Maes Coetmor Housing Development, Bethesda, Gwynedd ...

Archaeological Assessment

Maes Coetmor Housing Development,Bethesda, Gwynedd.August 2013

Project Code: A0019Report no. 0016

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Archaeological AssessmentAeon Archaeology17 Cecil StreetChesterCH3 5DP

Maes Coetmor Housing Development,Bethesda, Gwynedd.August 2013

Project Code: A0019Date: 05/08/2013Client: Carter JonasWri en by: Richard Cooke BA MA [email protected]

Report no. 0016

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Figure 01: Loca on of Monument points from the Gwynedd Historic Environment Record (HER). Scale 1:10,000 at A4.

Figure 02: Loca on of Listed Buildings and Scheduled Ancient Monuments. Scale 1:10,000 at A4.

Figure 03: Loca on of monument points as listed on the Na onal Monument Record. Scale 1:10,000 at A4.

Figure 04: Loca on of Historic Landscape Character Areas. Scale 1:10,000 at A4.

Figure 05: Map of the ‘Coytmor Demesne and part of the Coytmor Estate belonging to the Rt. Hon. Earl of Egmont’ Undated.

Figure 06: Plan of the Parish of Llanllechid 1822.

Figure 07: Tithe map for the parish of Llanllechid 1839.

Figure 08: First edi on 25” county series Ordnance Survey map of 1889.

Figure 09: Second edi on 25” county series Ordnance Survey map of 1900.

Figure 10: Third edi on 25” county series Ordnance Survey map of 1914.

Figure 11: Loca on of new archaeological sites iden fied during the desk-based assessment and loca on/direc on of photographs. Scale 1:2,500.

Figure 12: Archaeological deposit model. Scale 1:2,500 at A4.

Figures

PlatesPlate 01: Field bounary wall (feature 1), from the northeast. Scale 1.0m.

Plate 02: Field boundary wall (feature 2), from the northwest. Scale 1.0m.

Plate 03: Field boundary wall (feature 3), from the southwest. Scale 1.0m.

Plate 04: Field boundary wall (feature 4), from the southeast. Scale 1.0m.

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1.0 NON-TECHNICAL SUMMARY ....................................................................................... 1 2.0 INTRODUCTION, AIMS AND PROJECT DESIGN .................................................. 2 3.0 METHODS AND TECHNIQUES ................................................................................ 3

3.1 Archival research ............................................................................................................. 3 3.2 Site walkover ................................................................................................................... 3 3.3 Desk-based assessment report.......................................................................................... 3 3.4 Project archive ................................................................................................................. 4

4.0 ARCHAEOLOGICAL AND TOPOGRAPHICAL BACKGROUND ......................... 5 4.1 Topographic Description ................................................................................................. 5 4.2 Statutory and non-statutory designations ......................................................................... 5

4.2.1 Non-designated monument points from the Gwynedd Historic Environment Record (figure 1) ............................................................................................................................ 5 4.2.2 Listed Buildings (figure 2) ........................................................................................ 6 4.2.3 Scheduled Ancient Monuments (figure 2) ................................................................ 6 4.2.4 National Monuments Record (figure 3) .................................................................... 6 4.2.5 Historic Parks and Gardens ....................................................................................... 7 4.2.6 Historic Landscape Areas (figure 3) ......................................................................... 7 4.2.7 Events ........................................................................................................................ 7

5.0 THE HISTORICAL CONTEXT ......................................................................................... 9 5.1 Prehistoric and Roman Period ......................................................................................... 9 5.2 Early Medieval, Medieval and Post-Medieval Periods .................................................. 10 5.3 Aerial Photographs ........................................................................................................ 12

6.0 ASSESSMENT OF HISTORICAL ASSETS ................................................................... 13 6.1 Definitions ..................................................................................................................... 13

7.0 SITE GAZETTEER........................................................................................................... 16 8.0 IMPACT AND RECOMMENDATIONS ......................................................................... 22

8.1 Direct physical impact (see table 3)............................................................................... 22 8.2 Indirect physical and non-physical (visual) impact ....................................................... 22 8.3 Historic Landscapes................................................................................................. 22 8.4 Summary Results of the Geophysical Survey ......................................................... 22 8.5 Site Specific Recommendations .................................................................................... 22 8.6 General recommendations ............................................................................................. 23

9.0 SOURCES ......................................................................................................................... 24 APPENDIX 1: SCHEDULED AND NON-SCHEDULED SITES WITHIN 1.0KM ............ 26 APPENDIX 2: DEFINITIONS OF FURTHER ASSESSMENT AND MITIGATORY MEASURES ............................................................................................................................ 35 APPENDIX 3: GEOPHYSICAL REPORT BY STRATASCAN LTD . Error! Bookmark not defined.

1.0 Non Technical Summary

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1.0 NON-TECHNICAL SUMMARY Aeon Archaeology was commissioned by Carter Jonas to undertake an archaeological desk-based assessment of a proposed new housing estate as part of an outline planning application. The scheme is to include the construction of sixty-nine houses with access roads and landscaping, within a roughly triangular shaped piece of land spanning two grazing fields and measuring 2.4 hectares, within the town of Bethesda, Gwynedd. The archaeological desk-based assessment was undertaken in tandem with a geophysical survey carried out by Stratascan Ltd. The desk-based assessment ascertained that there are four sites of archaeological interest within the proposed development area, however these are all historic field boundaries considered to be of local importance. Of these one field boundary will require complete removal and one field boundary will require partial removal during the construction phase. The descriptions and photographs provided in this report are commensurate with a basic record level and as such no further assessment or mitigatory measures are proposed for these features. In addition the geophysical survey identified an area of possible archaeological pitting towards the centre of the north-western field. Due to the proximity of a plethora of archaeological sites within 1.0km of the development zone, the potential for the site to produce unknown buried archaeological remains is considered to be medium. Therefore, recommendations have been made for a limited programme of targeted archaeological trial trenching to assess the possible area of pitting identified in the survey, as well as to assess the potential of the south-eastern field which was not included in the geophysical survey due to an overgrowth of vegetation.

2.0 Introduction, Aims and Project Design

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2.0 INTRODUCTION, AIMS AND PROJECT DESIGN Aeon Archaeology was commissioned by Carter Jonas to undertake an archaeological desk-based assessment of a proposed new housing estate as part of an outline planning application (C13/0412/13/AM). The scheme is to include the construction of sixty-nine houses with access roads and landscaping, within a roughly triangular shaped piece of land spanning two grazing fields and measuring 2.4 hectares. The site is centred on NGR SH 61853 67241 and is bordered by Coetmor Road to the east and Coetmor New Road to the south, within the town of Bethesda, Gwynedd (figure 1). A mitigation brief (D1788) was prepared for this scheme by the Gwynedd Archaeological Planning Service (GAPS) which requested that a: ‘first phase of a staged programme of archaeological works be undertaken prior to planning consent, in accordance with guidelines set out in Planning Policy Wales 2012 and Welsh Office Circular 60/96 Planning and the Historic Environment: Archaeology. This phase will comprise an archaeological desk-based assessment and geophysical survey’. This archaeological desk-based assessment is for the proposed development area. As part of the archaeological desk-based assessment a 1.0km search area centred on the proposed development site was utilised for a search of the Gwynedd Historic Environment Record (HER). This provided a background historical narrative of the area and included source material from the Caernarfon Archives and Record Office, and the Bangor University archives. Information on Scheduled Ancient Monuments and Listed Buildings was obtained from Cadw. The following report conforms to the guidelines specified in Standard and Guidance for Archaeological Desk-based Assessment (Institute of Field Archaeologists, 1994, rev. 2007). The archaeological desk-based assessment considered the following:

(i) The history of the site; (ii) The significance of any remains in their context both regionally and nationally; (iii) The potential impact of the proposed development on known sites of archaeological

importance including their setting; (iv) The summary results of a programme of geophysical magnetometer survey; (v) The development of an archaeological deposit model to accurately depict the nature,

extent, and degree of survival of archaeological sites, structures, deposits, and landscapes within the study area.

The archaeological desk-based assessment was undertaken in four stages:

(i) Archival research (ii) Field visit/site walkover of all accessible areas (iii) Written report (iv) Project archive

In addition a geophysical magnetometer survey of the site was carried out by Stratascan Ltd the conclusions and recommendations of which have been incorporated into this report (section 8.4). A full copy of the geophysical report is reproduced in appendix III.

3.0 Methods and Techniques

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3.0 METHODS AND TECHNIQUES 3.1 Archival research The archaeological desk-based assessment involved the study of the following records:

• The regional Historic Environment Record (Gwynedd Archaeological Trust, Craig Beuno, Garth Road, Bangor, LL57 2RT) was examined for information concerning the study area. This included an examination of the core HER, and secondary information held within the record which included unpublished reports, the 1:2500 County Series Ordnance Survey maps, and the National Archaeological Record index cards and aerial photography.

• The National Monuments Record (NMR RCAHMW, National Monuments Record of

Wales, Plas Crug, Aberystwyth, SY23 1NJ) was checked for sites additional to the HER.

• Information about Listed Buildings and Scheduled Ancient Monuments from Cadw

were examined in the regional HER. The Register of Outstanding and Special Historic Landscapes and the Register of Parks and Gardens was checked, and also the location of World Heritage Sites.

• Secondary sources were examined, including the Inventories of the Royal

Commission on Ancient and Historical Monuments for Wales, and works held within the regional libraries.

• Evidence from aerial photographs was collated. Vertical and oblique collections held

by the NMR, CCW and Welsh Government were examination.

• Archive maps were consulted in the National Library of Wales at Aberystwyth, and at the Gwynedd archives. This included the relevant estate maps and tithe maps and information from Land Tax Assessments.

• Results from previous archaeological work within the area was also reviewed.

3.2 Site walkover The site walkover was carried out on 4th July 2013 by Richard Cooke BA MA MIfA, archaeological contractor and consultant at Aeon Archaeology. The weather conditions were ideal for the field search being both bright and clear. All archaeological sites and view points were photographed using a digital SLR (Canon 550D) set to maximum resolution. 3.3 Desk-based assessment report All features identified from the archival research and site walkover were assessed and allocated to categories of international, national, regional/county, local and none/unknown importance as listed in section 6.0. These are intended to place the archaeological feature within a geographical context of importance and thus help inform the most suitable level of mitigatory response. The criteria used for allocating features to categories of importance are based on existing statutory designations and, for non-designated assets, the Secretary of State's non-statutory criteria for Scheduling Ancient Monuments; these are set out in National Planning Policy Framework (NPPF) and Welsh Office Circular 60/96.

