TECHNICAL REPORT WA/88/2 (North ) thematic geological mapping S 14 G Campbell and B A Hains Contributors M G Culshaw, J A Crummy and M A Lewis

BRITISH GEOLOGICAL SURVEY

TECHNICAL REPORT WA/88/2 Onshore Geology Series Cover pcover Well-bedded limestone of the Limestoneis ex- posed in Brodlas quarry, now disused. The main face[SJ 1875 73151 is here seen fromthe south- west. The unusualnature of the bedding at this stratigraphic hor- izon is particularlywell displayed, with several prominent low-angle discordant bedding-plane contacts. Deeside () thematic Back cover 1 To the south of Waen Brodlas quarry [SJ 186 7321 the moundytopography comprises geologicalmapping deposits of made ground associated with the numerous shafts and trial pits that characterise muchof Mountain. Most weresunk during the nineteenthcentury in S D G Campbell and B A Hains the search for lead andcopper veins. 2 Beautifullypreserved fossil cri- Contributors noids are exposed in a disused quarry [SJ 188 7251 on Halkyn M G Culshaw and J A Crummy engineering geology Mountain. The rock-type was main- ly usedly for ornamental purposes. M A Lewis hydrogeology 3 A spectacularly well-preserved trace-fossil burrow system(Zoophy- cos) exposed in PantQuarry [SJ 201 7021, in which limestone isworked. 4 Sand and gravel is worked in the Rhosemor pit [SJ 216 6701, here seen fromthe north. 5 The Loggerheads CountryPark is a Siteof Special Scientific Interest. Large-scale bedding typicalof the Loggerheads Limestone dips gently to the east in the west-facing scarp. 6 Well-bedded and fmely laminated chertsare exposed in the disused Pen yr Henblas quarries [SJ 191 7273.

Geographic index , North Wales,

Subject index Thematic maps, resources, geo- technics, hydrogeology, minerals, coal, aggregate, ground stability

This report was produced under contract to the Department of the Environment on behalf of the Welsh Office, but the views expressed in it arenot necessarily those of the Department nor of the Offke.

Bibliographic reference Campbell, S D G, and Hains, B A. 1988. Deeside (North Wales) thematic geological mapping. British Geological Survey Technical Report WAl88i2.

0 Crowncopyright 1988 Keyworth,Nottingham British Geological Survey 1988 BRITISH GEOLOGICAL SURVEY

The full range of Survey publications is available through the Keyworth, Nottingham NG12 5GG Sales Desks at Keyworth and Murchison House, Edinburgh. s Plumtree (06077) 6111 Telex 378173 BGSKEY G Selected items can be bought at theBGS Information Fax e 060 77-6602 Office, and orders are accepted here for all publications. The adjacent Geological Museum bookshop stocksthe more popular Murchison House, West Mains Road, Edinburgh EH93LA books for sale over the counter. Most BGS books and reports . .. 031-6671000Telex727343 SEISED G . .. - are listed in HMSO’s Sectional List 45, and can be bought from e Fax e 031-668 2683 HMSO and through HMSO agents and retailers. Maps are listed in theBGS Map Catalogue and the ’s London Information Office at theGeological Museum, Trade Catalogue, and can be bought from Ordnance Survey Exhibition Road, South Kensington, LondonSW7 2DE agents as well as from BGS. e 01-5894090 Telex8812180 GEOSCI G The BritishGeological Survey carries out the geological survey 01-9389056157 Fax 3 01-584 8270 of and Northern Ireland (the latter as an agency service for the government of Northern Ireland), and of the surrounding continental shelfi as well as its basic research 64 Gray’s Inn Road, London WClX 8NG projects. It also undertakes programmes of British technical aid e 01-242 4531 in geology in developing countries as arranged by the Overseas Development Administration. 19 Grange Terrace, Edinburgh EH9 2LF e 031-6671000Telex727343 SEISED G The British Geological Survey is a component body of the Natural Environment Research Council. St Just, 30 Pennsylvania Road, Exeter EX4 6BX s Exeter (0392) 78312 Maps and diagrams in thisbook use topography based on Ordnance Survey mapping Bryn Eithyn Hall, Llanfarian, Aberystwyth, Dyfed SY23 4BY 3 Aberystwyth (0970) 611038

Windsor Court, Windsor Terrace, Newcastle upon Tyne NE2 4HB CS 091-2817088 Fax e 091-2819016

Geological Survey of Northern Ireland, 20 College Gardens, Belfast BT9 6BS e Belfast (0232) 666595and 666752

Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB e Wallingford(0491) 38800 Telex 849365 HYDRO G Fax 3 0491-32256

Parent Body Natural Environment Research Council Polaris House, North Star Avenue, Swindon, Wiltshire SN2 1EU e Swindon(0793) 40101 Telex 444293 ENVRE G Fax e 0793441652 CONTENTS Appendices A. List of British Geological Surveyopen-file ExecutiveSummary 1 reports, 1: 10 OOO/lO 560 geological maps and Notes to the userand limitations 4 palaeontological reports produced as part of the 99 Introduction 7 project B. Geotechnical tests quoted in the database,and Objectives7 their applications 10 1 The useof this report 7 List of boreholes 105 Data sources used in the report 8 C. List of shafts sunk for coal 132 Constituent parts of the results 9 D. E. Selective list of shaftsand adits identified as Geographicaland planning background 9 being open surface,at theat time of Geographicalbackground 9 survey 152 Planning background1 1 F. Logsof boreholes sunk as part of theproject to prove sandand gravel resources with Geological informationrelevant to planning 12 derivedparticle size data 155 Mineralextraction and resources 12 Engineering geology 14 Figures Water resources 15 1. Sketch-map of the study area showing its Geological Sequence 17 regional setting 5 2. Sketch-map showing the component Description of thematic geological maps 18 Notes aboutthe topographic base 18 1:lO OOO/lO 560 sheets of the study area, the outlines of the earlier County Sheet Grid, and List of ThematicElements 18 selected planningfeatures 6 Map 1 Bedrock Geology 18 - 3. Topography, drainage and chief towns of the Map 2 Superficial (Unconsolidated) - studyarea 10 deposits 20 4. Simplified geological map of the study area 19 Map 3 Boreholes, Rockhead and thickness - 5. Detailed map (Scale 1:lO 560) of the of Superficialdeposits 22 distribution of shafts and trial pits on Halkyn - Map 4 Mining activities; - Mountain Coal/Metalliferous 23 a) The area between Pant and Map 5 Resources (Bedrock) except - - Pant-y-pwll-dwr 25 Coal/Metalliferous 29 b) The area between Pen yr Henblas and Map 6 - Resources - Sand and Gravel 34 26 Map 7 Hydrogeology and Water Supply 35 - 6. Detailed map (Scale 1:lO 560) of the EngineeringGeology 37 Loggerheads Country Park and Thegeotechnical database 37 Cefn-Mawr/Coed Pwll-y- blawd Site of Special Engineering classification of the rocks ScientificInterest 27 and soils 38 7. Plasticity Diagram for Weathered Mudstones Engineering geology of the bedrock and Shales 42 formations(rock) 38 8. Plasticity Diagram for Head, Alluvial and Engineering geology of the superficial Estuarine Alluvial Cohesive Soils 52 (unconsolidated)deposits (soils) 50 9. Plasticity Diagram for Till (Boulder Clay) and Groupings of superficial deposits in other Glacial Cohesive Soils 56 engineering terms 64 10.Generalised geological sequence of the study Engineering problems associated with area 74 superficial(unconsolidated) deposits 65 1 1 .Detailed correlation of the Limestone sequences of the main working quarries (Graphic logs Summary of Geology 73 compiled by S D G Campbell and J R Davies) Conclusionsand Recommendations 85 a) Limestone correlation 76 b) Loggerheads Limestone correlation, with an References 91 inset of the position of the .quarry sites 77 Glossary 94 12.Correlation of the Productive Coal Measures (Westphalian A-C) 8 1 Tables Accompanying documents 1. ‘Correlation’ of Coal Seam Nomenclature for Theaccompanying maps at 1:25 000 scale and thenorthern ‘ Coalfield’ 28 printed on amended Ordnance Survey topographic 2. Active limestone quarries at the time of bases, are available separately. The full set is part survey 31 of BGS Research Report WA/88/2 comprising the Summary of mechanical and chemical property 3. following volumes: datafrom limestones 32 4. Summary geotechnical data for Mudstones of Deeside (North Wales) Thematic Geological Buckley Formation (Highly to Completely Mapping - Report Weathered) 43 Map 1 of Bedrock Geology 5. Summary geotechnical data for Map 2 of Superficial (Unconsolidated) deposits Shales/Mudstones of Productive Coal Measures Map 3 of Boreholes, Rockhead and thickness of (Fresh to Slightly Weathered) 44 Superficial deposits 6. Summary geotechnical data for Map 4 of Mining activities; CoallMetalliferous Shales/Mudstones of Productive Coal Measures Map 5 of Resources (Bedrock) - except (Moderately to Highly Weathered) 45 Coal/Metalliferous 7. Summary geotechnical data for Map 6 of Resources - Sand and Gravel Shales/Mudstones of Productive Coal Measures Map 7 of Hydrogeology and Water Supply (Completely Weathered to Residual Soil) 46 8. Summary geotechnical data for Shales of Note: it is emphasised thatthe maps associated Halkyn Formation (Fresh to Slightly with thisreport should be used for preliminary Weathered) 47 studies only and are not to be used as a substitute 9. Summary geotechnical data for Shales of for on-site investigations Halkyn Formation (Moderately to Highly Weathered) 48 10.Summary geotechnical data for Shales of Halkyn Formation (Completely Weathered to Residual Soil) 49 1 1.Summary geotechnical data for Peat 51 12.Summary geotechnical data for Alluvium; Clay 53 13.Summary geotechnical data for Alluvium (mainly clayey, silty fine sand) 54 14.Summary geotechnical data for Estuarine Alluvium; Clay 57 15.Summary geotechnical data for Estuarine Alluvium (mainly clayey, silty fine sand) 58 16.Summary geotechnical data for Estuarine Alluvium; Sand 59 17.Summary geotechnical data for Lacustrine Alluvium 60 1&Summary geotechnical data for Heterogeneous Deposits (Head) 61 19.Summary geotechnical data for Glacial Sand and Gravel (or Sandy Gravel associated with Till)62 20.Summary geotechnical data for Glacial Sand - stratified63 21.Summary geotechnical data for Till (Boulder Clay) 65 22.Summary geotechnical data for Till (Boulder Clay); Selected data 66 23.Foundation loading criteria for Estuarine Alluvium at different individual sites within the Deeside area 68 24.Foundation loading criteria for Glacial Sand and Gravel at different individual sites within the Deeside area 70 25.Foundation loading criteria for Till (Boulder Clay) at different individual sites within the Deeside area 71 PREFACE

Thisaccount describes the geology of the Deeside area, encompassing approximately 265 km2. Itcovers the Ordnance Survey 1:lO 000 Sheets SJ 26 NW, NE, SW, SE; SJ 27 SW; parts of SJ 17 NE; SJ 27NW, NE, SE; SJ 36 NW,SW; SJ 37 SW; and parts of the 1:lO 560 Sheets SJ 17SE and SJ 16 NE, SE. Thearea lies withinthe 1:50 000 Geological Sheets 96 () and 108 (Flint). Thedistrict was first surveyed atthe six-inch scale by AStrahan and C E DeRance between 1879-85 withan accompanying descriptive memoir by AStrahan published in 1890. Aresurvey of the Coal Measure sequences was undertaken by CB Wedd, W B R King, H H Thomas and G W Lamplugh in 1910-13. An accompanying memoir by C B Wedd and W B R King was published in 1924. A memoir by B Smith describing aspects of the metalliferous mining and mineral resources of the region was published in 1921. The present study was commissioned by the Department of the Environment on behalf of the Welsh Office.Funding was providedjointly by theDepartment of the Environmentand the British Geological Survey. Its objectives were to produce new geological maps at 1: 10 OOO/lO 560 scale, and together with other available surface and subsurfacedata, to presentthe geological informationrelevant to land use planning, developmentand redevelopment inthe form of aset of thematic geological maps at 1:25 000 scale with an accompanying explanatoryreport. Particular emphasis has been placed on superficial deposits, underground workings andmineral resources. Alimited shallow borehole programme was carried out to prove sand and gravel deposits. Further syntheses were undertaken by M G Culshaw, J ACrummy and J R Hallam of the engineeringproperties of both thebedrock and superficial deposits of the area, and of its hydrogeology by M A Lewis. The mapping was undertaken by Drs S D G Campbell, J R Davies, B A Hains and D Wilson. Dr N J Riley provided palaeontological support. Thetext was word-processed by Mrs L M Ellis. TheProject Leader was Dr Hains. Dr R A €3 Bazley, Regional Geologist for Wales,was the Nominated Officerfor the British Geological Survey,and Mr D B Courtier, Welsh Office, was theNominated Officer for the Secretary of State. The ready cooperation of landowners, tenants, and quarry companies during this survey and of local and regional authorities,and other holders of data is gratefully acknowledged. In particular we thank , Alyn and Deeside District Council, Delyn District Council, Glyndar District Council, British Coal, the Welsh Development Agency, WimpeyP.L.C., AlfredMcAlpine Quarries Ltd., Tilcon Ltd., North West Aggregates Ltd., Castle CementLtd., Welsh Aggregates Ltd.,Pioneer Aggregates (U.K.)Ltd., Thomas Dodd and Son Ltd., andButterley Brick Ltd. We also acknowledge many geological and geotechnical consultantsand in particular Wardell Armstrong and Partners.

