LREE relatively depleted, the MREE to HREE fairly flat.


14


Sample details

MHB1

This sample was taken from the bowl of the largest SHC fragment (a 216g piece from pit fill 257044) which

showed an interesting morphology, with a strongly concavo-convex profile, a haematised upper surface and with

much of the thickness of the slag in the bowl being formed of bladed olivine with individual crystals having lengths

of 15mm or more. These features indicate the existence of a significant molten slag puddle and are possibly

associated in some instances with SHCs generated during bloom-remelting rather than simply during forging

operations. The outer surface of the bowl is rough.

In section the base of the sample shows a continuous dense iron oxide crust, coating the base of the slag and its

rounded inclusions (now secondary oxides). These inclusions resemble weathered iron droplets. The slag texture

has abundant primary wustite, which does not reach the base, followed by equant, somewhat skeletal olivine with

a complex leucite-rich interstitial material. The olivine is the most manganoan recorded in this sample, with inner

areas of Fa95 with 1% calcium and 5% manganese substitution and outer regions of Fa98 with 2% calcium and

5% manganese substitution.

Above this basal zone there are patches of dense wustite several millimetres across (presumably oxidised iron or

scale) bearing large, slightly tubular vesicles up to 400µm in diameter. Following the wustite, is elongate olivine

with a composition around Fa94 with 1% calcium and 4% manganese substitution. Leucite intergrown with

olivine and a leucite-wustite cotectic fill most of the space interstitial to the elongate olivine.

From this zone, stout elongate wustite dendrites extend upwards, forming the primary phase for 2mm of so (up to

a point about 7mm above the base). Between 7 and 8 mm above the base there are a few examples of wustite-

fayalite cotectic, but for the remainder of the section upwards the wustite becomes rapidly more delicate and

confined to the interstitial areas, suggesting that the slag is now in the field of primary fayalite. The proportion of

interstitial area increases upwards, but the sample does not reach the observed ‘glassy’ layer on the top of the

SHC.

Within this upper zone, the interstitial areas show a complex texture with both leucite (with the early stages of the

leucite intergrown with the margins of the olivine) and wustite dendrites (but only very small localised

development of a leucite-wustite cotectic), followed by what appears to be finely dendritic leucite in glass

(although a leucite-olivine cotectic may also be present, but the phases are too fine for individual analysis). The

main olivine shows inner regions of Fa93 with no calcium and up to 4% manganese substitution, passing to outer

regions of Fa99 with 1% calcium and 2% manganese substitution, which grade to margins of Fa100 with similar

substitution. The olivine intergrown with the leucite is similar, but with up to 2% calcium substitution.

Elemental variation in the slag composition is illustrated in Figure 2. This shows a peak iron concentration in the

dense wustite zone 1-5mm above the base. The basal region also shows the highest concentration of

manganese. The iron concentration drops rapidly from 3.5mm to 7mm above the base, with a corresponding rise

in silicon. The rate of change slows rapidly at around 7mm above the base, with the major elements fairly

constant from that point to the top (although there is still a minor gradient). In contrast the concentration of

potassium and calcium, both very low in the basal 5mm, show rapid upward increase between 5 and 6mm above

the base and thereafter a steady but low increase towards the top.


15


MHB2

In hand specimen this piece is one of two conjoining fragments of dense slag with a curved form, suggestive of

being the burr from an SHC.

In section, this sample has a relatively homogeneous microstructure, varying slightly in the proportion of the

mineral components, but with a similar microstructure throughout. As with MHB1, the lower part of the section is

much richer in wustite.

The primary phase is wustite in stout, rounded, small dendrites. As is usual the wustite shows considerable (5%

approximately) conversion to magnetite. The wustite is followed by complex, elongate, quench-textured olivine

with visible lengths in the section of approximately 1mm. The olivine extends into fine feathery dendritic

extensions pervading much of the interstitial space. Towards the top of the sample, the inner regions of the

olivine have compositions of approximately Fa92 with 1% calcium and 7% manganese substitution and grade to

external zones of composition Fa96 1with a similar degree of substitution, but in the lower, more wustite-rich

zones, the cores of the olivine may be as magnesian as Fa91 with 1% calcium and 9% manganese substitution.

MHB3

This sample comprises a section across a lobe of slag (about 15mm wide and 8mm high in the section, with a

central void), with an oxide crust and with a smaller lobe (approximately 4mm wide) attached to one side.