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3.4 Project archive A full archive including plans, photographs and written material was prepared. All plans, photographs and written descriptions were labelled and cross-referenced using Aeon Archaeology pro-formas. A draft copy of the report was sent to the client and upon written approval from them copies of the report will be sent to the regional HER (Gwynedd Archaeological Trust, Craig Beuno, Garth Road, Bangor, LL57 2RT), the Gwynedd Archaeological Planning Service, and the Royal Commission on the Ancient and Historic Monuments in Wales (RCAHMW). All notes, plans, and photographs arising from the desk-based assessment are stored at Aeon Archaeology under the project code A0019.

4.0 Archaeological and Topographical Background

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4.0 ARCHAEOLOGICAL AND TOPOGRAPHICAL BACKGROUND 4.1 Topographic Description The site comprises a plot of land totalling 2.4 hectares within the township of Bethesda, Gwynedd. Bethesda is a large village located to the southeast of Bangor, at the northern edge of the Snowdonia National Park Authority. The site consists of two fields of improved pasture forming a roughly triangular shape, bordered to the east by Coetmor Road, to the southwest by existing residential properties and to the northwest by similar improved pasture. Boundaries are defined by stone walling and post and wire fencing with some mature trees along boundaries and within the fields. The site slopes westwards towards the Afon Ogwen from approximately 160.0m to 140.0m Ordnance Datum. The site lies within the historic parish of Llanllechid. The site bedrock comprises the Llanberis Slates Formation. A sandstone sedimentary bedrock that formed approximately 518 to 545 million years ago in the Cambrian Period when the local environment was dominated by deep seas. Above this lies Devensian – Diamicton till, superficial deposits that formed up to 2 million years ago in the Quaternary Period when the local environment was dominated by Ice Age conditions (British Geological Survey). 4.2 Statutory and non-statutory designations 4.2.1 Non-designated monument points from the Gwynedd Historic Environment Record (figure 1) The Gwynedd Historic Environment Record (HER) maintains a register of non-designated archaeological sites represented as single point data or as polygons. These are identified through their Primary Reference Number (PRN). These include sites which are of archaeological/historical interest, artefact find spots, documentary evidence, and locations of past events such as archaeological projects. There are forty-three non-designated monument points within 1.0km of the boundary of the proposed development site (see appendix I) but only one monument is recorded within the site:

(i) Slate Quarry Coetmor (PRN: 20048). The site lies in close proximity to the following:

(i) Approximately 90.0m southeast of the post-medieval Coed Slate Quarry (PRN: 20047);

(ii) Approximately 180.0m east of the post-medieval Railway Underpass, No.

Tanysgafell (PRN: 5711);

(iii) Approximately 200.0m southeast of the post-medieval Site of 'Navy Oaks', Bangor Road (PRN: 5713);

(iv) Approximately 230.0m east of the post-medieval Quarry Scoops, north of Tanysgafell

(PRN: 5712);

(v) Approximately 230.0m southeast of the post-medieval Copper Mine, Coed y Dinas (PRN: 29617).

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4.2.2 Listed Buildings (figure 2) The Secretary of State for Culture, Media and Sport holds a List of Buildings of Special Architectural or Historic Interest, considered to be of national importance. Compiled under the Planning (Listed Buildings and Conservation Areas) Act 1990, the List includes structures from boundary walls and telephone boxes to cathedrals. Listing gives statutory protection and restrictions apply. Consent may be required for works to, or that affect the setting of, a Listed Building and the Local Planning Authority conservation officer should be consulted if in doubt. There are forty Listed Buildings within 1.0km of the proposed development area (see appendix I) but none lie within the site boundary. The site lies in close proximity to the following:

(i) Approximately 190.0m north of the grade II Listed Building of Capel Bethania (LB

ref: 18384); (ii) Approximately 190.0m south of the grade II Listed Building of Coetmor Farmhouse

(LB ref: 18397);

(iii) Approximately 210.0m south of the grade II Listed Building of Barn at Coetmor Farm (LB ref: 18398);

(iv) Approximately 230.0m south of the grade II Listed Building of Outbuildings in farm-

court at Coetmor Farm (LB ref: 18399). 4.2.3 Scheduled Ancient Monuments (figure 2)

Scheduled monuments are those considered to be monuments of national importance. The Ancient Monuments and Archaeological Areas Act 1979 supports a formal system of Scheduled Monument Consent (SMC) for any work to a designated monument. Any works within a Scheduled area will require SMC; this includes non-invasive techniques such as geophysics or field-walking. There is one Scheduled Ancient Monument within 1.0km of the proposed development area (see appendix I) but none lie within the site boundary. The site lies in close proximity to the following:

(i) Approximately 800.0m northeast of the post-medieval Slate Gwaliau at Felin Fawr,

Penrhyn Scheduled Ancient Monument (SAM: CN297). 4.2.4 National Monuments Record (figure 3) The Royal Commission on the Ancient and Historic Monuments in Wales (RCAHMW) maintains the National Monuments Record (NMR) for Wales. This is a register of non-designated archaeological sites represented as single point data or as polygons. These are identified through their National Primary Reference Number (NPRN) and include sites which are of archaeological/historical interest, artefact find spots, documentary evidence, and locations of past events such as archaeological projects that are not statutorily protected. There are forty-five non-designated monument points within 1.0km of the boundary of the proposed development area (see appendix I) but none lie within the site boundary. The site lies in close proximity to the following:

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(i) Approximately 70.0m west of the post-medieval Cloverly Lodge Garden Craigside (NPRN: 86,338);

(ii) Approximately 100.0m southwest of the post medieval Coetmore Hall Garden

(NPRN: 86,347)

(iii) Approximately 180.0m northwest of the post-medieval Bethania Welsh independent Chapel, Penrhyn Terrace, Bangor Road, Bethesda (NPRN: 6733).

4.2.5 Historic Parks and Gardens Cadw holds a Register of Historic Parks and Gardens of Special Historic Interest. These Registered landscapes are graded I, II* or II, and include private gardens, public parks and other green spaces. They are valued for their design, diversity and historical importance. Inclusion on the Register brings no additional statutory controls, but there is a presumption in favour of conservation of the designated site. Local authorities are required to consult Cadw on applications affecting sites Registered as grade I or II* and the Garden History Society on sites of all grades. There are no historic parks and gardens within the site boundary or within 1.0km of the proposed development area. 4.2.6 Historic Landscape Areas (figure 4) Cadw, National Resource Wales (formerly the Countryside Council for Wales), and the International Council of Monuments and Sites (ICOMOS UK) compiled the two volume Register of Landscapes of Historic Interest in Wales. This includes 58 landscapes of outstanding or special historic interest, which are considered to be the best examples of different types of historic landscapes in Wales. The Register provides information to decision makers and landscape managers, to help ensure that the historic character of the landscape is sustained, and that where change is contemplated, it is well-informed. The proposed development site lies within the following Historic Landscape Area (HLA):

(i) The Ogwen Valley Landscape of Outstanding Historic Interest (HLW (Gw) 10). Historic Landscape Characterisation takes a closer look at the historic landscape by showing the processes that have shaped the landscape over centuries of human activity, contributing to its present character. Detailed characterisation studies have been compiled by the four Welsh Archaeological Trusts for all 58 areas on the Register. They are used by local government and developers to help assess the impact of development proposals on the historic landscape. The proposed development area lies within the following Historic Landscape Character Areas (HLCAs):

(i) Partially within the fieldscape around Llanllechid HLCA (38); (ii) Partially within the Bethesda and Llanllechid HLCA (12).

4.2.7 Events There has not been any past project work undertaken by Aeon Archaeology or any other archaeological contractor within the proposed development site. However, in the 1990s two archaeological desk-based assessments were undertaken close to the application site, in

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connection with a new water main (Gwynedd Archaeological Trust reports 69 and 125) and a proposed bypass (GAT report 59). However, while these did result in new information, fieldwork was limited. Both projects appear to have skirted the site and the reports contain no specific detail relevant to it.

11688

15838

15877

20047

20048

20053

20058

20059

20812

20821

20822

21185

21947

261

29617

30446

31746

36224

3674

5706

57075708

5709

5710

57115712

5713

5714

57155716

5717

5745

5746

5747

5891

17819 Rom

an Road

Aeon ArchaeologyRichard Cooke BA MA MIfA

17 Cecil Street, Boughton, Chester. Cheshire CH3 5DPTel: 07866925393

www.aeonarchaeology.co.uk

Figure 1: Loca on of Monument points from the GwyneddHistoric Environment Record (HER). Scale 1:10,000 at A4. (Numbers refer to HER Primary Reference Number (PRN), see report appendix I; proposed development site outlined in blue)

Contains Ordnance Survey data © Crown copyright and database right 2013

CN297

4156

41554154

23474

23473

2340123400

3663 18400

1839918398

18397

1839118392

18390

1839318386

18394

18395

18388

183894145

18415

18414

18387

18385

18417

18416

18409

41594157

4153

18383

18384

22975

23369

23414

23417

4158




Figure 2: Loca on of Listed Buildings (purple crosses) and Scheduled Ancient Monuments (red polygons). Scale 1:10,000 at A4. (Numbers refer to designa on ID, see report appendix I; proposed development site outlined in blue)


570

24676

415255

308412

406153308413

416939

406185

6735

11952

26689

404774

11953402775

26412415226

411155

43664

6751

309196

300987

6733

6756

6753

86310

86338

86348

11947

6747

6742

6739

6737

6749

86315

23786

86347

409723

409724

409725

411381

417671




Figure 3: Loca on of monuments (blue triangles) as listed on the Na onal Monument Record (NMR). Scale 1:10,000 at A4. (Numbers refer to Na onal Primary Reference Number (NPRN), see report appendix I; proposed development site outlined in blue)


15838

15863

15877

15862

15825

15861

15858




Figure 4: Loca on of Historic Landscape Character Areas (HLCAs). Scale 1:10,000 at A4. (Numbers refer to HLCA ID, see report appendix I; proposed development site outlined in blue)


5.0 The Historical Context

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5.0 THE HISTORICAL CONTEXT The following sections describe the known archaeological record within the general area of the proposed development. Sites are identified by their Primary Reference Number (PRN) which is the number by which they are identified in the Gwynedd Historic Environment Record (HER), or by their Scheduled Ancient Monument reference, or Listed Building reference numbers if applicable. The intention of this section is to provide a historic and archaeological context to the site. This aids in establishing the relative importance of an archaeological feature within its landscape, as well as assessing the potential for unknown buried archaeological remains on the proposed development site. The beginning and end of certain periods is a contentious issue. In the Gwynedd Historic Environment Record (HER) the following dates are used. This is a standard convention across all of the Welsh HERs.