Deeside (North Wales) Thematic Geological Mapping I

EXECUTIVE SUMMARY engineering problems of the deposits; and hydrogeological characteristics of thearea, its Thisstudy was commissioned by theDepartment water resources and problems of aquifer of the Environment on behalf of the Welsh Office protectionwith respect, for example, to waste and was funded jointly by the Department of the disposal. Environmentand the British Geological Survey. Its principalaim was toproduce a synthesis of Theinformation used inthe report was acquired geological information relevant to the planning of essentially twoin ways. Firstly,a revision land-use and developmentin the Deeside area of geological survey of entirethe area was Clwyd (North Wales). Theintention is that this undertaken at a scale of 1:lO OOO/lO 560 between reportpresents thatinformation style ain 1985 and 1987. Informationfrom previous comprehensible to those involved in planning and surveys, in the archives of theBritish Geological development and little geological knowledge is Survey, was also used and aset of maps and requiredto be ableto use it. Much of the relateddescriptive reports were produced(these information is providedon a series of seven are listed inAppendix A). Secondly, data was thematic maps, each of whichconcentrates on a soughtand compiled from varioussources, most specificaspect of the geology. In addition to the notablyfrom central government and local informationcontained in the report, sources of authorities,British Coal, the Welsh Development other more detailed data are indicated. Agency, WelshWater, theCentral Electricity Generating Board and several geological and The study area is approximately 265 km2 in size. geotechnical consultants. This data was mainly in It lies withinthe area covered by theBritish theform of site-investigationreports, borehole Geological Survey 150 000 geological sheets 96 logs andthe results of geotechnical tests. Much (Liverpool) and 108 (Flint). It includes themajor of it,and in particular that related to opencast towns of Flint, Connah’s Quay, Mold, Buckley coal site-investigation(provided by the Opencast and Holywell. The area stretches from the eastern Executive of British Coal), is confidential. margin of the Clwydian Hills in the southwest, to However, information has been derivedfrom the Dee Estuaryand the boundary with these confidential boreholes and used, for inthe northeast. The highestpoint (441 m) is in example, in the construction of rockhead contours the Clwydian Hills andthere is gradual a presented on the thematic thepresented on maps. A reduction in the height of the topography, moving comprehensive list of boreholes consulted is given from west to east. Thedrainage patterns are inAppendix C. Othersources of data used influenced by thedisposition of scarpfeatures included: the results of a limitedtest-drilling related to theoutcrop of bedrock. The main programme (see Appendix F) carriedout part rivers of the area are the Alyn and the Dee. as of thestudy to prove andquantitatively assess The economy of thearea is mixed, with sandand gravel deposits; andpublished scientific agriculturepredominating theincentral and literature and other unpublished reports. western parts, whereas industry is concentrated Seven thematic geological maps, at a scale of around the larger towns and particularly along the 1:25 000, are provided and described. In addition, coastal stripbordering the . The reporta of theengineering characteristics of Shottonsteelworks andneighbouring modern bedrockandsuperficial deposits, based on industrialestates occupy large sites thein available geotechnicaldata, is given. The geology northeast.Mineral extractive industries have been of thearea isalso described indetail, including important in the past and, though more limited in generalfeatures of theformations and members, theirrange today, they continue to play a very interpretations of the modes and environmentsin important rdle in the local economy. which strata were deposited, the regional structure Themain objective of thereport is to provide and the nature of mineralisation. geological information which isof direct concern Therelevance to planners and developers of the to planners and developers and it concentrates on various types of geological informationpresented four main aspects: thenature and extent of is outlined. The most significantmineral mineral resources; geological constraints, including resources of thearea are limestone, sand and both naturalhazards (e.g. landslips)and those gravel, and coal. Theformer two arecurrently related to former mining and quarryingactivity the basisof majorextractive industries. Coal (e.g. subsidence and collapse related to shafts and mining was formerlyimportant but no miningor mine workings); engineering characteristics of the opencasting is active at present. Thereare also variousdeposits ator nearsurface and related 2 Deeside (North Wales) ThematicGeological Mapping several lesser resources, including sandstone, varyingthickness of superficial deposits. Limited chert,metalliferous ores, brickclay and refractory structuraldata are given, includingthe more clay, mouldingsand and calcspar. Of these, only importantfaults and the orientation and relative brickclay and mouldingsand arecurrently dip of strata. extracted.Knowledge of theareal extent, and Thesuperficial deposits map indicates their qualitativeand quantitative assessments of the distribution at surface, where they exceed 1 metre resources establishes a basis for their efficient and in thickness. It does notdisplay their variation rationalexploitation. Sterilisation of valuable with depth. Information on the form of rockhead resources can be avoided, andalternative sites of (theinterface between bedrock and superficial extractionidentified. Detailed subdivision and deposits) is given inthe form of rockhead mapping of thestrata (e.g. the limestones) contours. constrainthe distribution of specific resource types with distinct characteristics. Themap of boreholes shows the sitesonly of non-confidential boreholes for whichthe British As important as the mineralresources themselves Geological Survey holds information.Those for arethe consequences of theirearlier extraction, which geotechnical test data are also available are andparticularin theeffects of coal and highlighted. Where known,the thickness of the metalliferousmining. Thus, shaft sitespresent superficial deposits and the level of rockheadare common hazards, while constraintsareason shown. From these dataand, in addition, using known haveto been underminedare also data from confidential sources, rockhead contours important.Planners and engineers are inevitably have been constructed.A full list of concernedwith thefoundation properties and non-confidential boreholes with further details is stability of sites. Analysis of available included in Appendix C. geotechnical data indicatesthe ranges of engineering properties of surface and near surface Thethematic element of mininginformation deposits,such as theircompressibility, the concentrates on features associated withcoal and likelihood of differential subsidence problems, metalliferousmining, and a small area of andtheir likely behaviour if excavated. The cementstone mining. Thus,the loci of shaftsand bedrocksuperficialand deposits can be adits(those capped being differentiated)and the categorised in terms of theirgeneral cohesion, distribution of related made ground and backfilled consolidation and heterogeneity.Therelative opencastaresites shown. In areas of importance of theaquifers in the area highlights metalliferousmining, the position atsurface of those most needful of protection when, for the principal worked veins are indicated. In areas example, planning sites for waste disposal. of coal mining,theextent of underground workings for whichrecords exist are shown,and The seven thematic maps contain generalised and areas undermined by workingsin more than one selective, ratherthanfullycomprehensive, seam aredistinguished. This aspect is particularly informationregarding specific themes. They are problematicsince much of themining preceded presented at 1:25 000 scale, whereas they are the age of statutory regulations on recording mine largely based on 1: 10 10 560 and yet more OOO/ workings. Consequently,the workings shown detailed maps. Consequently,there is inevitablya represent only a proportion of those likely to have significantinformation loss associated with the taken place. Inareas of especially intense mine reduction in scale. As with all of the information workings (e.g. HalkynMountain), shafts were presentedin thereport, they should not be categorised qualitatively according to their relative regarded assubstitute fora specific hazardpotential, and detailed figures showing site-investigations. these shaftsare included within the report. Some Thethematic maps concentrate on sevenspecific of theinadequately treated oruntreated shafts themes: bedrock geology; superficial whichare open at surface are listed inAppendix (unconsolidated) . deposits; non-confidential E. Appendix D gives acomprehensive list with borehole sites,rockhead and drift thickness further details of all knownshafts and adits information;mining information (related to coal related to coal mining. Thenature and depth of andmetalliferous ores); bedrock resources; sand coal mining has not been constrained. More and gravel resources; hydrogeological features. recent workings arelikely to have used longwall methods but earlier(and oftenunrecorded) The map of bedrock geology indicates the surface workings would have been likely to use pillar and extent of thevarious formations (bedrock units) stall techniques.Active subsidence was observed both as exposed and as interpretedbeneath a Deeside (North Wales) Thematic Geological Mapping 3 during the field survey and has been recorded in overburdenare described more rigorously in recent times in relation to collapse of shafts rather geological terms inthe Summary of Geology. than to underground workings. Thecourses of Thissection describes the variationsin thickness the drainage of the Halkyn-Holywell mine andinternal characteristics of the constituent drainage scheme are also shown on this map. formations of the area. In addition, interpretations of themode andenvironment of Dataon bedrock resources and sand and gravel deposition of the sediments are made. Patterns of resources are shown on separate maps. That of regularvertical repetitions of rock types bedrockresources indicates those areaswhere (cyclicity) andthe recognition of temporally resources (excluding coal andmetalliferous ores) equivalentsedimentary rocks (correlation)are areavailable atsurface or with onlylimited discussed. The sequence ranges in age from superficialoverburden. The sand and gravel Silurian to Permo-Triassic (and locally Tertiary), resource map similarly defines the distribution of while the superficial deposits are of Quaternary to theresource where it occurs ator nearsurface. Recent age. Thearea is dominated by Some information on the thickness of the deposits sedimentary rocks of Carboniferous age, which lie andits variability are provided on the mapface. unconformably on Silurianstrata, andare Test results of limiteda drilling programme themselves unconformablyoverlain by undertaken to prove these deposits in the north of Permo-TriassicCarboniferousThestrata. thearea are in Appendix F. Crudeestimates of sequenceincludes approximately 650 m of the tonnage of potential resources were made. Dinantian limestones whichare in part cyclic. The hydrogeology map shows theoutcrops of the Theyare overlain by up to 350 m of Namurian principalaquifers and the locations of springs, sandstones, chert, siltstones and mudstones. These wells and boreholes licensed to abstract turnarein succeeded by the Westphalian groundwater.Groundwater level contours are Productive Coal Measures (up to 450 m) which represented inthe Kinnerton Sandstone. Waste are characterised by cyclic repetition of mudstone, disposal sites are also shown since these represent siltstone, sandstone, seatearthand coal. Coals in potentialrisks to groundwaterquality. However, excess of 4 m in thickness occur within the area. most of thewater used in thearea comes from The Buckley Formation and Marl, both of surface and groundwater sources outside the area. which lack significant coal seams, overlie and are in part laterally equivalent to the Productive Coal As thecoverage of available geotechnical data is very patchy, no maps of engineering geology were Measures. In general, coal seams are more laterallycontinuous within the lower part consideredworthwhile. However, the ranges of (Westphalian A) of theProductive Coal Measures geotechnicalproperties of the various bedrock thanwithin the overlying Westphalian B, though formations andsuperficial deposits are discussed the latter includes the Main and Hollin Coals, two withinthereport. Hence the suitability for of the thickest and most extensively worked seams foundations,potentialbackfill materials, in the area. behaviour of excavations and stability of each of thedeposits are discussed andpotential problems Thereport concludes with a list of specific highlighted. Much of the information is tabulated problems and factors to be considered in planning and/orpresented infigures within the report. and development. It also includes a reference list, Descriptions of thegeotechnical tests used to anda glossary of terms used. Copies of this providethe data considered in thereport are report and its accompanying maps can be obtained given in Appendix B. from theBritish Geological Survey, National Geosciences Data Centre,Keyworth, Nottingham, The possibility of landslipand the occurence of NG12 5GG. Thearchival data are held at the previouslandslips are considered both within the AberystwythOffice of the British Geological sectiononEngineering Geology and that on Survey andenquiries should be directed to The Summary of Geology. Activelandslip has been Regional Geologist for Wales, British Geological identifiedat some sitesand many apparently Survey, Bryn Llanfarian,EithynHall, inactive landslips were also mapped. Of the Aberystwyth, Dyfed SY23 4BY. bedrockformations, those containingweathered shale (e.g. the HalkynFormation) are the most susceptible to landslipping and of the superficial deposits, head is particularly prone. The bedrockThe geology superficialits and 4 Deeside(North Wales) ThematicGeological Mapping NOTES TO THE USER AND LIMITATIONS Notes to the user All National Grid references in thisreport lie This report and its constituent maps provide only within the 100 km square SJ. Grid references are general indications of ground conditions and must given to eithereight figures (accurate to within not be relied upon as a source of detailed 10 m), or sixfigures (accurate to within 100 m) information about specific areas, or as a for more extensive locations. substitute for site-investigations or ground Data used in preparing this report and associated surveys.Users must satisfy themselves, by maps are lodged at the Aberystwyth office of the seeking appropriate professional advice and BritishGeological Survey. enquiriesAny carrying out ground surveys and concerning these documents should be directed to site-investigations ifnecessary, that ground the Regional Geologist for Wales at that office. conditions are suitable for any particular land use or development. Boreholes andshafts registered with BGS are identified by a four elementcode (e.g. SJ 26 NE 112). Thefirst two elements referto therelevant 10 km National Grid square, the thirdelement to thequadrant of thatsquare and the fourth to the accession number. In this report boreholes and shafts are generally referred to only by the last three elements (e.g. 26 NE 112). Limitations Thisreport and its constituent maps have been produced by collation andinterpretation of, a9d interpolation from geological, geotechnical and related datafrom widea variety of sources. Details of the various sources of the data together with an evaluation of theirreliability are contained in the report. The maps provideonly a general description of thenature and extent of factorsrelevant to the planningof land use anddevelopment. The data on whichthey are based are notcomprehensive and their quality is variable, and the maps reflect the limitationsthe thatdata.of Localised or anomalous featuresand conditions may not be represented, andany boundaries shown are only approximate. No information made available after 3 1st December 1987 has been taken into account. For these reasons: Deeside (North Wales) Thematic Geological Mapping 5