The main lobe has a surficial crust formed of an external radially platy or columnar layer, probably of hematite, up

to about 5 µm thick. Beneath this a 30-40µm thick layer of magnetite. On the internal side this layer appears to

overgrow and replace adjacent wustite dendrites, with both the outermost dendrites and the inner face of the

crust also showing the development of lamellar iscorite. The greatest depth below the surface to which any

iscorite was observed was about 110µm. The boundary between the two lobes is formed by the continuation of

the oxide crust of the main lobe, as a double layer of oxides with a string of central cavities, the whole being

approximately 25-40µm thick.

The internal slag texture is fairly homogeneous (Plate 2a), with primary wustite dendrites, followed by elongate

olivine, (very fine near the margins, but up to 1mm long internally). The olivine is mainly Fa97-98 with up to 1%

calcium substitution and 4% manganese substitution. The interstitial areas are of glass, with very fine blebs that

may be of iron sulphide.

MHB4

In hand specimen this specimen was apparently a tapped smelting slag of rather conventional appearance.

In section the piece proved to be very iron-rich, suggesting only a very low degree of iron extraction from the ore.

The texture was dominated by wustite, the distribution of which picked-out both flow lobes and zones that were

probably indicative of partially-reduced ore.

As with MHB3, the microstructural components were fairly simple, varying only in proportion. The primary phase

was always wustite, varying from blebby, almost polygonal textures, through (most commonly) rounded blebby

forms lacking clear dendritic structure, to more obvious rounded stout stubby dendrites and finally to delicate,

well-formed dendrites in the few areas where wustite was volumetrically subordinate to other phases.


16


The wustite was followed by elongate olivine, with an interstitial glass bearing abundant iron sulphide blebs. The

olivine was strongly manganoan, with typical compositions of Fa97-99 with up to 1% calcium substitution and

11% manganese substitution. The interstitial glass was noteworthy not only for its high proportion of sulphide

inclusions but also for its high sodium content – at 2 to 2.5 elemental wt%.

Interpretation

The elevated manganese contents of the iron working slags suggests that they inherited the element from the

smelting process – which would indicate that these are associated with bloom processing,

Sample MHB1 is a classic example of an SHC that appears to have formed a liquid puddle. The sequential EDS

analyses through the slag cake provide some good evidence for how the cake formed. The iron (or iron oxide)

lost from the work piece appears to have sunk through the puddle, accumulating and reacting at a point just

above its base (or actually reaching the base if the rounded voids with secondary iron oxides are weathered iron

droplets). The SHC therefore has a strong compositional gradient between about 3 and 8mm above its base,

above that level the slag is much more homogeneous. In contrast the inputs of silica, calcium and phosphorus

may have been from the top of the slag cake, resulting in particular with a steady upwards increase in calcium

and potassium through the upper part of the SHC. These two elements are likely to have been incorporated

through interaction with the fuel ash, either directly, or because of their fluxing action on the melting of the hearth

wall.

The implication that the iron component of the slag appears to have fallen through the puddle and reacted from

the bottom, would, perhaps, be more compatible with the origin of this SHC in conventional bloomsmithing than in

a hearth remelting technique.

Sample MHB2 appears to be from the burr region of an SHC and therefore does not show the same strong

succession as MHB1, and is instead much more homogeneous.

The smelting slags (MHB3 and 4) show chemical characteristics which are strongly suggestive of their derivation

from the smelting of a bog iron ore. This adds to the similar evidence provided by the early medieval site at South

Hook (some 8kms WSW; Crane & Murphy 2010). The evidence is not, however, quite unequivocal, as the barium

and phosphorus contents are not as elevated as they frequently are in bog iron ores. Although a bog iron ore is

considered the most likely source, the poorly-known, but locally manganiferous ochres of the Haverfordwest

district remain a slight alternative possibility.

The slags from Site 257 share many chemical characteristics with those placed in ‘Group 2’ at South Hook

(Young 2010a and 201b). There seems little doubt that they resulted from the exploitation of similar resources.

South Hook Group 2 slags were characterised, in particular, by high concentrations of zirconium (120-160ppm, or

500-950ppm in analyses recast on an iron-free basis) and also high contents of uranium (4-21ppm, or 25-90ppm

in analyses recast on an iron-free basis). The values for the Site 257 residues, when recast on an iron-free basis

are 598-724 ppm Zr and 18-144ppm for U. The REE profiles are similar, although not identical, with the Site 257

samples showing a more marked negative cerium anomaly and a tendency for the REE profile to remain inclined

through the HREE, whereas they are much flatter for most of the South Hook samples.