Table 1. Historic periods Palaeolithic (prehistoric) 500,000 BC – 10,001 BC Mesolithic (prehistoric) 10,000 BC – 4,001 BC Neolithic (prehistoric) 4,000 BC – 2,351 BC Bronze Age (prehistoric) 2,350 BC – 801 BC Iron Age (prehistoric) 800 BC – 47 AD Romano-British 48 AD – 409 AD Post-Roman (Early Medieval) 410 AD – 1065 AD Medieval 1066 AD – 1539 AD Post-Medieval 1540 AD – 1900 AD Modern 1901 AD – 2050 AD

5.1 Prehistoric and Roman Period The site is located within the Ogwen Valley Registered Landscape of Outstanding Historic Interest, designated primarily for the range and quality of its prehistoric and industrial archaeology. There are no known prehistoric sites within close proximity to the proposed development site however in the wider landscape prehistoric settlements (hillforts and hut circles) exist mainly on the uplands that have been unaffected by later activity, but also at similar locations to the application site. Away to the north and northeast of the site the upland slopes contain several prehistoric Scheduled Ancient Monuments including the Settlements and Enclosures on the South and East Sides of Moel Faban (SAM: CN210), the Early Fields and Dwellings East of Llanllechid (SAM: CN121), the Fortified Hut Settlement above Rachub (SAM: CN211), the Moel Faban cairn cemetery (SAM: CN359), the Pen Dinas Camp (SAM: CN120), and the Coed Uchaf Hut Group (SAM: CN176). The latter of these Scheduled Ancient Monuments consists of an enclosed hut group, on level ground, consisting of an oval enclosure surrounded by a bank of earth and stones 2.5m thick, faced on both sides with orthostats. The entrance to the enclosure lies to the southeast but is blocked by a later wall of piled boulders thrown across its outer end. Within the enclosure are the remains of three buildings, one rectangular and two circular chambers, situated in the corner of an uncleared field. The surrounding wall, which has been extensively robbed, is irregular in form, presenting a rather zigzag appearance. It is not unlikely that it was intended more as a protection from wolves, or as a plan to keep the cattle within the area, than as a fortification. The road which led to these remains appears to have taken a northerly course, judging from a slight difference in the level of the ground in that direction, in which case it

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may have connected this group with other similar ones on the side of the mountain. In hut 2 was found a large hearthstone, slag, unburnt peat, charcoal and the dust of burnt peat. There were no signs of a fireplace in hut 3. In the rectangular building finds included a whetstone, charcoal, peat ashes and a quantity of rounded broken stones possibly used for cooking food and boiling water. To the south and west of the hut group is a series of terraced fields which are strongly developed and lined by rough walls of piled stones. Three of these abut against the enclosure wall at various points and the hut group and fields are most likely contemporary (HER). Approximately 850.0m to the northwest of the proposed development site an archaeological desk-based assessment carried out in 1993 by the Gwynedd Archaeological Trust (GAT report 61) identified, within a heavily wooded area with thick low level vegetation, an area of strewn stone. The stone was concentrated within several circular areas and their size and shape were suggestive of prehistoric or Romano-British hut circles (PRN: 5745). The report went on to identify a second potential prehistoric hut circle site further to the north and approximately 1.0km from the proposed development site (PRN: 5744). The Roman period is not as intensely represented as the prehistoric period within the nearby landscape. However evidence of the Roman period can be seen approximately 880.0m to the east of the proposed development site at the Pen y Gaer Hillfort (PRN: 261). This site consists of a roughly oval defended enclosure, occupying the summit of a small hill. The rampart is overlaid by modern stone walls, and sheepfolds occupy part of the interior, but enough remains to show that the bank was of loose stones faced on both sides with orthostats and boulders laid lengthwise. The area surrounding the hillfort contains a series of linear arrangements of stones, possibly the remains of old field boundaries associated with the hillfort. These appear to cross the present course of the small stream running along the base of the slope of the hillfort (GAT report 61). In closer proximity to the proposed development site the proposed route of the Roman road from Caer Llugwy to Bangor (PRN: 17819) runs from north to south, approximately 550.0m to the west of the site. A report from Tim Strickland of Gifford and Partners shows through geological analysis that a slate used in the roofing of legionary barracks in Chester (Princess Street, 1981/2) had come from within a mile of Bethesda. This perhaps adds credence to the idea of a Roman road running down the Ogwen valley at this location (HER). 5.2 Early Medieval, Medieval and Post-Medieval Periods The Early Medieval period is poorly represented within this part of northwest Wales and there are no known archaeological sites or finds within 1.0km of the proposed development site. By the 12th and 13th centuries the kingdom of Gwynedd was divided into administrative commotes, administered through a network of local centres governed by a royal court or Llys. The township of a commote associated with a llys was known as the maerdref, in which the Prince’s agent would reside. The component parts of a llys included the royal hall and other buildings associated with the residence, as well as the royal demesne worked by bond tenants, and the settlements of these tenants which constituted small hamlets. The llys and royal lands became the property of the English King upon the conclusion of the conquest of Wales. There are only two known Medieval sites within 1.0km of the proposed development site. Both of these are hut platforms (PRNs: 299 and 298) and are located 830.0m and 950.0m to the north of the site respectively. The proposed development area is depicted on the undated map of the Coytmor Demesne and part of the Coytmor Estate belonging to the Rt. Hon. Earl of Egmont (figure 5). The exact location of the proposed development site is difficult to place but appears to partially occupy an area that was four enclosed grazing fields, to the immediate southwest of Coetmor Hall. The landscape is depicted rather differently to how it exists today as there had not been any

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urban sprawl from nearby Bethesda, and the Coetmor Road and Coetmor New Road had not been constructed. As such the map field boundaries do not entirely correspond with the modern layout. The development area and the immediate surrounding land was owned at this time by the Earl of Egmont who, if the map is of early to mid 19th century, would have been George Perceval the 6th Earl of Egmont who lived from 1794-1874. George Perceval was the third but eldest surviving son of Charles Perceval, 2nd Baron Arden, eldest son of John Perceval, 2nd Earl of Egmont, by his second wife Catherine, Baroness Arden. Prime Minister Spencer Perceval was his uncle. He was commissioned into the Royal Navy in 1805 and fought in the H. M. S. Orion in the Battle of Trafalgar the same year, aged eleven. During the Bombardment of Algiers in 1816 he commanded the H. M. S. Infernal. He was promoted to Rear-Admiral in 1851, to Vice-Admiral in 1857 and to Admiral in 1863. Egmont was returned to Parliament as one of two representatives for Surrey West in 1837, a seat he held until 1840. The latter year he succeeded his father in the barony of Arden and entered the House of Lords. The following year he also succeeded his first cousin once removed as sixth Earl of Egmont (Dodd, C.R.). The proposed development area is again depicted on the 1822 Penrhyn Plan of the Parish of Llanllechid (figure 6) but unfortunately not in any real detail. The field boundaries are not shown and aside from Coetmor Hall, which is depicted as four buildings enclosed by a perimeter boundary, the agricultural land is shown as one large blank area. Of note however is the depiction of a trackway running from northeast to southwest at the southern end of the main approach to Coetmor Hall. This trackway does not correspond with any known track and is not depicted on the later parish tithe map of 1839 (figure 7). It does however appear to be located to the south of the proposed development area under what are now the rear gardens of the houses fronting on to Bangor Road. The proposed development area is depicted on the later 1839 Tithe Map for the Parish of Llanllechid (figure 7). This map again depicts the area in very little detail as the field boundaries are not shown, and the depicted enclosures represent land ownership boundaries rather than individual fields. The map does however show Coetmor Hall towards the north of the development area and the accompanying tithe apportionment details that the landowner is still the Earl of Egmont.

Table 2. Apportionment to the 1839 Tithe Map for the Parish of Llanllechid Field Number

Field Name Landowner Occupier A/R/P

101 Coetmor Earl of Egmont William Williams and Partners

166/0/3

The proposed development site is depicted in detail on the first, second and third edition county series 25” Ordnance Survey maps of 1889, 1900, and 1914 respectively (figures 8, 9, and 10). The first edition map depicts the development area as occupying two fields as it does today, however the south-eastern field is shown as being smaller than it currently is, and the development boundary extends southeast outside of the field boundary into a belt of woodland. By the production of the second edition map in 1900 the south-eastern field had been enlarged to encompass part of the belt of trees and the site is shown as being of the same layout as how it currently exists. In conjunction with this the Coetmor New Road is depicted on the 1900 map and it can be surmised that the south-eastern field boundary was extended to incorporate the land to the west of the road into the enclosed field. All three edition maps depict an old quarry to the immediate west of the site beneath what is now a belt of trees. A second larger quarry is depicted to the immediate southeast of the site

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which is labelled quarry on the first edition map but old quarry on the second and third editions. The Gwynedd HER depicts the monument point Slate Quarry Coetmor (PRN: 20048) as being within the south-eastern field of the proposed development site, however this is clearly a mistake and actually refers to the larger slate quarry depicted to the southeast of the site. The first three edition Ordnance Survey maps do not depict any structures or features of interest, aside from the first edition field boundary, within the proposed development area. The surrounding landscape on the maps is shown rather more similarly to how it exists today as by the production of the first edition map Coetmor Cottage had been built to the northeast and a small row of houses had been constructed to the southwest fronting on to Bangor Road. 5.3 Aerial Photographs As part of the archaeological desk-based assessment the RCAHMW was visited to examine available historic aerial photographs of the proposed development area. The 1940s RAF photographs were found to not cover this part of Bethesda and the earliest photograph available was taken by the Ordnance Survey in 1984. This showed the development area in detail but no archaeological sites or features could be identified within or in close proximity to the development area. Modern Ordnance Survey photographs dating to 2009 and 2012 were also examined but no additional sites noted.