Y:I 0 6 Deeside (NorthWales) ThematicGeological Mapping

Boundary of component Approximate eastern limit of area of National Grid 1 :10 000/1:10 560 -. .I..- outstanding naturalbeauty Sheet identified thus: eg SJ 27 NW ...... Boundary of component ...... Existingbuilt-up areas ------County grid 1 :10 560 ...... Sheet (Flintshire) identified thus : eg: 6NW ......

A Generalised position 'Greenof Barriers' ---- North- eastern limit of study area (Clwyd Structure Plan)

-0-0- Eastern limit of special landscape area v/&, Majorindustrial estates

-\--i Figure 2 Sketch-map showing the component 1:lO 000/10 560 sheets of the study area, the outlines of the earlier County Sheet Grid, and selected planning features Deeside (North Wales) Thematic Geological Mapping 7

INTRODUCTION framework. The data summarised in this report were obtained The aims of the project were essentially twofold. duringathree year contract, commissioned in 1. Toproduce a new set of geological maps at 1985 by theDepartment of theEnvironment on 1: 10 OOO/ 10 560 scale of the entire area, based on behalf of the Welsh Office. Funding for the work systematic a field survey and incorporating was sharedjointly by theDepartment of the borehole and subsurface data where available. Environmentand the British Geological Survey. The study area (Figure I), which is referred to in 2. To producea set of thematic element maps at this report as the Deeside area, is defined by the 1:25 000 scale and to collatevarious geotechnical followingOrdnance Survey (OS) National andother availableinformation reporta in Gridlines, andthe border between Wales and intended for use principally by plannersand England; developers. Thethematic maps delimit areas and sites of specific geological characteristics.The Eastern boundary SJ 3400 informationcontained on these maps is highly Western boundary SJ 1700 selective as it is not possible to reproduce all of Southern boundary SJ 6000 informationthe present on the new Northern boundary SJ 7800, but excluding the 1: 10 560 geological standardsatthe areasouth of . this OOO/lO reduced scale 1:25of 000. Furthermore,the boundarywhich lies quality of data on some of thethematic element within England. maps is very variable.For example, the available Thecomponent 1:lO 000 and 1:lO 560 maps are information for theextent of underground coal shown in Figure 2. seams was recorded over a period stretching from themiddle of thenineteenth century to recent The area occurs within that covered by Sheets 96 times andin some parts of thearea, no (Liverpool) and 108 (Flint) of theBritish information is extant. Geological Survey. It lies entirelywithin the county of Clwyd and includes several large towns, The use of this report includingFlint, Connah’s Quay, Mold, Buckley and Holywell. It must be stressed that the information provided on thethematic maps andinthe report is Objectives interpretive, of variable quality, and is distributed The reportprovidesThe updated geological unevenly. Consequently,the maps andreport informationwhich is needed for planningand should only be used in preliminary investigations. developmentpurposes inthe Deeside area,for Theycannot be considered as asubstitute for example in helping to rationalise between on-site investigation. Rather, they should be used developmentneeds and preventingthe potential as areference source providing aregional and sterilisation of valuablemineral resources which backgroundcontext to assist inthe interpretation areidentified. Other important factors include of detailedon-site observations. Furthermore, the informationrelevantground stability, to report should act as a guide to other more detailed geological hazardssuch as subsidenceand sources, e.g. Britishthe Geological Survey landslips, geotechnicalcharacteristics and archives of non-confidential boreholes andother groundwater. including,data, most importantly, the 1: 10 10 560 geological standards,open-file Theethos of thereport is to provide the OOO/ reports, and the original field-slips and annotated geological information in a readily comprehensible air photographsair which arethefundamental form. and assumes thereader may have little sources which much of thereport is based. It geological or geotechnical background knowledge. on is strongly recommended that the maps and report Hence technicaljargon is kept to the minimum. shouldnot be used in isolation of oneanother. Since, however, some technical language is Each map has only a limited des-criptive key and a necessary, a glossary of terms is included to assist fullerdetailed description with relevant provisos thereader. Theform of presentationadopted is is contained in the report. inline with the recent emphasis placed by the Department of theEnvironment on producing In areas of particularlydetailed information, e.g. applied geological maps as a way of better the distribution of shafts on HalkynMountain in communicatingresults than traditional reports thenorthwest of thearea, some textfigures at a constrained by a more geologically based larger scale areincluded inthe report. Some 8 Deeside (NorthWales) ThematicGeological Mapping information, most notablywith respect to sections of rockexamined under the high-power geotechnical data, was found to be distributed too microscope, were carried out by Dr. N J Riley of unevenly to warrantproducing a thematic map. theKeyworth Office of BGS. Theidentified Such information has been incorporatedin the fossils were used in correlating between exposures. report in tabulated and graphical form. Acomplete set of ‘geological standards’ was then produced.These are fair copies of the base maps Data sources used in the report at 1:lO OOO/lO 560 scale. 1. BritishGeological Survey (BGS) archival maps Eachmapdelineates bothlithological and anddata. Two previous surveys of thearea had structuralvariations in the bedrock geology and been carriedout at 1:lO 560 scale, aprimary the nature and distribution of superficial deposits survey by Strahan and De Rance (1879-85) and a (drift). In addition, details relating to mining and revision of the Coal Measures by Wedd, King, quarryingactivities are recorded andthe sites of Thomas and Lamplugh (1910- 13). The field-slips selected non-confidential boreholes plotted.Each relating to these twosurveys are held atthe base map (see AppendixA for details) has a AberystwythOffice of BGS. Descriptive memoirs generalised verticalsectionwith general of bothsurveys were produced (Strahan, 1890; descriptions of constitutentthe geological Wedd andKing, 1924) and maps published at formations.To accompany each base map,an 1:63360 scale. In addition, maps of thecoal open-file . report has been produced. These measure sequences werepublished at 1:lO 560 reports give details of all significant exposures of scale as resulta of the revision survey.The bedrocksuperficialand deposits including metalliferousdeposits of thearea were described measured thicknesses anddescriptions of the in a ‘Mineral Resources Memoir’ by Smith (1 921). various lithologies. They also give details of Extensivenon-confidential confidentialand selected non-confidential boreholes andshaft borehole recordswere held prior to the present sections. projectat the Aberystwyth Office ofBGS, as 3. Information was sought from alarge number were some geotechnicalreports, and plans and of holders of geological data. The largest single cross-sections relating to metalliferous mining. source of informationobtained was the database 2. Informationfrom the new geological field held by British Coal. Borehole dataobtained survey of theentire contract area,carried out from theOpencast Executive was used to derive between June 1985 and August 1987. The informationprimarythebut data remains observationsmade during surveythe were confidential. Seam plan information was collated recorded directly on to 1: 10 OOO/ 10 560 field-slips from the Coal Commission plans, and other plans butin areas particularly of intensivemining held by British Coal, StaffordshireHouse, Berry activity,information was recordedinitially on Hill Road,Stoke-on-Trent, ST4 2NH. A black photographswhiteair and (scale synthesis of this data is held on maps at 1: 10 560 approximately 1: 10 000) and was transferred scale at Aberystwyth Office of BGS. Opencast subsequently to the base maps. Theair abandonment plans were also obtained. photographswere obtained from Clwyd County Site-investigationinformation for civil Council, who hold a set of photographs providing engineering projects comprising borehole data and completestereoscopic coverage of the area. trialpits,with in many cases details of Standard BGS mappingtechniques were used engineeringproperties, and in some instancesfull duringthe field survey. These include systematic geotechnical and other reports were obtained from examination of all exposures of rock. Detailed many bodies, includingthe Welsh Office, Clwyd descriptionsand measured sections were recorded CountyCouncil, Alyn and Deeside District where appropriate.Thelarger working and Council, Delyn District Council, Glyndwr District disused quarriesin limestone providedthe most Council, the Welsh Development Agency anda detailed sections, allowing close correlation to be number of geotechnicalconsultants. Most of performed. Most topographicfeatures greater these boreholes were carriedout using shell and thanapproximately 1 metrein elevation were auger methods andare less than 25 min depth, systematically recorded to assist interpretationin and many are restricted to the unconsolidated areas of limitedrock exposures. In mapping the deposits. Thedistribution of borehole sites is superficialdeposits, hand augers (1.4 mlength) very uneven,with particular concentrations along were used to provethenature of subsoil. the A55 andother road improvement schemes. Identificationsboth of fossils recognised in the Accessto borehole core was provided byWimpey fieldand of microfossils, visible only in thin Deeside (North Wales) Thematic Geological Mapping 9