Young (2010b) suggested that the high Zr content of the South Hook Group 2 slags might suggest an origin

within, or close to, the outcrop of the Skomer Volcanic Group, a complex including several zirconium-rich bodies,


17


lying west of South Hook. The present study suggests that the relatively high-Zr input to the South Hook residues

might have come from elsewhere– potentially to the east of South Hook towards the Johnston area. Indeed,

recent analyses of residues from other sites, including Neath (Young 2014b), may suggest that such levels of Zr

may be more prevalent in South Wales than originally thought.

Conclusions

This evidence from Site 257 is for a primary iron production site, undertaking both bloomery iron smelting using a

slag-tapping furnace and bloom processing.

The chemical evidence suggests the exploitation of a bog iron resource (although in the lack of any analyses of

the Haverfordwest manganese-bearing ochres, there remains a slight element of doubt). The occurrence of bog

iron ores in this area is demonstrated by the find from Site 513 as well as by a small fragment from South Hook.

Neither of these samples provides a match for the predicted composition of the ores utilised at Site 257, but bog

iron compositions may vary rapidly, even within a very small area, in response to local groundwater conditions.

The chemical similarity with the South Hook Group 2 residues (Young 2010a, 2010b) is striking.


18


Table 1: Details of samples selected from MHA Site 257 further analysis. sample site context find weight notes

MHB1 257 257044 216 piece from bowl of SHC, concavo-convex, steep side with slightly haematised surface on interior, over 15mm

SHC with thick bladed fayalite, outer few mm finer, grading into rough outer surface; sample from below glassy(?) top MHB2 257 257044 90 dense but weathered burr from SHC?

MHB3 257 257044 hollow, tapslag like nub

MHB4 257 257044 tapslag fragment

Table 2: MHA Site 257: major element analyses of samples by XRF, expressed in oxide wt%. LOI = loss on ignition. Columns with tone give values recalculated to alternate valence state.

SiO2 Al2O3 Fe2O3 FeO Mn3O4 MnO MgO CaO Na2O K2O TiO2 P2O5 SO3 LOI Total

MHB1 20.24 2.50 72.92 65.63 1.07 1.00 0.63 0.23 0.33 1.60 0.21 0.55 0.09 -5.47 100.44 MHB2 12.50 1.91 79.21 71.29 2.23 2.07 0.70 0.58 0.31 1.48 0.21 0.59 0.08 -6.21 99.93 MHB3 10.46 1.34 85.55 76.99 1.55 1.44 0.30 0.02 0.15 0.54 0.09 0.69 0.19 -7.64 100.91 MHB4 6.34 1.71 86.66 78.00 3.69 3.43 0.31 0.06 0.08 0.32 0.14 0.46 0.12 -7.56 99.97

Table 3: MHA Site 257: trace elements analysed by ICP-MS, expressed in ppm.

Sc V Cr Co Ni Cu Zn Ga Rb Sr Y Zr Nb Mo Sn Cs Ba

MHB1 4.7 68.9 43.8 435.2 55.9 427.0 100.5 7.3 19.4 72.8 31.9 163.7 6.50 9.71 1.63 0.35 162.1 MHB2 3.7 40.2 45.8 555.4 369.7 59.0 37.3 6.3 14.7 89.6 38.0 133.4 4.37 5.10 0.35 0.28 160.0 MHB3 4.9 67.5 88.1 245.4 12.5 52.9 37.5 3.7 4.9 28.4 83.2 94.5 3.41 1.48 0.28 0.22 88.9 MHB4 4.5 80.6 55.0 479.9 6.3 485.7 125.1 7.4 4.6 33.1 93.9 93.9 2.64 5.13 1.43 0.37 145.7

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta Pb Th U

MHB1 11.79 15.63 3.22 13.12 3.28 0.89 3.99 0.64 4.27 0.84 2.63 0.43 2.81 0.44 3.62 0.75 3.60 3.16 4.98 MHB2 17.51 15.47 4.28 18.57 4.38 1.23 5.40 0.84 4.74 0.96 2.85 0.42 2.62 0.39 2.70 0.72 2.94 2.14 4.41 MHB3 21.66 21.89 6.76 31.35 8.79 2.36 10.25 1.59 9.52 2.01 6.24 0.99 6.79 1.11 1.84 2.53 2.42 1.47 10.51 MHB4 25.44 19.38 6.09 26.84 6.79 1.96 9.14 1.33 9.33 1.94 6.04 1.00 5.89 1.04 2.20 0.51 2.14 2.02 18.73