Figure 5: Map of the ‘Coytmor Demesne and part of the Coytmor Estate belonging to the Rt. Hon. Earl of Egmont’ Undated.(approximate loca on of proposed development site outlined in blue)




Figure 6: Plan of the Parish of Llanllechid 1822. (approximate loca on of proposed development site outlined in blue)




Figure 7: Tithe map for the parish of Llanllechid 1839. (approximate loca on of proposed development site outlined in blue)




Figure 8: First edi on 25” county series Ordnance Survey map of 1889. (approximate loca on of proposed development site outlined in blue)




Figure 9: Second edi on 25” county series Ordnance Survey map of 1900. (approximate loca on of proposed development site outlined in blue)




Figure 10: Third edi on 25” county series Ordnance Survey map of 1914. (approximate loca on of proposed development site outlined in blue)

6.0 Assessment of Historical Assets

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6.0 ASSESSMENT OF HISTORICAL ASSETS 6.1 Definitions Definitions of importance, impact, and significance of effect as used in the gazetteer (section 6.2) are listed below. Definitions of assessment and mitigation techniques as used in the gazetteer are listed in appendix II. 1. Definition of Categories of importance The following categories were used to define the importance of the archaeological resource. Significance Description International (Very High)

Archaeological sites or monuments of international importance, including World Heritage Sites. Structures and buildings inscribed as of universal importance as World Heritage Sites. Other buildings or structures of recognised international importance.

National (High)

Ancient monuments scheduled under the Ancient Monuments and Archaeological Areas Act 1979, or archaeological sites and remains of comparable quality, assessed with reference to the Secretary of State’s non-statutory criteria. Listed Buildings. Undesignated structures of national importance.

Regional/ County (Medium)

Conservation Areas Archaeological sites and remains which, while not of national importance, score well against most of the Secretary of State’s criteria.

Local (Low)

Archaeological sites that score less well against the Secretary of State’s criteria. Historic buildings on a 'local list'.

Negligible/None Areas in which investigative techniques have produced no or only minimal evidence for archaeological remains, or where previous large-scale disturbance or removal of deposits can be demonstrated.

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2. Definition of Impact The direct impact of the proposed development on each site was estimated. The impact is defined as follows: Magnitude Direct Impacts Indirect Impacts High Adverse Complete removal of an

archaeological site. Complete destruction of a designated building or structure.

Radical transformation of the setting of an archaeological monument. A fundamental change in the setting of a building.

Medium Adverse Removal of a major part of an archaeological site and loss of research potential. Extensive alteration (but not demolition) of a historic building or feature, resulting in an appreciable adverse change.

Partial transformation of the setting of an archaeological site (e.g. the introduction of significant noise or vibration levels to an archaeological monument leading to changes to amenity use, accessibility or appreciation of an archaeological site). Partial adverse transformation of the setting of a designated building.

Low Adverse Removal of an archaeological site where a minor part of its total area is removed but the site retains a significant future research potential. Change to a historic building or feature resulting in a small change in the resource and its historical context and setting.

Minor change to the setting of an archaeological monument or historic building.

Negligible/ Neutral

No impact from changes in use, amenity or access. No change in the ability to understand and appreciate the resource and its historical context and setting.

No perceptible change in the setting of a building or feature.

Low Beneficial Land use change resulting in improved conditions for the protection of archaeological remains or understanding/ appreciation of a historic building or place

Decrease in visual or noise intrusion on the setting of a building, archaeological site or monument. Improvement of the wider landscape setting of a building, archaeological site or monument.

Medium Beneficial

Land use change resulting in improved conditions for the protection of archaeological remains, or understanding/ appreciation of a historic building or place, including through interpretation measures (heritage trails, etc). Removal of harmful alterations to better reveal the significance of a building or structure, with no loss of significant fabric.

Significant reduction or removal of visual or noise intrusion on the setting of a building, archaeological site or monument; and Improvement of the wider landscape setting of a building, archaeological site or monument Improvement of the cultural heritage amenity, access or use of a building, archaeological site or monument.

High Beneficial

Arrest of physical damage or decay to a building or structure;

Exceptional enhancement of a building or archaeological site, its cultural heritage amenity and access or use

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3. The significance of effect The significance of effect is derived from the importance of the resource and the magnitude of the impact upon it. Very large - A serious impact on a site of international or national importance with little or no scope for mitigation. These effects represent key factors in the decision making process. Large - Lesser impacts on sites of national importance and serious impacts on sites of regional importance, with some scope for mitigation. These factors should be seen as being very important considerations in the decision making process. Moderate - Moderate or minor impacts on sites of regional importance and minor to major impacts on sites of local or minor importance. A range of mitigatory measures should be available. Slight - Negligible impacts on sites of regional, local or minor importance and minor and moderate impacts on minor or damaged sites. A range of basic mitigatory measures should be available. Neutral - No perceptible effect or change to sites of all categories. The significance of effect will be determined using the table below, a basic matrix combining archaeological value and magnitude of impact. Determination of Significance of Effect

Arc

haeo

logi

cal V

alue

International Slight Moderate or Large Large or Very Large

Very Large

National Slight Moderate or Slight Moderate or Large

Large or Very Large

Regional Neutral or Slight Slight Moderate Moderate or Large

Local Neutral or Slight Neutral or Slight Slight Moderate or Slight

Negligible Neutral Neutral or Slight Neutral or Slight

Slight

None Low Medium High

Magnitude of impact

7.0 Site Gazetteer

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7.0 SITE GAZETTEER The field walkover discovered four sites of archaeological and historic interest within, or in close proximity to the proposed development corridor, as listed below. In accordance with Paragraph 128 of the National Planning Policy Framework and Welsh Office Circular 60/96 each heritage asset has been assigned a level of importance ranked from International through to National, Regional/County, Local, and None. If it is not possible to assess the importance of the site from the visible remains, then it is ranked Unknown with the suspected importance level placed in brackets if possible. Identified sites were also assigned a level of impact ranked from High through to Medium, and Low. Levels of impact can be considered as both adverse or beneficial, and can be direct (physically impacting upon a site) or indirect (visually or indirectly physically impacting upon a site). The significance of effect is determined from the importance level of the resource and the magnitude of the impact upon it. Where it is expected that a site will be impacted upon by the proposed works then mitigation/assessment recommendations are provided. All archaeological/historical sites identified are depicted on figure.11 along with the location and direction of photographs.

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1. Field boundary wall

PRN: 38058 Figure: 11

Plate: 1

NGR: SH 61900 67125 – SH 61782 67276

Period: Post-Medieval

Description A dry-stone field boundary wall measuring approximately 1.2m in height runs from southeast to northwest and marks the south-western limit of the proposed development site. It is of single-skin construction of medium sized sub-angular stones with a single stock proof course. The wall is reinforced by a modern wood post and wire fence. The boundary is first depicted on the first edition 25” county series Ordnance Survey map of 1889 (figure 8) but appears to also be shown on the undated Earl of Egmont Estate map (figure 5) which is most probably of early 19th century date. The boundary wall will be retained as part of the development and as such will not be impacted upon. Category of importance: Local Level of impact: None Significance of effect: Neutral Recommendations for further assessment: None Recommendations for further mitigatory measures: Retain in-situ

Plate 01: Field bounary wall (feature 1), from the northeast. Scale 1.0m.

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Plate: 2

NGR: SH 61781 67276 – SH 61919 67354


Description A dry-stone field boundary wall measuring approximately 1.2m in height runs from northeast to southwest and divides the proposed development site into two grazing fields. It is of single-skin construction of medium sized sub-angular and sub-rounded stones. The wall is reinforced in places by a modern wood post and wire fence and has suffered from collapse at various points. The boundary is first depicted on the first edition 25” county series Ordnance Survey map of 1889 (figure 8) but appears to also be shown on the undated Earl of Egmont Estate map (figure 5) which is most probably of early 19th century date. The boundary wall will be required to be removed as part of the development and as such it is recommended that a basic record be taken of the wall prior to demolition. However, the description, plans and photographs provided in this report should be seen as being commensurate with a basic record level and as such no further assessment or mitigatory measures are proposed. Category of importance: Local Level of impact: High adverse direct physical Significance of effect: Slight adverse Recommendations for further assessment: None Recommendations for further mitigatory measures: None – basic record included as part of this assessment

Plate 02: Field boundary wall (feature 2), from the northwest. Scale 1.0m.

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Plate: 3

NGR: SH 61900 67125 – 61918 67355

Period: Post Medieval

Description A stone field boundary wall measuring approximately 1.0m in height runs from north to south and marks the eastern limit of the proposed development area. It is of single-skin construction of medium sized sub-angular stones bonded by mortar with a single stock proof course. The boundary is first depicted on the first edition 25” county series Ordnance Survey map of 1889 (figure 8) and is most likely contemporary with the construction of Coetmor Road sometime between 1839 (figure 7) and 1889 (figure 8). The boundary wall will be retained as part of the development but will require to be breached at the south-eastern end in order to provide road access to Coetmor New Road. Category of importance: Local Level of impact: Low adverse physical Significance of effect: Neutral/slight adverse Recommendations for further assessment: None Recommendations for further mitigatory measures: Retain in-situ

Plate 03: Field boundary wall (feature 3), from the southwest. Scale 1.0m.

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Plate: 4

NGR: SH 61782 67276 - 61918 67355


Description A dry-stone field boundary wall measuring approximately 1.2m in height runs from northeast to southwest and marks the northern limit of the proposed development site. It is of single-skin construction of medium sized sub-angular and sub-rounded stones. The boundary is first depicted on the first edition 25” county series Ordnance Survey map of 1889 (figure 8) but appears to also be shown on the undated Earl of Egmont Estate map (figure 5) which is most probably of early 19th century date. The boundary wall will be retained as part of the proposed development and as such will not be impacted upon. Category of importance: Local Level of impact: None Significance of effect: Neutral Recommendations for further assessment: None Recommendations for further mitigatory measures: Retain in-situ

Plate 04: Field boundary wall (feature 4), from the southeast. Scale 1.0m.

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Table 3: Summary of archaeological features

Number Name Importance Impact Significance of effect

Further Assessment

Mitigation Recommendations

1 Field boundary wall Local None Neutral None Retain in-situ 2 Field boundary wall Local High adverse physical Slight adverse None None – basic record

included as part of this assessment

3 Field boundary wall Local Low adverse physical Neutral/slight adverse

None Retain in-situ

4 Field boundary wall Local None Neutral None Retain in-situ

Hafod y Coed

Derlwyn

Gorpwys

fa

7

Coedmadog

BrynOnn

en

Villa

Path(um

)

Hengoed

Pat

h( u

m)

Ex

Ogwen Villa

Bodarfr

yn

Bonlondeb

Meifod

Ystradawel

Playground

Maesy Garr

eg

13

COETM

ORNEW

ROAD

1

6

Maes Coetmor

Glasgo

ed

Ffos Coetmor

MinOgw

en

Gwynfa

Tel

Rhosla

n

Dolwern

Assessment Area

1 2

34

12

3

4




Figure 11: Loca on of new archaeological sites iden fied during the desk-based assessment (numbered diamonds) and loca on/direc on of photographs (numbered arrows). Scale 1:2,500.