P.L.C. Six appendices are presented. These are: 4. During 1986, 12 boreholes were drilled, as part A. A list BGSof geological standards, of the project, by theshell and augermethod in open-fileand palaeontological reports order to provesand and gravel resources in the produced for the area. north of the area. The logs of the boreholes, B. Geotechnical tests quotedin the database, associated geotechnical data and particle size data andtheir applications. of thedeposits are contained inAppendix F. C. A list of boreholes held inthe BGS Togetherwithothernon-confidential and archives. Where confidential,only the BGS confidential boreholes, records from reference number and the source of the approximately 4,500 boreholes were considered borehole are provided. Where during the project. non-confidential, the BGS reference number, its National Grid Reference and, where known, 5. Variouspublications relevant to thearea are date of sinking,surface level, drift available inthe scientific literature. These deal (superficialdeposits) thickness, borehole particularly with aspects of the stratigraphy of the depthand availability of geotechnicaldata CarboniferousLimestone sequence and with the are given. natureand interpretation of superficialdeposits D. A list of shaftssunk for coalwith the withinthe area. These arereferred towhere BGS archivalreference number, the British appropriatewithin the report and full details are Coal referencenumber, its National Grid given inthe reference list. These referencesare Reference (6 or 8 figure)and, whereknown, available in the libraries of the British Geological the thickness of drift (superficial deposits) and Survey at Aberystwyth and Keyworth.Other its depth. usefulreference centres are: Londonthe A selective list of shaftsand adits identified InformationOffice, British Geological Survey, E. as being open at surface, at the time of ,Geological Museum,Exhibition Road, London survey. SW7 2DE; theDepartment of Geology, Jane Borehole logs and particle size dataare HerdmanLaboratories, University of Liverpool, F. given for those boreholes carried out as part of P.O. Box 47, Liverpool; andfor historical the project. informationwithreference to mining and quarrying,the Clwyd RecordsOffice, Clwyd GEOGRAPHICAL AND PLANNING County Council, . BACKGROUND Constituent parts of the results Geographical background Seven thematicelement maps are includedwith Thestudy area (approximately 265 km2) lies thereport. These are: entirelywithin the county of Clwyd. Its regional context is demonstrated by Figure 1. The 1. Bedrock Geology component OS 1:lO 000/10 560 sheets of the study 2. Superficial (Unconsolidated) deposits areaare shown inFigure 2, togetherwith the 3. Boreholes, Rockhead and thickness of outlines of the former 1:lO 560 County Sheet grid Superficial deposits which was used as thetopographical base for 4. Mining activities; Coal/Metalliferous previous geological surveys of thearea. Much of 5. Resources (Bedrock) - except thearchival material used in the report isalso Coal/Metalliferous recordedCountytheon Sheet base. The 6. Resources - Sand and Gravel generalised topography,drainage pattern, and 7. Hydrogeology and Water Supply major towns are shown in Figure 3. Full descriptions of each of the thematic maps are The economy of thearea is mixed,combining containedin the report, and anoutline of the agricultureruralin districts with industry geological history is given. Asection is devoted principallyaround thelarger towns. Mineral to engineering geology. It deals withthe extractive industries are a major component of the geotechnicalcharacteristics of bedrockthe local economy, providingaggregate both for local formations and superficial deposits and highlights needs andfor majorthe conurbations of associated problems. Representativedataare , GreaterManchester and elsewhere presented in tabulated and graphical form. (see ‘Mineral Working in Clwyd’, 1982). There has been arapid evolution in recent years from traditional heavy industry towards those of the IO Deeside (North Wales) ThematicGeological Mapping

Contours in metres '''\ above 0.D. Principal streams h and rivers ...... m.3~4 Mainly built-up ...... +.:::m.:2x> areas

0 2 -km

Figure 3 Topography, drainage and chief towns of the study area Deeside (North Wales) Thematic Geological Mapping I I new technologies, andurban development and clay-filled hollows occurs,particularly along the redevelopmentreflect these relatedand Alyn Riverand to the southwest of demographic changes. [SJ 245 6851. The area reaches its highest point (441 m) in the The main towns of thearea are Connah’s Quay, southwest, on the steep flanks of in Flint, Holywell, Mold and Buckley, with most theClwydian Hills. These hills areseparated industryconcentrated around these centres. New fromthe north-northeast trending escarpment of industrialparks atGreenfield, Flint, Shottonand the Carboniferous Limestone by the valleys of the Mold are the focal points of new, high-technology Alynand Wheeler rivers. The roughpasture of industries. The main extractiveindustry is theClwydian Hills contrastsmarkedly with the limestone quarrying,mainly for aggregatebut ruralaspect of themore fertile limestone terrain. with some production for cement,industrial and The AlynRiverThebreaches limestone the agricultural use. Production is currentlyfrom escarpment west of [SJ 203 6681. seven sites. Sand andgravel is also extracted at There is asimilar east-west breach atHendre two sites, for aggregate purposes; mouldingsand [SJ 195 6771. FromRhydymwyn, the Alyn trends forthe steel industry and other purposes is generally southwards,past Mold, eventually to produced in small quantitiesat one site. jointhe River Dee southeast of the study area. Following theclosure of the last collieryin the The Dee itself flows to the northwest, across the areain the 19303, no coal extraction is extant, northeast part of thearea, its wide flood-plain butopencast production remains a possibility for east of Connah’s Quay giving way to thebroad thefuture. Fireclay quarrying for thebrickclay Dee Estuary northwest of Connah’s Quay. industry is now limited to onesite at Buckley. Chertand calcspar have been workedin the The limestone escarpment, with west-facing crags recent past. andmore gentle slopes to the east, extendsthe length of thestudy area from south of Publicwater supply is provided from several [SJ 205 6281 towards Holywell inthe north. abstractions within the study area, but most of the Considerable exposure of bedrock on the westerly water used comes fromsurface and groundwater aspect of the escarpmentcontrasts with the sourcesoutside the area. The Halkyn-Wolywell typically sloping grassland to the east. Cattleand mine drainagescheme has provided animportant sheep farming predominatein this part of the source of water for industrial use. area. Thelimestone terrain includes the common landarea of HalkynMountain which rises to a Planning background maximum height of 294 m. Thisrough The Deeside area is typical of many areas in pasturelandhas been extensively mined for lead Britainexperiencing the uneasy economic andthe resulting minetips have disrupted local transition associated with the decline in traditional drainage and sterilised the soil. heavy industriesand their replacement by an North to northwesttrending escarpment features expandingservice sector and newlight and of progressively diminishedelevation occur high-technologyindustries.Unemployment towards theeast of the limestone escarpment. higherthan the national average has been the Thispattern of featuresexerts the main control consequence of this change and the importance of on the drainage system in the north, with streams redevelopment is clear.However, two significant hugging the bases of the westerly to parts of the local economy, namely agriculture south-westerlyfacing escarpments. Other streams and themineral extractive industry (limestone, drain the gentle back-slopes of the escarpment. sand and gravel, and opencasted coal) are likely to continue to play an important role. This fact was Much of theeastern part of the area, including clearly recognised inthe ‘Clwyd CountyStructure - the exposed and concealed coalfield, is of low elevation m) with minor undulations, but is Plan’ (1 982), with policy statements recognising (450 theimportance of rationalequilibrium between deeplydissected by streams. Clayey soils are development pressures, conservingagricultural typical andthe agriculture is mixed dairyand productivity,environmental protection and the cerealproduction. Near the Dee Estuary,the efficient use of availablemineral resources. Thus groundfalls away rapidly and many deep it is statedthat ‘... there will be stronga north-east trending river dissections occur. A flat presumption against the use of agricultural land of estuarinealluvial strip extends along the coastal margin. Moundytopography characteristic of grades I, I1 and 111 for non-agricultural purposes.’ With regard to the development and control of sand andgravel deposits, with small peatand I2 Deeside (North Wales) ThematicGeological Mapping mineral working, the relevant policy indicates that affecting development costs, project duration, and ‘... close regard will be had to the economic need (under the provisions of the Health and Safety at forthe mineral and to the significance of the Work Act, 1974) thesafety of schemes. Hence, proposal for local employment. All proposals for thegeotechnical characteristics of deposits likely mineral working will be considered in the light of: tobe encountered during developments must be a. the demand for and the quality of the product; reviewed,and the impact of geologically related b. the availability of alternatives; c. local, problems minimised. regional and national needs and reserves; d. their likely effect on any town or village.’ GEOLOGICAL INFORMATION RELEVANT TO PLANNING Criteria for the consideration of mineral working proposals include agricultural land quality, nature Themain areas in which geological conditions conservationinterests (e.g. Sites of Special affect land use planning are: ScientificInterest), the impacton the landscape, Mineral extraction and resources landdrainage and water supply, highways and Engineering geology transportation,and the scope for restorationand Water resources rehabilitation. It is furtherintended that, to preventthe sterilisation of mineral resources, ‘mineral -reserves of special economic value Minerai extraction andresources . regionally or nationally will be safeguarded from Giventhe fact that largequantities of aggregate otherdevelopment, either on site or nearby.’ The (limestone, andsand and gravel) are ‘exported‘ Clwyd CountyPlanning Authority are currently from theregion (see North Wales Working Party preparinganalteration to thestructure plan on Aggregates, Report 198 1; Mineral Working in including an expanded set of policy guidelines for Clwyd, 1982) particularlyto northwest England, theextraction of mineral resources. The Local pressures for increasingdevelopment of the DistrictCouncils also define policies for extractive industries arise from external as well as developmentcontrol through local plans, while local demands. The provision of thematic maps further constraintsapply underthe Control of provides animportant data source with regard to Pollution Act, 1974, and the Health and Safety at mineralworking. They delimit the various finite Work Act, 1974. bedrock andsuperficial resources and provide informationtheonthickness variations and Within the Deeside area, the ClwydCounty quality of the deposits. Suchinformation also Structure Plan citesseveral areas around and assists in the efficient siting of plant in order to separatingsettlements, known ‘Green Barriers’ as avoid sterilising valuable resources has been the (see Figure 2), for which there would be a strong as case inthe area in previous years (e.g. at the presumptionagainst development that would Brookhill Brickworks Fireclay pits [SJ 279 6561). affecttheir open character. The structure plan definesan extensive Special Landscape Area for Thefollowing comments relate to specific theprotection of those parts of thecounty resources: possessing the ‘highest landscape quality’. The easternpart of thisfalls within the study area. Limestone Also, a smaller tract of country was designated by The extensive limestone outcrop in the west of the theSecretary of Statein 1985 theClwydian as area is avaluable resource for aggregate,cement Hills Area of OutstandingNatural Beauty. In andfor industrial and agricultural purposes. The additionLoggerheadsthe Country Park outcrop has been subdividedintoseveral [SJ 199 6281is designated a Site of Special as formations(units)distinctwith resource ScientificInterest (SI) (Figure 6), arethe as characteristics (e.g. purity,limestone to shale [SJ 195 6571 north of and ratio). Limestoneextraction is currentlythe most part of the Estuary. Dee importantextractive industry the in area. With respect to water resources, theControl of Aggregate is produced at six sites andone other Pollution Act 1974 legislates thatgroundwater be quarryproduces limestone for cement making. protected from pollution.Hence, protection of Limestone has been extractedfrom numerous the major aquifers of the area from, for example, other smaller sites in the past (see Thematic industrialand toxic waste disposal is higha Element,Map 5). The presence of the limestone priorityin terms of planningand development. resource is asignificant factor in planning, and Consideration also has to be given to factors while scope exists for deepeningexisting quarries Deeside (North Wales) Thematic Geological Mapping 13 withoutmajor drainage problems, future demand limitedsuperficialand overburden often may well give rise to calls for expanding existing substantial, specific areas of opencast potential are quarriesor for developing new ones. not readilypredicted, andstrategic planning is Consequently,planners and developers(quarry hampered. Theimpact of former coal mining companies) will need aninformation base from activity (see Thematic Element, Map 4) is of more which to identify potentiallysuitable areas for practicalconcern, e.g. in knowing areas of future extraction. The limestone is asignificant underground workings, indicatingwhether more source of groundwater, having provided water for than one seam has been worked at a site and thus industrial use via the Halkyn-Holywell Drainage compounding possible subsidence problems, the Scheme and, as such,requires planning position of shaftsand the distribution of waste protection. tips and backfilled opencast sites.