Site 257

Fig 2 Inset

Site 509

Site 271

Site 258

Site 272

BRECON BEACONS NATIONAL PARK

Gwendraeth Fach

Afon

Llyn

fi

A Rhy

Gwendraeth Fawr

East

ern

Cled

dau

R Lo

ugho

r

A Taf

R Tawel

A Tawe

Afron T

ywi

A Nyfer

A Cothi

A Rhondda Fach

A Rhondda Fawr

R Neath / A Nedd

A Cynin

A C

ywyn

Wes

ster

n Cl

edda

u

CARMARTHENSHIRE

SWANSEA

NEATH

PEMBROKESHIRE

AL PARKAL PARKPARA ARKPAL PARKACONS NATIOACONS NATIONABEAACCO S S OOATIONANNATNNAACEAB BBRECON BC BBBRECON

Gwendr

Gwendraeth FachFach

draeth

Afon

Lly

Afon

Llyn

fin

Lly

A

AA Rhy Rh

AA

endraet

Gwendraeth FawawrFa

East

ern

ster

n Cl

edda

uda

u

gR

Loug

hor

R Lo

ugho

r

A TafTaf

R Tawel

A Tawawe

aw

R Tawel

A Tawe

elA T

Afron T

ywi

Afron T

ywi

onAAffrfro

n TywTywi

A Nyfer

A Cothi

A C

A Rhondda Fach

ondda F

A R

awr

A Rhondda Fawr

A Rhondda

h / A Nedd

R Neath / A Nedd

R Neath / A Nedd

A Cynin

A Cyni

A C

ywyn

AC

ywyn

Cy

AC

ywWes

Wes

ster

n Cl

edda

udd

au

RRSHISSSNHENTTTTARAAAMRRARCACACC ESM NN RRMARR SS EEHHCARMARCARMARTHENSHIRE

ASSANAAAWWAWWSSW EEASWANS AS NNWSWANSSSWANSEA

ATHNEEEANNN HNEATH

ugug awawawug Tawu

CC

RSHIRSESEKKOOOOROROBRBEMP KKKK SHIRESOOBBMMP RR S EB HKPEMBROKESHIRE

MilfordHaven

Aberdulais

Felindre

Brecon

25km0

Site 257

N

0 1km

Reproduced from the 2005 Ordnance Survey Explorer map with the permission of Ordnance Survey on behalf of The Controller of Her Majesty's Stationery Office Crown copyright Cotswold Archaeology Ltd 100002109

c

CotswoldArchaeology

Cirencester 01285 771022

Milton Keynes 01908 218320

Andover 01264 326549

w www.cotswoldarchaeology.co.uk

e [email protected]

PROJECT TITLE

FIGURE TITLE

FIGURE NO.DATEREVISIONSCALE@A4

PROJECT NO.DRAWN BYAPPROVED BY

Milford Haven to Aberdulais pipeline

Felindre to Brecon pipeline

0-75m contour

75m contour

200m contour

400m contour

600m contour

Site location plan

South Wales Pipeline. Site 257, Land East ofRose Hill, Rosemarket, Pembrokeshire

9150DJBLM 1

09-10-2013001:25,000

0 15m

257007 257005

257023

257029

257049

257041

257033

257039

257035

257037

257043

257009

257021

257019

257018

257017

257003

257027

257025

257056

257013

257031

possibleenclosure

SMSM 942

093093 Site 257

N

0 100m1:5000

CotswoldArchaeology

PROJECT TITLE

FIGURE TITLE

FIGURE NO.DATEREVISIONSCALE@A3

PROJECT NO.DRAWN BYAPPROVED BY

94210

09286

SMSM

N

pipeline centreline

post-Roman gravel extraction pits

Roman

Plan showing archaeological features

South Wales Pipeline. Site 257, Land East ofRose Hill, Rosemarket, Pembrokeshire

09-10-2013001:200

9150DJBLM 2

Reproduced from the digital Ordnance Survey Explorer map with the permissionof Ordnance Survey on behalf of The Controller of Her Majesty's Stationery Office Crown copyright Cotswold Archaeology Ltd 100002109 c

Cirencester 01285 771022

Milton Keynes 01908 218320

Andover 01264 326549

w www.cotswoldarchaeology.co.uk

e [email protected]

South Wales Gas Pipeline Project Land East of Rose Hill · 2016-10-27 · South Wales Gas Pipeline Project Site 257 Land East of Rose Hill Rosemarket . Pembrokeshire Archaeological

Documents