8.0 Impact and Recommendations

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8.0 IMPACT AND RECOMMENDATIONS 8.1 Direct physical impact (see table 3) Construction phase The proposed development scheme is expected to have a low adverse direct physical impact upon one site (feature 3) of archaeological significance and a high adverse direct physical impact upon one site (feature 2) of archaeological significance. Both of these sites are field boundary walls of local significance. Completion phase The proposed development scheme is not expected to have any further direct physical impact upon any archaeological features upon completion. 8.2 Indirect physical and non-physical (visual) impact Construction phase The proposed development scheme is not expected to have any indirect physical and non-physical impacts upon any archaeological features during the construction phase. Completion phase The proposed development scheme is not expected to have any indirect physical and non-physical impacts upon any archaeological features upon completion. 8.3 Historic Landscapes The south-eastern field of the proposed development site lies within the fieldscape around Llanllechid Historic Landscape Character Area (38) and the north-western field lies within the Bethesda and Llanllechid Historic Landscape Character Area (12) within the Ogwen Valley Landscape of Outstanding Historic Interest (HLW (Gw) 10). If the proposed development is permitted then the north-western field would be amalgamated into the Bethesda and Llanllechid Historic Landscape Character Area (12) resulting in a loss of 0.3% of the fieldscape around Llanllechid Historic Landscape Character Area (38). 8.4 Summary Results of the Geophysical Survey The survey at Bethesda did not identify any anomalies of probable archaeological origin. An area of possible pitting of archaeological origin as well as areas of possible quarrying were identified towards the middle of the north-western field; however these anomalies could also have a geological origin. Much of the rest of the site is covered by magnetic variation, likely of geological origin. The remaining anomalies are of modern origin, relating to an underground service and modern ferrous objects. A large part of the perimeter of the south-eastern field could not be surveyed due to bracken vegetation. 8.5 Site Specific Recommendations It is expected that the proposed development will impact physically upon two sites of local archaeological significance (features 2 and 3), both of which are historic field boundaries. The descriptions and photographs supplied within this report should be seen as being commensurate with a basic record level and as such no further assessment or mitigatory measures are proposed for any of the sites identified.

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8.6 General recommendations Due to the proximity of a range of archaeological sites of all periods, in particular of the prehistoric period, coupled with the identification of possible archaeological pits towards the centre of the north-western field during the geophysical survey, the potential for unknown buried archaeological remains on the site is considered to be medium (figure 12). As such it is recommended that a limited programme of targeted trial trenching is undertaken to assess the possible pits identified in the geophysical survey as well as to assess the potential of the south-eastern field.

Hafod y Coed

Derlwyn

Gorpwys

fa

7

Coedmadog

BrynOnn

en

Villa

Path(um

)

Hengoed

Pat

h( u

m)

Ex

Ogwen Villa

Bodarfr

yn

Bonlondeb

Meifod

Ystradawel

Playground

Maesy Garr

eg

13

COETM

ORNEW

ROAD

1

6

Maes Coetmor

Glasgo

ed

Ffos Coetmor

MinOgw

en

Gwynfa

Tel

Rhosla

n

Dolwern

Maes Coeetmore

Assessment Area

Utility pipe

Historic quarrying

Historic quarrying

Possible pitting




Figure 12: Archaeological deposit model (areas of archaeological poten al shown in red; areas of unknown archaeological poten alshown in yellow; areas of no archaeological poten al shown in green). Scale 1:2,500.

9.0 Sources

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9.0 SOURCES OS Maps 1st edition 25 inch Ordnance Survey Map of 1889. 2nd edition 25 inch Ordnance Survey Map of 1900. 3rd edition 25 inch Ordnance Survey Map of 1914. OS 1:10 000 Series sheet SH 66NE, SH 66SE, SH 66SW, and SH 66NW. OS Landmark data as supplied by Promap Ltd. Aerial Photographs RAF CPE/UK/2615. Frame 3486, 26th April 1948. 541/178. Frames 3207 and 3208, 8th October 1948. OS Aerial Photographs 84-108. Frames 70 and 71, 1984. 94-047A. Frames 004 and 005, 1994. 94-076. Frames 014 and 014, 1994. 97-537. Frames 008 and 009, 1997. Primary Sources Penrhyn Maps 2: Coytmor Demesne and part of the Coytmor Estate belonging to the Rt. Hon. Earl of Egmont (Undated). Penrhyn Maps 212: Plan of the Parish of Llanllechid, 1822. Penrhyn Maps 245: Plan of Coetmor Slate Quarry, rubbish banks and land in the Parish of Llanllechid, 1858. Tithe Map and Apportionment of the Parish of Llanllechid 1839. UB 2943 and 2944: Penrhyn Map of 1768. Secondary sources Bangor University Archives Caernarfon Archives and Record Office Gwynedd Historic Environment Record (HER)

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NMR Site Record Cards Brown D. H., 2007. Archaeological Archives: A guide to best practice in creation, compilation, transfer and curation. Archaeological Archives Forum British Geological Survey website. www.bgs.ac.uk. Chisholm, H. 1911. Encyclopaedia Britannica Dodd, C. R. 1844. The Peerage, Baronetage, and Knightage of Great Britain and Ireland English Heritage, 1991. Management of Archaeological Projects (MAP2) English Heritage, 2006. Management of Research Projects in the Historic Environment (MORPHE) English Heritage, 2011. The Settings of Heritage Assets The Institute for Archaeologists, 1994 (revised 2009) Standard and Guidance for Archaeological Desk-Based Assessment

Appendix I: Scheduled and Non-Scheduled Sites within 1km

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APPENDIX 1: SCHEDULED AND NON-SCHEDULED SITES WITHIN 1.0KM

Undesignated monument points within 1km of the proposed development area as listed on the Gwynedd HER

PRN Name Form Type Period 261 Pen y Gaer Hillfort, Cilfodan, Bethesda Earthwork Hillfort Roman

298 Hut Platform, W of Cae Llwyn Grydd Building - Ruined House platform Medieval

299 Hut Platform, S of Tal y Sarn Building - Ruined House platform Medieval

3674 Cock Pit, Llanllechid Placename Cockpit Unknown

5706 Sub-Circular Stone Structure, Bethesda Building - Ruined Building Unknown

5707 Field Enclosure/Structure, N of Bryn Meurig Other Structure Enclosure Unknown

5708 Cerrig Cannan, Bethesda Other Structure Cannon stone Post-Medieval

5709 Enclosure/Sheep Pen, Bethesda Other Structure Sheep pen Post-Medieval

5710 River Crossing Abuttment - Station Road, Bethesda

Other Structure Bridge abutment Post-Medieval

5711 Railway Underpass, No. Tanysgafell Other Structure Underpass Post-Medieval

5712 Quarry Scoops, N of Tanysgafell Other Structure Quarry Post-Medieval

5713 Site of 'Navy Oaks', Bangor Road Other Structure Named tree Post-Medieval

5714 Possible Structure, S of Parc Coetmor Other Structure Structure Unknown

5715 Tunnel, N of Bron Ogwen Other Structure Tunnel Post-Medieval

5716 Possible Well, Brynbella Crossroads Other Well Post-Medieval

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Structure

5717 Cerrig Cannan, Brynbella Crossroads Other Structure Cannon stone Post-Medieval

5740 Cerrig Cannan, Brynbella Crossroads Other Structure Boulder Post-Medieval

5744 Possible Hut Group, E of Tregarth Building - Ruined Hut circle settlement Prehistoric

5745 Possible Hut Group, N Parc y Moch Building - Ruined Hut circle settlement Prehistoric

5746 Possible Stone Structure, Parc y Moch Other Structure Structure Unknown

5747 Possible Sheepfold, Nr Ty'n y Clwt Isa Earthwork Sheep fold Unknown

5891 Early Field Remains, Llanllechid Other Structure Field system Unknown

11688 Pont Coetmor, over Afon Ogwen Bridge Post-Medieval 12070 Coed Uchaf Farmhouse Building Post-Medieval 15838 Bethesda and Llanllechid - Landscape Landscape Multi-Period 15877 Ogwen Valley - Landscape Landscape Multi-Period 20047 Slate Quarry, Coed Slate quarry Post-Medieval 20048 Slate Quarry, Coetmor Slate quarry Post-Medieval 20053 Slate Quarry, Dolgoch Slate quarry Post-Medieval 20058 Slate Quarry, Moel Faban Slate quarry Post-Medieval 20059 Slate Quarry, Pant Dreiniog Slate quarry Post-Medieval

20812 Mine, Lefelydd Pont Coetmor, Tregarth Other Structure Mine Post-Medieval

20821 Pont Sarnau Quarry, Bethesda Other Structure Quarry Post-Medieval

20822 Tan Ysgafell Quarry, Bethesda Other Structure Quarry Post-Medieval

21185 Route of 1801 Penrhyn Railway Other Structure Railway Post-Medieval

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21947 Felin Fawr, Bethesda Building - Roofed Slate mill Post-Medieval

29617 Copper Mine, Coed y Dinas Other Structure Copper mine Post-Medieval

30446 Boundary Wall, Bryn Arfon Other Structure Boundary wall Post-Medieval

30447 Slate and Wire Fence, Bryn Arfon Other Structure Slate fence Post-Medieval

30448 Field Boundary, NW of Bryn Arfon Earthwork Field boundary Post-Medieval 30489 Enclosures, Possible, W of Bryn Arfon Document Enclosure complex Unknown 31746 Garden, Bryn-Derwen Document Garden Post-Medieval 36224 Capel Jerusalem, Bethesda Building Chapel Post-Medieval

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Listed Buildings within 1km of the proposed development area.