Sand and Gravel Fireclay Significantsand and gravel deposits occur in Extraction of fireclay for thebrick industry was severalparts of the area. Currently, two sites are formerlyimportant in the Buckley areabut is exploited for aggregateproduction, and deposits extantat only onesite. Resource protection and have been worked at several smaller sites inthe future extraction are not likely to be of immediate past. There is increasingdemand for sand and concern but future demands for fireclay cannot be gravelnationally (Mineral Working in Clwyd, predicted.Information regarding former quarries, 1982) andthis is likelyto persist. As thesand andrelated backfill deposits (see Thematic andgravel deposits are relativelythin (x40 m), Element,Map 5) will however be of value in theirextraction in significant volume necessitates assessing other developments in their vicinity. pits of large areal dimensions which are relatively ephemeralcompared to those associated with Chert bedrockquarrying. The deposits tend to occurin Chert was formerly quarried for aggregate and for areas of highergrades of agriculturalland and use inthe glassmaking andsilica brick industry. substantialsites may needto be identified for Extraction was locally considerable,but none is future extraction.Additionally, planners will extant. As fireclaywithdeposits, the have to ensure that sterilisation by development of consequences of extractionare of more obvious thiscomparatively limited and valuable resource concern to plannerthe than is resource (see ThematicElement, Map 6) is avoidedwhere conservation. However, possible future usesof possible. It should be notedthat sand and gravel thisresource, which it should be stressed is deposits oftenoccur as moundy topographic relatively uncommon nationally,should not be features and their removal alters the landscape in ignored. a way which is hard to restore to the original form.Potential resources, includingconcealed Sandstone deposits, wereidentified in the southeast of the area by theIndustrial Minerals Assessment Unit Numerous small quarriesin sandstoneoccur but of the British Geological Survey (Ball and Adlam, there is activeextraction onlyat one site. 1982) andfurther information is given inthis Sandstones of differing resource charactersare report (see also Appendix F). Thedeposits are identifiedin the report (see ThematicElement, very heterogeneousand vary greatlyin thickness. Map 5). These resources arescattered widely Consequently the quality of the resource can only across thearea and most are of little economic be proved by site-specific investigations. importance.Thus,resource sterilisation of sandstone is unlikely to be majora planning Coal consideration.The sole site of extraction is for sand from theKinnerton Sandstone of Triassic Coal mining by shallow anddeep methods (pillar age. Its outcrop is limited by thicksuperficial and stall or longwall) and more recently by deposits and is unlikely to be a significant factor opencasting has been a major industry over. much in planning decisions. of the central and eastern parts of the area in past years. No mining or opencasting is extant, though Lead, zinc and copper ores opencasting may occurin the future. Economic considerations suggest thatfuture extraction is Considerable mining of lead, zinc and copper ore likely to be from limited opencast sites only. As took place largely inthe second half of the exposure of the coal measure sequence is very nineteenthcentury but none is extant. Although 14 Deeside(North Wales) Thematic Geological Mapping resources stillexist, particularly atdepth, their For planning and development purposes, the extraction is uneconomic in present or foreseeable deposits of the study area can be divided into five terms due to drainage problems andthe principal engineering groups: unpredictablenature and quality of the resource. 1. Rock Thisaspect is ther-efore of littleconcern to 2. Overconsolidated cohesive soils (clays and silts) planners. As withcoal mining, the results of this 3. Dense non-cohesive soils (sands and gravels) intensivemining, which is restricted to the west 4. Heterogeneous deposits (mainly head) of area,theprovide the most important 5. Normally consolidated cohesive soils (clays and considerations. Most of the multitudinousshafts silts) and non-cohesive soils (sands and gravels) have not been capped and many present danger to membersof thepublic as well as potential Rock problems to development schemes. As increasing leisure use is made of thelimestone terrains (e.g. Whilst the rock(bedrock), as a whole, often thecommon land of HalkynMountain and provides a suitablefoundation for most Loggerheads Country Park) consideration must be light-weight structures, this is not always the case. given toreducing these hazards. It was noticed Themudstones and shales particular,in are thatit is commonlythe practice for farmersto weatheredto varying degrees and depths. This attempt to reclaimland affected by trialpits and weathering to claya soil is likely to reduce shafts by bulldozingthe areas flat.This allowable bearing pressures. Weathering is greater techniqueserves only as atemporary, cosmetic where drift cover isless. As ageneral rule, piles treatment of the problem and arguably may need to be takenthrough the worst of the increasepotential hazards in the long term. The weathered zone intofresh or slightly weathered distribution of shafts,whichto particular rock. Landslipsoccur within theweathered attention was givenduring the field survey, is mudstone and shaleand, consequently, careful given on Thematic Element, Map 4; more detailed investigation of siteson weathered mudstone and maps of shkfts and trial pits on Halkyn Mountain shale slopes, and especially those steeperthan andat Loggerheads are givenwithin the report about 7', must be made to confirmtheir (Figures 5a, 5b, and 6). long-termstability. The weathered mudstones and shales are generally unsuitable as fill and care Peat is neededwhen constructing cuttings to reduce their exposure to wetting. Minorextraction inis progress at one site. Deposits are very localised, scattered and Theother rock types, limestones, sandstonesand small-scale and as such, do notconstitute an chertsgenerally provide good foundationsfor important resource. most light-weightstructures. However, potential hazards are presentand need tobe consideredin Calcspar anyinvestigation. These include infilled or open cavitiesthein limestones, unevenrockhead Small-scale extraction has untilrecently been in surfacewith open andinfilled joints and progress at one site. Although relatively common, sandstoneweathered to dense a sand. The thisresource is rarelysufficient to warrant its limestones aregenerally strong but thisstrength economic extractionand is notsignificanta maybe reduced en masse by interbedded planning consideration. mudstone or shale bands. Ease of excavationin the rock will also varywith the degree of Engineering Geology weathering. Thereport synthesises and presents available geotechnical data relevant to planningand Overconsolidated Cohesive Soils development.foundationincludeThese The tills that make upthe overconsolidated soils characteristics, ground stability including landslip, are widespread. Theyvary vertically fromsoft, the ease of anddurability of excavations, the weak materials at thetop of theweathered zone, suitability of availabledeposits as afill material to stiff to hard materials at depth. They are very and groundwater problems. variabletheirin foundation conditions. They generally providesatisfactorya foundation for light-weight structures though lateral variation on a site-scale may make differential settlementsa possibility. Deeside (North Wales) Thematic Geological Mapping 15

gravel layers may providebetter foundation Granular materials in the till are prone to running conditions(though the nature of thedeposits or pipingconditions or highwater flows and underlying the gravel must determined).be hence cuttings may need good drainage. Clays in Conversely, peat horizons inthe alluvium or the till may softenrapidly on wettingleading to organic clays inthe estuarine alluvium may also boggy conditions and unstable pit or trench walls. be found,both of which are unsuitable for any The till is generally suitable as a fill material. As foundation. a whole, it needscarefulsite-specific investigation determine to geotechnicalits Hydrostatic pressures inthe estuarine alluvium variability in three dimensions. may fluctuate because of the tidesand this will affect bearing capacities. Groundwatercontrol Dense Non-Cohesive Soils for excavations, togetherwithshoring are essential. In the estuary, piles founded in denser, Theseinclude the widespread glacial sandsand coarser deposits at depth will usually be required, gravels and some of thedeeper and coarser thoughskin friction values in thenear surface estuarinealluvium. The glacial deposits aremore deposits will be low. variable, often containing clayey and silty horizons. Where dense or very dense, the deposits The non-cohesive loose depositshave higher provide adequatean foundation for most bearingcapacities than the cohesive soils inthis purposes. Forestuarinethe alluvial sands, groupbut they are often variable lithologically however,piling to some depth may be necessary leading to possible differential settlements. to find a suitable bearing horizon. Perchedwater-tables and high permeabilities in these deposits mean thatgroundwater control for Excavations need supportand running conditions excavationsand cuttings will be necessary. They are likely, particularly in theestuarine alluvial can be used as afill material only where clay is sands, so thatde-watering may be required. absent. Lithological andgeotechnical variation on Cuttingsthrough these deposits need adequate a site scale will need careful investigation. drainage and highwater pressures may be found in sands or gravels overlain by less permeable Groundwater clays, leadingto possible heaving or sagging on excavation. Fewgeotechnical problems areanticipated from groundwatersulphate contents or pH values for Heterogeneous Deposits (mainly Head) anydeposit except where the groundwater has been contaminated by waterdraining through This deposit is very heterogeneous in composition mine waste tips. Forsites in the vicinity of such and is foundin variable thicknesses (frequently tipsgroundwater quality should be carefully less than1 m) on hillslopes andin valleys. Shear monitored to determinewhether higher quality planes within it are a possibility and consequently is required and whethersteelwork needs there is a risk of landslip. Thus, where slopes are protection. steeper than about 7O, careful site assessment must be made. Water Resources Where head is thin, it is likely to be stripped off Groundwater is generally less vulnerable to thesite prior toconstruction. In otherareas pollution thansurface sources because of the however piled foundations may be necessary with filtering and attenuating effects of the unsaturated piles founded beneaththe head. The zone aboveaquifer.the Consequently it heterogeneity of thedeposit makes generalisation commonly receives littletreatment before being difficult. pumpedinto supply. This means thatit is importantthataquifers areprotected from Normally Consolidated Cohesive and Loose potential pollutants. Thereare two main sources Non-Cohesive Soils of pollution,point and diffuse. Point sources The cohesive soils are usually unsuitable as a includelandfills and other waste disposal sites foundation for evenlight-weight, single-storey such as sewage treatment works, and storage tanks structures,with large settlements possible even at for silage, fuels,industrial solvents andother lowloads. The depositscan be variablein chemicals. Thereare several landfill sites that composition leading to possible differential have in the past or currently accept household and settlement.Accordingly, foundations or piles may industrial waste. However,generally they need to be takenthrough the deposit. Occasional representlittle risk to groundwaterquality 16 Deeside(North Wales) Thematic Geological Mapping because of thepresence of impermeabledrift deposits.Storage tanks, particularly where poorly constructedor in bad repair, can represent a serious risk to groundwater quality. Diffusesources of pollutionare nitrates, applied to theground inthe form of fertiliser,and biocides (particularly herbicides); both are widely used inagriculture. As much of thearea under considerationis agricultural these are a risk to groundwaterquality. However, the risk islow with respect to the major aquifer in the area, the KinnertonSandstone Formation, because isit overlain by considerablethicknesses of unconsolidateddeposits of low permeability.The CarboniferousLimestone which occurs atthe surface over large areas is at greater risk. Deeside (North Wales) Thematic Geological Mapping 17 GEOLOGICAL SEQUENCE The bedrock formations, in stratigraphic (age) order, and superficial deposits recognised in the area are: SUPERFICIAL (UNCONSOLIDATED) DEPOSITS Recent Backfill Made ground Alluvium Estuarine Alluvium Alluvial Terrace Alluvial Fan Landslip Quaternary Landslip Peat Head Sand and Gravel Till (Boulder Clay) BEDROCK Thickness (m) ?Tertiary (Solution-pipe infills). Permo-Triassic Kinnerton Sandstone Formation up to 300 Carboniferous (Westphalian) Ruabon Marl up to 120 Buckley Formation up to 250 Productive Coal Measures (Westphalian C) 0 - 150 Hollin Rock 10 - 70 (Westphalian B) 100 - 150 Drowseil (or Massy) coal 0 - 1.21 Powell (or Bind) coal 0 - 1.07 Hollin coal 0.7 - 2.75 Crank coal 0 - 0.96 Quaker (or Brassey) coal 0 - 1.19 Black Bed (or Rough) coal 0 - 1.11 Main coal 1.8 - 4.5 Lower Bench coal 0 - 0.76 Crown (or Diamond) coal 0 - 1.83 (Westphalian A) 160 - 230 Upper Red (or King) coal 0.35 - 1.8 Lower Red (or Cannel) coal 0.3 - 1.0 Stone (or Wall and Bench) coal 0.15 - 4.14 Nine Foot Rider coal 0 - 3.0 Nine Foot coal 0 - 2.87 Nant coal 0.48 - 1.93 Ruabon Yard (or Yard) coal 0 - 1.68 Premier coal 0.45 - 2.13 Half Yard (or Half Yard) coal 0.4 - 1.3 Chwarelau (or Little) coal 0 - 0.88 (Namurian) (=Millstone Grit Series) Halkyn Formation 250 - 350 Sandstone 0 - 150 ‘Cefn-y-Fedw’ Sandstone 0 - 80 ‘Pentre’ Cherts 0 - 150 Carboniferous Limestone (Dinantian) Formation . 0 - 170 Cefn Mawr Limestone 50 - 120 ‘Main’ Shale 0-4 ‘Thick’ Shale 0 - 3.5 Loggerheads Limestone c 170 Leete Limestone 75 Llanarmon Limestone c 150 Llwyn-y-fran Sandstone 0 - 20 Foe1 Formation c 20 ‘Basement beds’ 0 - 5(?) Silurian (Ludlow) Elwy Group up to 350 18 Deeside (NorthWales) ThematicGeological Mapping