LB Ref Name Grade 3663 Pont Coetmor (partly in Llanllechid and Bethesda communities) I 3670 Coed-uchaf II 4145 Capel Bethesda II 4153 Western Slab Mill at Felin Fawr Slate Works II 4154 Water Wheel House between slab mills at Felin Fawr Slate Works II 4155 Eastern Slab Mill at Felin Fawr Slate Works II 4156 Fitting and Repair Shop at Felin Fawr Slate Works II 4157 Foundry at Felin Fawr Slate Works II 4158 Water Mill & Wheel House at Felin Fawr Slate Works II 4159 Pont Coed-y-parc II

18383 Milestone S of Dol-goch II 18384 Capel Bethania II 18385 The Victoria Hotel II 18386 The War Memorial and surrounding wall. II 18387 Capel Jerusalem II 18388 Christ Church II 18389 II 18390 II 18391 II 18392 II 18393 II 18394 II 18395 The Douglas Arms Hotel including railings II 18397 Coetmor Farmhouse II 18398 Barn at Coetmor Farm II 18399 Outbuildings in farm-court at Coetmor Farm II 18400 Pont y Goetmor I 18409 II

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18414 II 18415 II 18416 II 18417 The King's Head Inn II 22975 Pont Coetmor (partly in Llandygai and Bethesda communities) II 23369 New Mill House II 23400 No.3 Tanysgafell II 23401 No.5 Tanysgafell II 23414 Fferm Tyn y Clwt II 23417 Bryn-Meurig II 23473 No.4 Tanysgafell II 23474 No.6 Tanysgafell II

Scheduled Ancient Monuments within 1km of the proposed development area

SAM no Name Type General Broad Class

CN297 Slate Gwaliau at Felin Fawr, Penrhyn Wall Post-Medieval/Modern Industrial

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Undesignated monument points within 1km of the proposed development area as listed on the NMR (RCAHMW)

NPRN Name Broad Class Type Period Form 570 Felin fawr slate works, ffrancon view, bethesda Industrial Slate processing works Post Medieval Complex

6733 Bethania welsh independent chapel, penrhyn terrace, bangor road, bethesda

Religious, Ritual and Funerary Chapel Post Medieval Building

6735 Bethesda independent chapel, high street Religious, Ritual and Funerary Chapel Post Medieval Building

6737 Carmel welsh independent chapel, cefn carmel, rachub, llanllechid


6739 Salem independent chapel, ffordd carneddi Religious, Ritual and Funerary Chapel Post Medieval Documents

6742 Bethel welsh baptist church, caellwyngrudd, ffordd hen banc, rachub, bethesda


6747 Brynteg calvinistic methodist chapel, brynteg place Religious, Ritual and Funerary Chapel Post Medieval Building

6749 Carneddi calvinistic methodist chapel , bethesda Religious, Ritual and Funerary Chapel Post Medieval Building

6751 Jerusalem welsh calvinistic methodist chapel, pant-glas road, bethesda

Religious, Ritual and Funerary Chapel

Post Medieval;19th Century Building

6753 Pantdreiniog calvinist methodist sunday school Religious, Ritual and Funerary Chapel Post Medieval Building

6754 Rachub chapel (calvinistic methodist;achub,yr), rachub Religious, Ritual and Funerary Chapel Post Medieval Documents

6756 Coed-moch methodist chapel (wesleyan) Religious, Ritual and Funerary Chapel Post Medieval Documents

6757 Salem wesleyan methodistchapel, caellwyngrudd, ffordd llanllechid, rachub


11947 Bethesda cemetery Religious, Ritual and Funerary Chapel Post Medieval Documents

11952 Tabernacl baptist chapel, penybryn road, bethesda Religious, Ritual and Chapel Post Medieval Building

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Funerary

11953 Siloam wesleyan methodist chapel, penybryn road, bethesda Religious, Ritual and Funerary Chapel Post Medieval Building

23786 Pont coetmor, over afon ogwen Transport Bridge Post Medieval? Not recorded

24676 Melin coetmor Agriculture and Subsistence Corn mill Post Medieval Documents

26303 Coed uchaf farmhouse Domestic Farmhouse Post Medieval? Not recorded 26412 Douglas arms hotel the Commercial Hotel Post Medieval? Not recorded 26689 John street Domestic Dwelling Post Medieval? Not recorded

43664 Christ church glanogwen Religious, Ritual and Funerary Church Medieval? Not recorded

86310 Bryn-derwen, garden, bethesda Gardens, Parks and Urban Spaces Garden Post Medieval Documents

86315 Bryn meurig, garden, bethesda Gardens, Parks and Urban Spaces Country house garden Post Medieval Documents

86338 Cloverly lodge, garden, craigside Gardens, Parks and Urban Spaces Country house garden Post Medieval Documents

86347 Coetmore hall, garden, bethesda Gardens, Parks and Urban Spaces Country house garden Post Medieval Documents

86348 Coetmore mount, garden, bethesda Gardens, Parks and Urban Spaces Country house garden Post Medieval Documents

300987 Pen-y-gaer, hillfort, cilfodan, bethesda Defence Hillfort Iron Age Earthwork 302806 Long huts, w. Of cae-llwyn-grydd Domestic Long hut Medieval Documents 308412 The victoria Domestic Public house Post Medieval Building 308413 John street, 10. Domestic House Post Medieval Building 309196 Ogwen terrace, 1-2, bethesda Domestic House Post Medieval Building 402775 Tanysgafell, no.3, bethesda Domestic Cottage Post Medieval Building 404774 War memorial, high street, bethesda Civil War memorial Modern Documents 406153 The kings head, 51, stryd fawr ; high street, bethseda Commercial Public house Post Medieval Documents 406185 Llangollen vaults, high street, bethesda, bangor COMMERCIAL Public house Post Medieval Documents 409723 Hendurnpike signal box, penrhyn railway Transport Railway signal box Post Building

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Medieval;19th Century

409724 Penrhyn railway, coed-y-parc bridge Transport Road bridge MODERN;20th Century Other Structure

409725 Tai'r stablau;slate mill cottages, coed-y-parc Domestic Terraced housing


411155 School;church house, behesda Education School Post Medieval Documents

411381 Grisiau cochion, bethesda Domestic

Terraced housing;workers housing Post Medieval Documents

415226 Bethesda town Civil Town

Post Medieval;19th Century Place Name

415255 Cilfoden powder magazine Industrial Powder magazine

Post Medieval;18th Century Documents

416939 Public hall (cinema), bethesda RECREATIONAL Cinema 20th Century Documents

417671 Tanysgrafell, no 4, Domestic Dwelling


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Historic Landscape Character Areas (HLCAs) within 1km of the proposed development area

HLCA PRN HLCA Name 12 15838 Bethesda and llanllechid 14 15840 Penrhyn quarry 32 15877 Ogwen valley 33 15858 Mynydd llandygai 36 15861 Unenclosed mountain (north carneddau) 37 15825 Enclosed fields above bethesda 38 15862 Fieldscape around llanllechid 40 15863 Sling

Appendix II: Definitions of further assessment and mitigatory measures

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APPENDIX 2: DEFINITIONS OF FURTHER ASSESSMENT AND MITIGATORY MEASURES 1. Definition of field evaluation techniques Field evaluation is sometimes necessary when the importance of an identified archaeological feature cannot be ascertained via an archaeological desk based assessment alone. There are several different techniques but the three most common are geophysical survey, trial trenching, and supervised metal detector survey: Geophysical survey This technique is a non-intrusive form of archaeological field evaluation. It utilises a magnetometer which detects differences within the earth’s magnetic field caused by the presence of iron in the soil. This iron often takes the form of magnetised iron oxides in the topsoil which have been re-deposited into lower archaeological features through cutting and backfill. A magnetometer can also detect iron artefacts within the soil and the presence of burnt stone material such as on hearths, kilns, and burnt mounds. Trial trenching Where a site is suspected to contain more subtle archaeological features such as pits, a geophysical survey may not be appropriate due to its lack on sensitivity in detecting these features. Indeed, trial trenching can also be utilised when anomalies have been identified during the geophysical survey and clarification is required in order to identify them. Trial trenches usually measure 20m by 2m although can vary ion size if targeting geophysical anomalies. Trenches are excavated using a mechanical tracked excavator and supervised by an archaeologist. The topsoil and subsoil are removed onto buried features or if absent, on to the natural glacial substrata. Any archaeological remains found are usually evaluated and recorded prior to backfilling of the trench, so that further site specific mitigatory recommendations can be made. Supervised Metal Detector Survey Some types of underlying substrata and bedrock can mask the results of investigation techniques such as geophysical survey. In such instances an archaeologically supervised metal detector survey can be undertaken. This involves the supervision of metal detectorists by a suitably qualified archaeologist and the spatial mapping of artefacts as they are discovered. This technique can give a geographical spread of metal finds and thus be indicative of ‘hotspot’ areas which may require further investigation by trial trenching for example. 2. Definition of Mitigatory Recommendations None: No further action is required. Detailed recording: A photographic and concise descriptive record is required, along with a digital survey. Basic recording: A photographic and basic descriptive record is required. Watching brief: Monitoring is required by a suitably qualified archaeologist during the proposed development. An archaeological watching brief is divided in to four categories according the IFA. 2001. Institute for Archaeologists 2001 Standard and Guidance for an archaeological watching brief:

36

• comprehensive (present during all ground disturbance)

• intensive (present during sensitive ground disturbance)

• intermittent (viewing the trenches after machining)

• partial (as and when seems appropriate).

Avoidance: These features should be avoided by the proposed development and any ancillary works including the establishment of compound and material lay-down areas. It may be necessary to surround the feature with a barrier and/or signage to avoid accidental damage. Reinstatement: These features should be reinstated to their original location and condition. Supervision by an archaeologist is required.

Appendix III: Stratascan Ltd Geophysical Survey

on a

rcha

eolo

gya e

Project name:

Bethesda, Gwynedd, North Wales

Client:

Aeon Archaeology

July 2013

Job ref:

J5576

Report author:

Thomas Richardson MSc

GEOPHYSICAL SURVEY REPORT

Project name:

Bethesda, Gwynedd, North Wales Client:

Aeon Archaeology

Job ref:

J5576

Field team:

Claire Stephens MA, Emma Watson BSc,

Finnegan Pope-Carter MSc

Techniques:

Detailed magnetic survey –

Gradiometry

Project manager:

Simon Haddrell BEng(Hons) AMBCS PIFA

Survey date:

4th-5th July

Report written By:


Site centred at:

SH 618 673

CAD illustrations by:


Post code:

LL57 3NN

Checked by:

David Elks MSc AIFA

Geophysical Survey Report Project Name: Bethesda, Gwynedd, North Wales Job ref: J5576 Client: Aeon Archaeology Date: July 2013 ______________________________________________________________________________________________________________________

_______________________________________________________ Page 1

TABLE OF CONTENTS

LIST OF FIGURES...................................................................................................................... 2

1 SUMMARY OF RESULTS .................................................................................................... 3

2 INTRODUCTION ............................................................................................................... 3

2.1 Background synopsis...............................................................................................................3

2.2 Site location ............................................................................................................................3

2.3 Description of site ...................................................................................................................3

2.4 Geology and soils ....................................................................................................................4

2.5 Site history and archaeological potential ...............................................................................4

2.6 Survey objectives ....................................................................................................................4

2.7 Survey methods ......................................................................................................................4

2.8 Processing, presentation and interpretation of results..........................................................5

2.8.1 Processing .......................................................................................................................5

2.8.2 Presentation of results and interpretation......................................................................5

3 RESULTS.......................................................................................................................... 5

3.1 Probable Archaeology.............................................................................................................6

3.2 Possible Archaeology ..............................................................................................................6

3.3 Other Anomalies .....................................................................................................................6

4 CONCLUSION ................................................................................................................... 7

5 REFERENCES .................................................................................................................... 8

APPENDIX A – METHODOLOGY & SURVEY EQUIPMENT.............................................................. 9

APPENDIX B – BASIC PRINCIPLES OF MAGNETIC SURVEY .......................................................... 10

APPENDIX C – GLOSSARY OF MAGNETIC ANOMALIES............................................................... 11


_______________________________________________________ Page 2

LIST OF FIGURES

Figure 01 1:25 000 Location plan of survey area

Figure 02 1:1000 Location of survey grids and referencing

Figure 03 1:1000 Plot of minimally processed gradiometer data

Figure 04 1:1000 Colour plot of gradiometer data showing extreme values

Figure 05 1:1000 Abstraction and interpretation of gradiometer anomalies


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1 SUMMARY OF RESULTS

A detailed gradiometry survey was conducted over approximately 2.5 hectares of grassland.

The survey at Bethesda did not identify any anomalies of probable archaeological origin. An

area of possible pitting and areas of possible quarrying have been identified; however these

anomalies could also have a geological origin. Much of the rest of the site is covered by

magnetic variation, likely of geological origin. The remaining anomalies are of modern origin,

relating to an underground service and modern ferrous objects.

2 INTRODUCTION

2.1 Background synopsis

Stratascan were commissioned to undertake a geophysical survey of an area outlined for

development. This survey forms part of an archaeological investigation being undertaken by

Aeon Archaeology.

2.2 Site location

The site is located near Bethesda at OS ref. SH 618 673.

2.3 Description of site

The survey area is approximately 2.5 hectares of grassland sloping steeply from north-east to

south-west, of which 1.8 hectares were surveyed. The southern field was overgrown so only

an area in the centre could be surveyed (see photo below). There were no other obstructions

to the survey area.


_____________________________________________________ Page 4

2.4 Geology and soils

The underlying geology is Llanberis Slates Formation - Sandstone (British Geological Survey

website). The drift geology is Till, Devensian - Diamicton (British Geological Survey website).

The overlying soils are known as Denbigh 1 which are typical Brown Earth soils. These consist

of fine loamy and fine silty soils over rock (Soil Survey of England and Wales, Sheet 2 Wales

England).

2.5 Site history and archaeological potential

A brief site history is provided by Aeon Archaeology:

The site is located within the Dyffryn Ogwen Registered Landscape of Outstanding Historic

Interest, designated primarily for the range and quality of its prehistoric and industrial

archaeology. In the immediate vicinity of the site, the recorded archaeological resource is

characterised by the latter, with several small quarries adjacent or near to the site. However,

prehistoric settlements (hillforts and hut circles) exist within the wider landscape, mainly on

the uplands that have been unaffected by later activity, but also at similar locations to the

application site.

Much of the lower slopes of the valley have experienced historic quarrying, agricultural

improvements, plantation and settlement, which have collectively had a significant impact on

the survival and visibility of any earlier archaeology. This is compounded by a lack of

significant development since the formal incorporation of archaeology within the planning

process, which may have provided the opportunity for archaeological discovery. In the 1990s,

two archaeological assessments were undertaken close to the application site, in connection

with a new water main(Gwynedd Archaeological Trust reports 69 and 125) and a proposed

bypass (GAT report 59). However, while these did result in new information, fieldwork was

limited. Both projects appear to have skirted the site and the reports contain no specific detail

relevant to it.

The application site is identified as greenfield land and, from historic mapping and its present

appearance, would appear to be the result of 18th/19th century estate improvements. It is

likely that these improvements will have removed any upstanding archaeology that formerly

existed at the site, but any below ground evidence is likely to relatively well-preserved; any

estate management and industrial features would also be of historic interest.

2.6 Survey objectives

The objective of the survey was to locate any features of possible archaeological origin in

order that they may be assessed prior to development.

2.7 Survey methods

This report and all fieldwork have been conducted in accordance with both the English

Heritage guidelines outlined in the document: Geophysical Survey in Archaeological Field


_____________________________________________________ Page 5

Evaluation, 2008 and with the Institute for Archaeologists document Standard and Guidance

for Archaeological Geophysical Survey.

Detailed magnetic survey (gradiometry) was used as an efficient and effective method of

locating archaeological anomalies. More information regarding this technique is included in

the Methodology section below and in Appendix A.

2.8 Processing, presentation and interpretation of results

2.8.1 Processing

Processing is performed using specialist software. This can emphasise various aspects

contained within the data but which are often not easily seen in the raw data. Basic processing

of the magnetic data involves 'flattening' the background levels with respect to adjacent

traverses and adjacent grids. Once the basic processing has flattened the background it is then

possible to carry out further processing which may include low pass filtering to reduce 'noise'

in the data and hence emphasise the archaeological or man-made anomalies.

The following schedule shows the basic processing carried out on all minimally processed

gradiometer data used in this report:

1. Destripe (Removes striping effects caused by zero-point discrepancies

between different sensors and walking directions)

2. Destagger (Removes zigzag effects caused by inconsistent walking speeds

on sloping, uneven or overgrown terrain)

2.8.2 Presentation of results and interpretation

The presentation of the data for each site involves a print-out of the minimally processed data

both as a greyscale plot and a colour plot showing extreme magnetic values, together with a

greyscale plot of the processed data. Magnetic anomalies have been identified and plotted

onto the 'Abstraction and Interpretation of Anomalies' drawing for the site.

3 RESULTS

The detailed magnetic gradiometer survey conducted at Bethesda has identified a number of

anomalies that have been characterised as being of a possible archaeological origin.

The difference between probable and possible archaeological origin is a confidence rating.

Features identified within the dataset that form recognisable archaeological patterns or seem

to be related to a deliberate historical act have been interpreted as being of a probable

archaeological origin.

Features of possible archaeological origin tend to be more amorphous anomalies which may

have similar magnetic attributes in terms of strength or polarity but are difficult to classify as

being archaeological or natural.


_____________________________________________________ Page 6

The following list of numbered anomalies refers to numerical labels on the interpretation

plots.

3.1 Probable Archaeology

No probable archaeology has been identified within the survey area.

3.2 Possible Archaeology

1 A number of small discrete positive anomalies in the centre of the northern

field. These anomalies are indicative of small former cut features, such as filled

in pits. These may be of archaeological origin, however a geological origin

cannot be ruled out.

2 Areas of magnetic variance in the northern field. These anomalies are

indicative of changes in the geology which may be related to historic

quarrying. However, it is not possible to determine whether the change in

geology is natural or man made.

3.3 Other Anomalies

3 Areas of magnetic variance across much of the site. These anomalies are likely

to be of geological or pedological origin.

4 A high amplitude bipolar linear anomaly running along the eastern boundary

of the northern field. This is indicative of an underground service.

5 Areas of magnetic disturbance are the result of substantial nearby ferrous

metal objects such as fences and underground services. These effects can

mask weaker archaeological anomalies, but on this site have not affected a

significant proportion of the area.

6 A number of magnetic ‘spikes’ (strong focussed values with associated

antipolar response) indicate ferrous metal objects. These are likely to be

modern rubbish.


_____________________________________________________ Page 7

4 CONCLUSION

The survey at Bethesda did not identify any anomalies of probable archaeological origin. An

area of possible pitting has been identified in the centre of the northern field, however these

anomalies could also be attributed to the geology that characterises much of the rest of the

site. Two areas in the northern field have been identified as possible areas of quarrying,

however it is not possible to determine whether these are natural or man made changes in

the geology. The remaining anomalies are not of archaeological significance, relating to

geological and modern features. An underground service has been identified in the northern

field, whilst the rest of the anomalies relate to modern ferrous objects.


_____________________________________________________ Page 8

5 REFERENCES

British Geological Survey South Sheet, 1977. Geological Survey Ten Mile Map, South Sheet First Edition

(Quaternary). Institute of Geological Sciences.

British Geological Survey, 2001. Geological Survey Ten Mile Map, South Sheet, Fourth Edition (Solid).

British Geological Society.

British Geological Survey, n.d., website:

(http://www.bgs.ac.uk/opengeoscience/home.html?Accordion1=1#maps) Geology of Britain viewer.

Soil Survey of England and Wales, 1983. Soils of England and Wales, Sheet 2 Wales England.

English Heritage, 2008. Geophysical Survey in Archaeological Field Evaluation.

Institute For Archaeologists. Standard and Guidance for Archaeological Geophysical Survey.

http://www.archaeologists.net/sites/default/files/nodefiles/Geophysics2010.pdf


_____________________________________________________ Page 9

APPENDIX A – METHODOLOGY & SURVEY EQUIPMENT

Grid locations

The location of the survey grids has been plotted together with the referencing information. Grids were

set out using a Leica 705auto Total Station and referenced to suitable topographic features around the

perimeter of the site or a Leica Smart Rover RTK GPS.

An RTK GPS (Real-time Kinematic Global Positioning System) can locate a point on the ground to a far

greater accuracy than a standard GPS unit. A standard GPS suffers from errors created by satellite orbit

errors, clock errors and atmospheric interference, resulting in an accuracy of 5m-10m. An RTK system

uses a single base station receiver and a number of mobile units. The base station re-broadcasts the

phase of the carrier it measured, and the mobile units compare their own phase measurements with

those they received from the base station. A SmartNet RTK GPS uses Ordnance Survey’s network of

over 100 fixed base stations to give an accuracy of around 0.01m.

Survey equipment and gradiometer configuration

Although the changes in the magnetic field resulting from differing features in the soil are usually weak,

changes as small as 0.2 nanoTeslas (nT) in an overall field strength of 48,000nT, can be accurately

detected using an appropriate instrument.

The mapping of the anomaly in a systematic manner will allow an estimate of the type of material

present beneath the surface. Strong magnetic anomalies will be generated by buried iron-based objects

or by kilns or hearths. More subtle anomalies such as pits and ditches can be seen if they contain more

humic material which is normally rich in magnetic iron oxides when compared with the subsoil.

To illustrate this point, the cutting and subsequent silting or backfilling of a ditch may result in a larger

volume of weakly magnetic material being accumulated in the trench compared to the undisturbed

subsoil. A weak magnetic anomaly should therefore appear in plan along the line of the ditch.