DESCRIPTION OF THEMATIC GEOLOGICAL of distinctive geological characteristics (e.g. MAPS similarcomposition, grain-size, sedimentary structures,persistent association of beds of Notes about the topographic base different rocktype).Specific lithologies can be recognised withinformationa (e.g. sandstones, The topographic base used (scale 1:25 000) was coal seams) and named accordingly as a ‘member’. compiled by the Welsh Office,. As the Theseneed only be of local distribution. Where constituentOrdnance Survey (OS) 1:25 000 base severalformations have generala relationship, maps are of differing ages, changes in topographic they can be amalgamated to form a ‘group’. detail (e.g. housing, quarryoutlines) occur across some grid boundaries. In compilation, some The linework shown on the map is based on that imprecision pf thegrid alignment has occurred producedduring therecent 1:lO OOO/lO 560 field across these same grid boundaries. survey. Some simplification has proved necessary in reducing to 1:25 000 scale. In particular,the Several amendments have been made to the OS density of faults (e.g. inthe vicinity of Halkyn base. To inspectionaid of the geological Mountain inthe NW) has been greatlyreduced, informationadded, many of thefield boundaries and in some formations, most notably the Minera were removed. Furthermore,topographic Formation,the closely-spaced individual contoursarenotrepresented, although spot sandstones have been generalised as single packets, heights (in feet N of Grid Line 70 and W of Grid whereas in other instances, minor sandstones have Line 20, in metres elsewhere) are given. been removedaltogether where geologically The proposed lines of the improvements reasonable to do so. moreFordetailed were added by the Welsh Office.The routes information, planners and developers must consult shown varyslightly from those recently theavailable British Geological Survey (BGS) constructed,particularly in vicinitythe of geological maps andopen-file reports (see Holywell [SJ 1840 74781. This isof importance Appendix A) and BGS archival maps, field-slips whereembankment (made ground) has been andannotated aerial photographs held in the mapped, andin thisarea it is shown in its Aberystwyth Office of the BGS. accurateposition and is thusslightly offset from The bedrock succession of the area is given in the shown. the route of the A55 as form of a generalised vertical section. This shows thestratigraphic order of theformations, their List of Thematic Elements thickness variations (approximately to scale) across 1.Bedrock Geology the area and general relationships with underlying 2.Superficial (Unconsolidated) deposits andoverlying formations (i.e. normalcontact, 3.Boreholes, Rockheadand thickness of lateralequivalence unconformity).or Brief Superficial deposits descriptions of eachformation and member, 4.Mining activities; Coal/Metalliferous including age, rocktype,lateral and vertical 5.Resources (Bedrock) - except variations, andinterpretation of mode and Coal/Metalliferous environment of deposition are giventhein 6.Resources - Sand and Gravel Summary of Geology (see below). The 7.Hydrogeology and Water Supply cross-section (withvertical exaggeration relative to horizontal scale of x 2) is aninterpretation, Thematic Element, Map 1 - Bedrock Geology based availableon surface information and relevant borehole data, of thenature of bedrock The map depicts the distribution at the surface of atdepth along theline of sectionshown on the all of themajor bedrock formations, with map. The line of cross-section was chosen to best importantsubdivisions where identified. It makes illustrate the overall structure of the area. no attempt to portraythe vertical variations of bedrock,other than in the generalised vertical This map should be used inconjunction with section,and the cross-section appended to the ThematicElement, Map 2 - Superficial map face. A simplified geological map is (Unconsolidated)deposits, as theaccuracy and presented in Figure 4. certainty of thelinework depends to a large degree on theavailability of informationfrom The‘formation’ is thefundamental level of exposures of bedrock, and thethickness of the subdivision of a sequence of rocks and refers to a superficialdeposits (drift). Thus in areas of little body of strata which is recognisable and mappable or no drift, a lesser degree of interpretation is over large areas. Theformation comprises strata

20 Deeside(North Wales) Thematic Geological Mapping necessary.However, inmapping the coalfield, therefore very variable in grain-size, clast content considerable information is available, despite thick and fabric. drift cover,from boreholes,previous mining and Themap shows only the variation of surface opencasting.Therefore, in some areas, the deposits(i.e. within 1 metre of surface)and position of coal seams andfaults is well makes no attemptto showvariations with depth. constrained. Althoughthe deposit indicated on the map may Selected datatheorientationon of strata be considerablythicker than 1 metreand perhaps (direction and amount of dip from the horizontal) the only deposit overlying bedrock at a given site, aregiven. Faults arediscontinuities thein it is equallylikely thatthere may be many bedrock and mayin additionoffsettingto differenttypes of deposits.Therefore, borehole geological boundaries,coincide with changes datamust be consulted (see ThematicElement, within the formations. Most faults in the area are Mapand3 Appendix C). Limited information steep (within 20' of vertical). No attempt is made regarding thickness variations, mainly of sand and however to indicatethe variation of steepness graveldeposits, is givenon Thematic Element, (otherthan in the cross-section). Few faults are Map 6 Appendixandin F, andfurther ever seen in exposure other than in the mines and information in the Summary of Geology. quarriesand most, therefore, are inferred, and Depositsgenerally less than 1 metrethick are not theirposition subject to inaccuracy.The relative shown.Areas shown as bedrock, especiallythe downthrow of faults is shown,but not the limestone terrain, mayhave extensive veneers of amount. drift (usuallyhead). It may locallyexceed 1 metrein thickness, but such areas are too patchy Thematic Element, Map 2 - Superficial to show. Thindrift veneersmay, however, be a (Unconsolidated) deposits very importantfactor when considering local Thismap shows the distribution at surface of all groundstability (see sectionEngineeringon superficial(unconsolidated) deposits. The general Geology). term drift is applied to theunconsolidated, In addition to thedistribution of thedeposits, superficialdeposits of Quaternaryage, and these rockheadcontours are shown. For adescription are largely glacial in origin or are related in some of these, see the description of Thematic Element, way toglaciation. Localised peat and clay-filled Map 3, where the rockhead contours are repeated. depressions related to the deglaciation, and known as kettle-holes,are symbolised.Deposits which Thecategories of superficial(unconsolidated) have formedrecently, or are actively forming by deposits are briefly reviewed below. natural processes are also shown,together with man-madedeposits (made ground and backfill). Made Ground Themapdisplays landslip of various ages Areas of made groundare related tomining (Quaternary to Recent),and foundered ground (metalliferouscoal),quarryingand [e.g. and swallow holes (symbolised individually) in the SJ 198 703, SJ 188 7241, landdevelopment and CarboniferousLimestone terrain, which may road and railwayembankments. The largest areas containclays and silts as old as Tertiary.The of made groundare thosealong thenortheast swallow holes are dissolutionpipes in the coast, related to industrial development (especially limestone; they may be vertical or inclined. on the site of the Shotton Steelworks [SJ 31, 701, at The mapshavebeen simplified fromthe Flint [SJ 245 7351, Connah'sQuay [SJ 28 711, 1:lO 000/10 560 geologicalmaps produced during [SJ 215 7601, and Greenfield [SJ 198 7771). the recent survey(1985-87).recent theBorehole The various forms of madeground are not information was used to aid interpretation. distinguished,but forfurther information see ThematicElement, Map (Mining 4 activities; Thesuperficial and other unconsolidateddeposits Coal/Metalliferous),Map 5 (Resources(Bedrock) arecategorised according to two factors, a)the - exceptCoal/Metalliferous) Mapand 6 process bywhich they were formed, and b) the (Resources - Sand and Gravel). composition of thedeposit. The former includes landslip, made ground, backfill, foundered ground Mining waste tipsrelated to metalliferous mining andthe various forms of alluvium.The latter generallycomprise calcite vein material andthe includestill (boulder clay), sand and gravel and local country rock, principally limestone and some peat. Blown sandinvolves both factors. Those chert. Coaltipsusually comprise mudstone, categorisedsolely according to process are siltstone andsandstone debris. Made ground Deeside (North Wales) Thematic Geological Mapping 21 related to limestone quarrying generally comprises Estuarine Alluvium calareous mudstone andmuddy limestone, while thatrelated to sand and gravel extraction usually Areas of alluvial sedimentare currently being consists of fine-grained sand, silt and mud. deposited inthe Dee Estuary.Large areas of the recently reclaimed flatterrain northeast of Backfill Queensferry and of the northeast coastal strip are occupied by estuarine alluvium. Backfill of quarriesand opencast coal sites often comprises the waste products of thequarrying Alluvial Fan [e.g. SJ 195 6791 and sandand gravel [e.g. SJ 1796811 extraction,and coal extraction [e.g. Thiscategory is morphological andthe sediments SJ 290 660, SJ 2686821 (as given for made evenwithin one deposit may be very variable. ground above). It may also include,however, Theyform where constricted streams and rivers household rubbish [e.g. SJ 18907246, SJ 264 660, flow into a less constrained area (e.g. the alluvial and SJ 286265001, andindustrial waste at floodplain of largea river) and thesediment approvedsites [e.g. SJ 1935 6928, SJ 2778 6600, carried by thestream is laiddown in a deposit and SJ 2155 62301. which increases areallydownstream. There may be apronounced grain-size decrease downstream Foundered Ground on the fan (e.g. gravelvarying downstream to fine sandand silt). . Some areas of founderedground are shown [e.g. SJ 209 604, SJ 2056 6010, SJ 2035 6054, Alluvial Terrace SJ 2066 6290, SJ 1890 6264, SJ 1900 6305 and SJ 1890 62501. These are sites wheredissolution These deposits areonly very localised and of theCarboniferous Limestone has induced small-scale. They usually comprisesimilar collapse founderingor of superficialthe material to otheralluvium and represent flooding overburden. They sometimes containlacustrine duringformerly higher levels of thestream or alluvium deposits (see below). river.

Landslip Lacustrine Alluvium Landslip affects bothbedrock and superficial These are small deposits generally, often occurring deposits. Some landslip is active [SJ 2065 6790, at the sites of temporary lakes whichexisted in SJ 2906781 or has recently been so [e.g. areas of sandand gravel during and immediately SJ 19787376, SJ 3128 65061. Most landslip afterthe Quaternary glaciation. An unusually recognised is probably of immediate post-glacial large area of this typeoccurs at [SJ 1785 75001. age and may not have been active for thousands Other areas are sometimes associated with of years. It must be stressed, however, that founderedground [e.g. SJ 2100 6044, SJ 2052 excavation of recorded landslips andparticularly 60 lo]. of thefronts of landslips is likely to reactivate them. Most landslipoccurs along steep-sided Head valleys, and is particularly common wherethe Head deposits are very variablein character and HalkynFormation or Coal Measures arethe represent downslope solifluction and redeposition bedrock. For example,there is extensive of glacial andother unconsolidated deposits, landslippingalong the valley of the Wepre Brook particularly during conditions of freeze and thaw. [SJ 278671 - 295 6811, some of which is still They are more extensive than shown on the map, active [e.g. SJ 290 6781, and along the valley of but veneers of head areoften less than 1 metre the Nant-y-Flint [SJ 194 750 - 223 7161. thick and on this criterion are not depicted. Head oftenaccumulates in the bottom of valleys as Alluvium areas of low relief. Alluvium(floodplain deposits) occurs along most of the more importantstreams and rivers. It Till (Boulder Clay) occupies considerabletracts of land along the Boulder clay is very widespread,particularly in courses of theAlyn and Dee rivers,and can be thecentre, east andnortheast of thearea. It is considered as activelyforming. It consists mainly extremelyvariable and was theproduct of direct of fine sands, silts and clays, with local gravels. deposition from melting glaciers. Clasts of 22 Deeside(North Wales) ThematicGeological Mapping varying size up to several metres are suspended in The boreholes are symbolisedaccording to a clay matrix. There is usually no orderor whetheror theynotprovide geotechnical beddingthough occasional beds of sand,gravel information.Although the geotechnical data may and silt may be intercalated. only be StandardPenetration Test data, a wide In thearea, there were two different sources of range of test dataand some interpretive boulder clay, with quite different suites of clasts, geotechnical reports are available (see Engineering clay matrices and grain-sizecharacteristics (see Geology) for some boreholes. Summary of Geology for further details). For most of the boreholes, information on the total thickness of the superficial deposits and the Sand and Gravel height of rockhead above Ordnance Datum (mean Thesedeposits are extensive along the Alyn and sea-level) is given. Rockhead is the base of the Wheeler rivers, north of Mold andimmediately weatheringprofile in bedrock. Where surface southwest of the Dee Estuary.They were level of the borehole was notrecorded, only the deposited by fluvio-glacial processes beneath and thickness of thesuperficial deposits is given. infront of the glacial ice-sheets. Theyare Where the boreholefailed to reachrockhead, the generally well- beddedand cross- bedded. The minimumthickness of superficialdeposits is coarser gravels often occur in lenses and channels. recorded,while rockhead is shown as being less Thedeposits oftenform moundy topography. In than (<), i.e. lower thanthe specified height between themounds, small depressions (kettle aboveOrdnance Datum. Thedensity of available holes) sometimesoccur in which silts, clays and boreholes is very patchy.Concentrations occur peat accumulatedswampyin andlacustrine along theroutes of road-schemes, most notably conditions (see Summary of Geology forfurther the A55, and at specific development sites. details). Rockheadcontours have been derived fromthe borehole datain areaswhere sufficientdata are Peat availableconstrainto them. additionIn to Some thinhill-peat occurs on the Clwydian Hills non-confidential boreholes, an even larger number in the southwest of the area, but it is too thin toL of confidential boreholes (mainlyrelating to be shown. Small peatdeposits occur in some British Coal opencastsite investigations) have kettle holes (see Sand and Gravel above). been used. The varyingheight of solid/drift boundaries (see ThematicElement, Map 2) also Thematic Element, Map 3 - Boreholes, Rockhead provideconstraint on thecalculation of rockhead and thickness of Superficial deposits contours. In areas free of superficial deposits, the topographiccontours are essentially rockhead Thismap shows thedistribution of sites of contours also, althoughextentthe of the non-confidential boreholes registered in the BGS weatheringprofile must also be takeninto 1:lO OOO/ 10 560 borehole system. Logs of these account. Rockheadcontours have only been boreholes are available for inspection at (or copies shown on the map for theseareas where they can be obtained from) the Aberystwyth Office of assist constrainingin theform of rockhead the BGS. contours underadjacent drift-covered areas. In In areaswhere the density of boreholes is great, areascovered by superficialdeposits, the some boreholes have been omitted.The criterion rockheadcontours depart increasingly fromthe for omission was that adjacent boreholes provided topographiccontours with increasing thickness of substantially the same information as those the deposits. Theform of rockheadcontours omitted. particularly indicates the form of buried channels related to the major river systems. Both the Alyn Shell andauger techniques were used for a large and Dee have deep,buried channel systems. The majority of the boreholes shown. These have a migrationandabandonment of channels is maximum depth of 30 Some boreholes, m. apparent along the Alyn River southeast of Mold. particularly for testingwatersupply, are considerablydeeper. A full list of the boreholes The River Dee has a buried U-shaped channel in is given inAppendix C, indicatingsurface level thenortheast of thearea, whose base reaches anddepth, detailed gridreference and other substantial depths (at least -54 m) below Ordnance information. Boreholes drilled as part of the Datum, suggesting it was probablyexcavated study are listed in Appendix F (see also Thematic duringthe Quaternary glaciation, when sea-level Element, Map 6). was much lower than at present. The channel was Deeside (North Wales) Thematic Geological Mapping 23

infilledinitially by glacialdeposits and latterly, has been worked and those where more than one withthe post-glacial rise in sea-leveldrowning seamhas been worked. Approximately 20 km2 of the valley northeastand east of Connah’s Quay, the area is knownto be undermined. No attempt estuarinealluvium accumulated. An asymmetric is made to indicatethe depths of workingssince partiallyburied channel extends from south to insufficientinformation is available. It is certain north,approximately between Mold andFlint. thatthe records of undergroundworkings are Glacial and glacially-related deposits largely infill incomplete.Thus, known mine-shafts, adits and most of the buried channels. coal waste tips are shown inareas without any mine plans. Thepossibility exists, therefore, of Thematic Element, Map 4 - Mining activities; shallow workings anywhere in the area where the Coal/Metalliferous coalmeasures arepresent and particularly so wherethe thicker seams (e.g. the Main and Thismap shows theareas mined for coal and Hollincoals) occur atoutcrop or shallow depth. metalliferousore, and aspects related tothat Thelikelihood of shallowworkings will decrease mining. A smallarea was mined for with increased superficial overburden. ‘cementstone’ (calcareous siltstone). The informationon coal mining is derived to alarge Many of themine-shafts and adits shown were extentfrom that of theBritish Coal database recorded during the field survey. Additional sites (OpencastExecutive, Coal Commission andother have been transferredfrom British Coal plans abandonedmine plans) and BGS archivaldata (whichindicate thevalidation of thedata). supplemented by recentthe survey. The Unrecordedshafts are likely to exist. A register informationon metalliferous mining is derived of all known shafts, totalling over 1000, with grid fromthe recent survey with supplementary BGS referencesand depth, are listed in Appendix D. archivalplans and maps. In the case of specific Thoseshafts which have been capped are siteinvestigations, the documents held by British differentiated onthe map. Capping does not Coal andat the Aberystwyth Office of the BGS implythat the shaft has beenfilled. Uncapped must be consulted. shafts may be wholly or partly filled. Backfilledopencast sites are shown, as areareas Coal Mining of madeground (waste tips) related to coal Coal has been mined in the area at least since the mining. No opencast sites areactive at present, Middle Ages and possibly earlier.Earliest butrecent opencasting at Ashfield House Farm workingswere likely to have been of coal at [SJ 313 6741was completedin 1987 and isnow outcrop,gradually developing intoshallow beingbackfilled and restored. British Coal have workings by aditsand bell pits. With theadvent applied for permission to develop an opencast site of greaterdemand for coal during the industrial at Pont Einion [SJ 260 6861 near Northop. revolution, deeper mining became prevalent. Itcannot be stressed too stronglythat shallow The map delimitsthe areas of underground workings,shafts and underground workings may workings for whichplans are available.Prior to exist in addition to those shown on the map, and 1872, there was no statutoryobligation to record thatthe limits of undergroundworkings are only plans of undergroundworkings. Theonly approximate.Unrecorded shafts, inparticular, informationrelating to very early mining derives area hazardand there have been anumber of fromsurface expressions (e.g. shafts,depressions, cases of such shafts collapsing in recent years, as waste tips)where recognisable. Even after 1872, for example in Flint [SJ 2424 72271 and Hawarden theplans lodged with the Mines Record Office [SJ 3167 66361. (copies of which are held by British Coal) were of Littleinformation exists as to themethods of veryvariable quality and accuracy. Few of the undergroundworking used specificat sites. plansrecord details of depth of workingsand However, it is known that two generalmethods many show little surface detail by which they can wereemployed. Theearliest technique of be positioned. On some plans, for example,it is large-scaleextraction was the‘pillar and stall’ clearthat the direction of north shown is method.This involved the selective extraction of inaccurate, to the extent in one instance of nearly coal, leaving up to 60% in position to support the 45’. Plottingsuch information is thereforeliable roof of the seam. Subsequentimprovements in to considerable error. techniqueincreased the efficiency of recovery. Theareas of undergroundworkings shown are Thuspanel working and longwall methods were differentiated into areas where only one coal seam used fromthe latter part of the19th Century 24 Deeside(North Wales) ThematicGeological Mapping

onwards(and probably applied in some cases to in Westphalian B is approximately 9 m. The seams already mined by pillar and stall). Many of original resources of the area were approximately the availablethe mineplans suggest longwall 300 milliontonnes (with approximately 200 extraction was used. Thisinvolved the complete milliontonnes in Westphalian Aand 100 million removal of coal from certain areas resulting in the tonnes in Westphalian B). Of this total, the extent controlled collapse of the unsupported seam roof, of recorded workings suggests that approximately On the map, no attempt is made to show areas of 15% of Westphalian Aresources and 30% of potentialsubsidence due to mining. This would Westphalian B resourceshave been substantially relateto the age and depth of workings,the extracted.The remaining ‘resources’ are not number of worked seams andthe thickness of necessarilyreadily available (e.g. due to superficial deposits. unrecordedworkings,substantialmine overburden,local thinning and washouts of coal Of the two mainmethods of mining,areas of seams), amenableor modernto extraction pillar andstall provide the greater potential methods,due mainly to theintense faulting and hazardto development. As alarge proportion of otherstructural complexities of thecoalfield. the seam was left as roof support,a borehole is Furthermore, no attemptcan be made to assess highlylikely to pass throughthe pillars (i.e. the thequality of individual seams. As coal seam ‘preservedseam) rather than adjacent voids. nomenclature varies across the area, a ‘correlation’ Furthermore, downward bowing of the seam roof of the local seam names withthe name usedby betweenpillars may suggestin aborehole that British Coal forthe whole of theNorth Wales only a thin seam is present, whereas voids close to Coalfields is given in Table 1. thepillars may still exist. Collapse of thepillars themselves can result in cavities, breccia pipes and voids inoverlying strata. In most parts of the Metalliferous Mining coalfieldany voids are now likely tobe filled Metalliferous mining was restricted to the west of with water. thearea and largely concentrated on the upper geological formations of Carboniferousthe Longwall extraction, used generally for the deeper LimestoneSummary(see of Geology - seams, typicallyresults in the collapse of the Mineralisation). The lead ore galena was the main unsupportedseam roof duringor soon after economic basis forthe industry with peaks in miningand further collapseis unlikely. Only the productionaround 1850 and 1895 (Smith, 1921). connecting ‘roads’ whichwerepermanently Silverextracted from the galena was avaluable supportedfor access arelikely to cause later by-product.Although mining on asmall scale subsidence problems and problems with voids. As persisted until the 1960’~~very little extraction has alarge majority of theseworkings on-shore are post-dated 1920.As little of thismining was related to minesabandoned by thelate 19th and recorded, no attempt is madeto show areas of early20th Centuries, little subsidence due to undergroundworking. Unlike coal mining, collapse is likely. Theconsiderable thickness of however,theareas of miningwere mostly superficialdeposits over much of thecoalfield restricted to narrow,relatively thin veins and also serves to mask and diffuse any collapse in the jointswhich tend to occurin conjugate sets. As underlyingCoal Measures. No deepmining has these veins can,in many instances, bewell takenplace recently. The only deep mine inthe defined by the linear chains of shafts and shallow area to continueproduction until the 1930’s was trial pits, displaying the veins themselves provides Bettisfieldcolliery (Bagillt) [SJ 215 7601 whose a good guideto the undermined areas. However, workingswere predominantly beneath the Dee in the case of thedeeper, usually more scattered estuary, thus posing no land subsidence problems. shafts, these were not necessarily sited directly on The most extensively worked seams are theMain the vein trends,and hence the positioning of the and Hollin coals (see Summary of Geology below). veins is subject to inaccuracy. A further problem Consideringthe area as awhole, approximately is that many of theveins departsignificantly 132 km2 is underlain by strata with coal seams of fromvertical, increasing the area of potential Westphalian A age,and 65 km2 by stratawith undermining. coal seams of Westphalian B age (andincluding The map shows selectedshafts only and the real the Main and Hollin coals; see Thematic Element, number of shafts(of very variable depths) runs Map 1 Summaryand of Geology).The intoseveral thousand. The archival field-slips cumulativeaverage thickness of all coal seams in andannotated photographs held byBGS must be Westphalian A is approximately 10 m whilethat consulted for the complete distribution.