The magnetic survey was carried out using a dual sensor Grad601-2 Magnetic Gradiometer

manufactured by Bartington Instruments Ltd. The instrument consists of two fluxgates very accurately

aligned to nullify the effects of the Earth's magnetic field. Readings relate to the difference in localised

magnetic anomalies compared with the general magnetic background. The Grad601-2 consists of two

high stability fluxgate gradiometers suspended on a single frame. Each gradiometer has a 1m

separation between the sensing elements so enhancing the response to weak anomalies.

Sampling interval

Readings were taken at 0.25m centres along traverses 0.5m apart. This equates to 7200 sampling points

in a full 30m x 30m grid.

Depth of scan and resolution

The Grad 601-2 has a typical depth of penetration of 0.5m to 1.0m, though strongly magnetic objects

may be visible at greater depths. The collection of data at 0.25m centres provides an optimum

methodology for the task balancing cost and time with resolution.

Data capture

The readings are logged consecutively into the data logger which in turn is daily down- loaded into a

portable computer whilst on site. At the end of each site survey, data is transferred to the office for

processing and presentation.


_____________________________________________________ Page 10

APPENDIX B – BASIC PRINCIPLES OF MAGNETIC SURVEY

Detailed magnetic survey can be used to effectively define areas of past human activity by mapping

spatial variation and contrast in the magnetic properties of soil, subsoil and bedrock.

Weakly magnetic iron minerals are always present within the soil and areas of enhancement relate to

increases in magnetic susceptibility and permanently magnetised thermoremanent material.

Magnetic susceptibility relates to the induced magnetism of a material when in the presence of a

magnetic field. This magnetism can be considered as effectively permanent as it exists within the

Earth’s magnetic field. Magnetic susceptibility can become enhanced due to burning and complex

biological or fermentation processes.

Thermoremanence is a permanent magnetism acquired by iron minerals that, after heating to a specific

temperature known as the Curie Point, are effectively demagnetised followed by re-magnetisation by

the Earth’s magnetic field on cooling. Thermoremanent archaeological features can include hearths and

kilns and material such as brick and tile may be magnetised through the same process.

Silting and deliberate infilling of ditches and pits with magnetically enhanced soil creates a relative

contrast against the much lower levels of magnetism within the subsoil into which the feature is cut.

Systematic mapping of magnetic anomalies will produce linear and discrete areas of enhancement

allowing assessment and characterisation of subsurface features. Material such as subsoil and non-

magnetic bedrock used to create former earthworks and walls may be mapped as areas of lower

enhancement compared to surrounding soils.

Magnetic survey is carried out using a fluxgate gradiometer which is a passive instrument consisting of

two sensors mounted vertically 1m apart. The instrument is carried about 30cm above the ground

surface and the top sensor measures the Earth’s magnetic field whilst the lower sensor measures the

same field but is also more affected by any localised buried field. The difference between the two

sensors will relate to the strength of a magnetic field created by a buried feature, if no field is present

the difference will be close to zero as the magnetic field measured by both sensors will be the same.

Factors affecting the magnetic survey may include soil type, local geology, previous human activity,

disturbance from modern services etc.


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APPENDIX C – GLOSSARY OF MAGNETIC ANOMALIES

Bipolar

A bipolar anomaly is one that is composed of both a positive response and a

negative response. It can be made up of any number of positive responses and

negative responses. For example a pipeline consisting of alternating positive and

negative anomalies is said to be bipolar. See also dipolar which has only one

area of each polarity. The interpretation of the anomaly will depend on the

magnitude of the magnetic field strength. A weak response may be caused by a

clay field drain while a strong response will probably be caused by a metallic

service.

Dipolar

This consists of a single positive anomaly with an associated negative response.

There should be no separation between the two polarities of response. These

responses will be created by a single feature. The interpretation of the anomaly

will depend on the magnitude of the magnetic measurements. A very strong

anomaly is likely to be caused by a ferrous object.

Positive anomaly with associated negative response

See bipolar and dipolar.

Positive linear

A linear response which is entirely positive in polarity. These are usually related

to in-filled cut features where the fill material is magnetically enhanced

compared to the surrounding matrix. They can be caused by ditches of an

archaeological origin, but also former field boundaries, ploughing activity and

some may even have a natural origin.


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Positive linear anomaly with associated negative response

A positive linear anomaly which has a negative anomaly located adjacently.

This will be caused by a single feature. In the example shown this is likely to be

a single length of wire/cable probably relating to a modern service.

Magnetically weaker responses may relate to earthwork style features and

field boundaries.

Positive point/area

These are generally spatially small responses, perhaps covering just 3 or 4

reading nodes. They are entirely positive in polarity. Similar to positive linear

anomalies they are generally caused by in-filled cut features. These include pits

of an archaeological origin, possible tree bowls or other naturally occurring

depressions in the ground.

Magnetic debris

Magnetic debris consists of numerous dipolar responses spread over an area. If

the amplitude of response is low (+/-3nT) then the origin is likely to represent

general ground disturbance with no clear cause, it may be related to something

as simple as an area of dug or mixed earth. A stronger anomaly (+/-250nT) is

more indicative of a spread of ferrous debris. Moderately strong anomalies may

be the result of a spread of thermoremanent material such as bricks or ash.

Magnetic disturbance

Magnetic disturbance is high amplitude and can be composed of either a bipolar

anomaly, or a single polarity response. It is essentially associated with magnetic

interference from modern ferrous structures such as fencing, vehicles or

buildings, and as a result is commonly found around the perimeter of a site near

to boundary fences.


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Negative linear

A linear response which is entirely negative in polarity. These are generally

caused by earthen banks where material with a lower magnetic magnitude

relative the background top soil is built up. See also ploughing activity.

Negative point/area

Opposite to positive point anomalies these responses may be caused by raised areas or earthen banks. These

could be of an archaeological origin or may have a natural origin.

Ploughing activity

Ploughing activity can often be visualised by a series of parallel linear anomalies.

These can be of either positive polarity or negative polarity depending on site

specifics. It can be difficult to distinguish between ancient ploughing and more

modern ploughing, clues such as the separation of each linear, straightness,

strength of response and cross cutting relationships can be used to aid this,

although none of these can be guaranteed to differentiate between different

phases of activity.

Polarity

Term used to describe the measurement of the magnetic response. An anomaly can have a positive polarity

(values above 0nT) and/or a negative polarity (values below 0nT).

Strength of response

The amplitude of a magnetic response is an important factor in assigning an interpretation to a particular

anomaly. For example a positive anomaly covering a 10m2 area may have values up to around 3000nT, in

which case it is likely to be caused by modern magnetic interference. However, the same size and shaped

anomaly but with values up to only 4nT may have a natural origin. Colour plots are used to show the amplitude

of response.


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Thermoremanent response

A feature which has been subject to heat may result in it acquiring a magnetic field. This can be anything up to

approximately +/-100 nT in value. These features include clay fired drains, brick, bonfires, kilns, hearths and

even pottery. If the heat application has occurred in situ (e.g. a kiln) then the response is likely to be bipolar

compared to if the heated objects have been disturbed and moved relative to each other, in which case they

are more likely to take an irregular form and may display a debris style response (e.g. ash).

Weak background variations

Weakly magnetic wide scale variations within the data can sometimes be seen

within sites. These usually have no specific structure but can often appear curvy

and sinuous in form. They are likely to be the result of natural features, such as

soil creep, dried up (or seasonal) streams. They can also be caused by changes in

the underlying geology or soil type which may contain unpredictable

distributions of magnetic minerals, and are usually apparent in several

locations across a site.

A3

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VINEYARD HOUSE

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WR8 0SA

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AND ENGINEERING

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AEON ARCHAEOLOGY

J5576

BETHESDA, GWYNEDD, NORTH

WALES

LOCATION PLAN OF SURVEY AREA

SH 618 673

Site centred on NGR

Reproduced from Ordnance Survey's

1:25 000 map of 1998 with the

permission of the controller of Her

Majesty's Stationery Office.

Crown Copyright reserved.

Licence No: AL 50125A

Licencee:

Stratascan Ltd.

Vineyard House

Upper Hook Road

Upton Upon Severn

WR8 0SA

OS 100km square = SH

66

67

68

69

© Stratascan Ltd - 2013

60 61 62 63 64

65

N

Survey Area

0m 500 1000m

Survey Area

A

B

C

D

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LOCATION OF SURVEY GRIDS AND

REFERENCING

OS GRID REFERENCES

A

B

C

D

261797.82, 367247.88

261902.76, 367306.09

261841.468, 367306.09

261920.17, 367212.83

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PLOT OF MINIMALLY PROCESSED

GRADIOMETER DATA

Plotting parameters

Maximum +5nT (black)

Minimum -5nT (white)

-5nT +5nT

+5nT

-5nT

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COLOUR PLOT OF GRADIOMETER

DATA SHOWING EXTREME VALUES

Plotting parameters

Maximum +100nT (red)

Minimum -100nT (blue)

+100nT

-100nT

-10nT

-10nT

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ABSTRACTION AND INTERPRETATION

OF GRADIOMETER ANOMALIES

Closely spaced parallel linear anomalies - probably

related to agricultural activity such as ploughing

Magnetic disturbance associated with nearby metal

object such as service or field boundary

Linear anomaly - probably related to pipe, cable or

other modern service

Linear anomaly - possibly related to land drain

Scattered magnetic debris

Area of amorphous magnetic variation - probable

natural (e.g. geological or pedological) origin

OTHER ANOMALIES

POSSIBLE ARCHAEOLOGY

Positive anomaly / weak positive anomaly - probable

cut feature of archaeological origin

PROBABLE ARCHAEOLOGY

Negative anomaly / weak negative anomaly - probable

bank or earthwork of archaeological origin

Widely spaced curving parallel linear anomalies -

probably related to ridge-and-furrow

KEY

Moderate strength discrete anomaly - probable

thermoremanent feature

Positive anomaly / weak positive anomaly - possible cut

feature of archaeological origin

Negative anomaly / weak negative anomaly - possible

bank or earthwork of archaeological origin

Magnetic spike - probable ferrous object

Job No.

J5576

1:1000

0m 10 20 30 40 50

Area of amorphous magnetic variation - possibly related

to historic quarrying

STRATASCAN LTD

Vineyard House Upper Hook Road Upton upon Severn

Worcestershire WR8 0SA United Kingdom

T:0 1684 592266 F: 01684 594142

[email protected] www.stratascan.co.uk

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