Deeside (North Wales) Thematic Geological Mapping 29

Table 1. ‘Correlation’ of Coal Seam nomenclature for the northern ‘Flintshire Coalfield’ after British Coal

Local names Whole CoalfieldFlint, , Englefield andarea , Queensferry, , name Buckley name area and

Upper Stinking Upper Main Drowse11 Unnamed Massy, Small and Massy, Four Foot or Bind Powell Bind, Upper Two Yard, or King Bind or Powell Hollin Cannel, Upper Main, Bind, Bagillt Two Hollin or Two Yard. (Bottom leaf only, Yard or Yard Hollin Bench, Little or Cannel) Crank Little Crank, Little or Thin Quaker Brassey or Yard Black Bed Rough or Black Stone Main Bind Main Bind, Half Yard, Foul, Rough or Brick Main Five Yard or Three Yard Main Lower Bench Three Yard or Brassy Lower Bench, Little, Two Foot, Finger or Half Yard Crown Double, Upper Double or Double Roll Diamond, Five Foot, Two Foot, Four Foot or Jubilee Upper Red Durbog or Lower Double King Lower Red Yard, One Yard or Two Foot Cannel, Red, Two Foot or Three Foot Stone Double, Cannel or Four Foot Wall and Bench, Stone, Wood Pit, Mount Pleasant, Yard, New, Five Foot or Four Foot Nine Foot Rider Unnamed Nine Foot Rider or Wall Nine Foot Hard Five Quarter, Three Yard, Main, Nine Foot, Dirty or Upper Four Foot New Three Yard, Two Yard, Thicker Six Foot Nant Brassy, Best, Hard, Dirty, Double, Nant, Upper Four Foot, Upper Middle or Five Foot Latchcroft, Four Foot, Dirty or Yard Ruabon Yard Soft Five Quarter or Four Foot Yard, Arley, or Cannel Premier Four Foot, Bottom or New Premier, Lower Four Foot, Lower Five Foot, Five Quarters, Latchcroft, Four Foot, Wall and Bench or King Llwyneinisn Half Yard Queen, Yard or Small Half Yard or Queen Chwarelau Little or Lower Yard Little Deeside (North Wales) Thematic Geological Mapping 29

Furthermore,the extensive shallow-level removal Anattempt was made during thefield survey to of oresduring the past would necessitate that categorise shaftsinthe northern half of the future mining would haveto exploit resources at miningdistrict into three types, reflectingtheir some depth and this would pose problems of mine hazard potential: drainage (see Drainage Tunnels below). 1. Capped shafts (though not necessarily filled) 2. Uncappedshafts (though not necessarily open Cementstone at surface) and deep pits This was extracted from a number of adits in one 3. Probable trial pits and shallow shafts. small areanear Holywell [SJ 193 7541. Theadits These were coded by colour on the air photos and are confined to the Halkyn Formation. field slips, butonly those in categories 1and 2 were transferredtheto 1: 10 OOO/ 10 560 Drainage Tunnels ‘geological standards’ andare thusselectively As metalliferousmining reached deeper levels, representedhere. Figures 5a and 5b reproduce drainage became theprincipal limiting factor of theoriginal categorisation forthe main area of development of the mines. Consequentlylengthy mining on Halkyn Mountain where the number of drainagetunnels were constructed,connecting shaftsandtrials is at its greatest. The several of the more important mines. Of these, categorisation of types 2 and 3 was highly the two maintunnel schemes werethe Halkyn or subjective. Some deepshafts which areopen at Deep Level Tunneland the Milwr Sea Level the surface are readily assigned, but the majority Tunnel. Gradients of approximatelyin1 1000 are closed, at least atsurface (due to collapse), carriedwater northwards. The has though they may be open at depth. Therefore the provided water for industrial use recently, and the assignment was mainly influenced by the volume tunnel is maintainedwith access using the of spoil material surrounding the shaft site. These winding gear at‘Hendre Mine’ [SJ 2015 67771. areas of spoil form ring-like ramparts around the Other drainage tunnels, including branches on the shafts,which are themselves usually preserved as main tunnels, are also shown. depressions. The larger the volume of spoil relative to thediameter of theshaft-site, the Thematic Element, Map 5 Resources (Bedrock) greater is the likelihood of it having been a deep - except Coal/Metalliferous shaft, rather than an ephemeral trial pit. Only the - more extensiveareas of madeground are shown Thismap shows thedistribution of areas within on the map. However, the close spacing of the which bedrock resources, apartfrom coal and shafts results in many areas, along veins, in chains metalliferous deposits, are or have been extracted of mounds of made ground (see Thematic and wherepotential may exist forfurther Element, Map 2 and rear cover photograph 1). exploitation. It has beencompiled from the 1: 10 000 and 1: 10 560 geological maps.Where Figure 6 is a detailedmap of thedistribution of applicable,the resource areas are shown as being shaftsin the Loggerheads Country Park, and the limited by superficialdeposits more than 10 m Cefn Mawr and Coed Pwll-y-blawd Site of thicksince it is consideredthat most bedrock Special Scientific Interest. resources areunlikely to be exploitedbeneath an It is increasingly common practice to attempt land overburdenwhich exceeds that thickness. It must restorationin areas of previous lead mining by be emphasizedthat this 10 mlimit is only bulldozing flat the made ground. Consequentlyin approximate as there are many parts of the study some areas, the number and density of shafts will areain whichthere is insufficient borehole remain unknown. informationorfield evidence to permitthe drawing of anaccurate 10 m isopachyte of Ores areprincipally restricted to veins, joints, superficial deposits. pipes and some bedding planes (see Summary of Geology - Mineralisation).Theyoccur as Activequarries and pits andthe larger disused discontinuousdeposits whose distributionand quarriesand pits are shown; sites of completely concentration are unpredictable. As modern backfilledquarries and pits (where known) are large-scale base metal extraction tends to rely on also shown since these could represent 9 possible prospects of predictable,albeit often relatively hazard for developers. Eachquarry pit,or low, concentrations,the ore deposits inthe area whether active or disused, is annotated to indicate would seem not to be a viable prospect under the type of resourcewhich was obtained from it; present or foreseeable economic conditions. the same annotation is given with each heading in 30 Deeside(North Wales) Thematic GeologicalMapping thisdescription. A few of the disusedquarries Llanarmon. andpits lieoutside indicated resource areas. TheLeete Limestone, which separates the These either liewithin resource areas which are Loggerheads and LlanarmonLimestones in the too small to show on the map or were for clay, a vertical succession, comprisesinterbedded resource which is not shown in detail on the map porcellanous andfine-grained limestones of (see under Clay). moderate purityand lithologies similar to the LlanarmonLimestone. It has beenworked on a Limestone (L) small scale in the past. TheCarboniferous Limestone has broad a The Foe1 Formation, the thin basal division of the north-southoutcrop covering some 39 sq km in CarboniferousLimestone, is largely composed of thewestern part of thestudy area, extending dark impure limestone and has not been included from Holywell inthe north, through Halkyn on the resource map. Mountain, and Loggerheads to Big Covert [SJ 200 6001 in the south. Most of this outcrop is Limestone is withoutdoubt thesingle most freefrom thick superficial deposits. Onprevious importantresource within the study area. It is geological maps the limestone has been shown as present in enormous quantity; the total amount of one unit; inthe recent survey six divisions theoreticallyworkable limestone, taking Ordnance (formations)have been recognised within the Datum as a base level and an average surface level limestone andtheir areas of outcropare now of theterrain as +250 m OD, is approximately known in detail. The sequence of formations and 2.75 x 10" tonnes. Obviously onlya fraction of their thickness variation is given in the Geological this amount is likely to be worked, at least in the Sequence anda detailed description of therock foreseeable future,and many factorseffectively types in eachformation inthe Summary of reducetheamount of the resource actually Geology. Physical properties of the limestones available. These include geological factors such as and estimates of theirpurity, derived from the presence of shale and sandstoneunits in the Harrison and others (1983) and related to the new upperpart of thesequence and past mining for stratigraphy,are given inTable 3. Thehigh metalliferous deposits, areas sterilised by housing, purity reef limestonesmentioned in that report andenvironmental factors such as theeffect on (p. 75) as occurringbetween and Mold topographypresencethe and of SSSI's. are not present within the study area. Nevertheless, less than 1% of the total volume has so far beenextracted and one of the most The limestones sf the Cefn Mawr Limestone and importantresults of thisstudy is thatthe new Minera Formation have been grouped together on detailed geological maps will enable thefuture theresource mapsince they have similar exploitation of the resource to be carried out more characteristics. significantThe difference effectively now that the areal extent and thickness between theformations is thattheMinera of thevarious limestone types is more closely Formation,which is presentonly from defined.Deepening of some of thequarries can Moel-y-Crio southwards,includes interbedded be considered,rather than further lateral quartzitic sandstones which are not present in the expansion,particularly ifthe drainage of the CefnMawr Limestone. The limestones of the northern part of the outcrop via the Milwr tunnel CefnMawr Limestone areinterbedded with is maintained. mudstones, withtheproportion of mudstone increasingtowards the top of theformation. The The Loggerheadsand Llanarmon limestones are Minera Formation has been worked in the past for formations of predictableand constant nature; limestone, sandstoneand silica sand; the Cefn they are of high purity and good aggregate quality Mawr Limestone is worked in all theactive and can generally be expected to be of sufficient quarries (see Table 2 below) within the study area. strengthand durability to be used as a roadstone (base andsub-base) and concreteaggregate TheLoggerheads Limestone, in. contrast to the (Harrisonand others, 1983). TheCefn Mawr Cefn Mawr, is of very high purity and has a very Limestone and MineraFormation contain low mudstonecontent. On the resource map it is limestones of similaraggregate quality but they grouped with the Llanarmon Limestone which has also contain a highproportion of mudstone/shale similarcharacteristics. It is worked in the waste; however, the association of limestoneand northernfive of activethe quarries. The shale is particularly useful for cement production. LlanarmonLimestone is not at present worked in TheMinera Formation, however, has the thestudy area; it is quarriedfurther south,near additional problem that sandstone bodies within it Deeside (North Wales) Thematic Geological Mapping 3 I

Table 2 Active limestone quarries at the time of survey detractfrom its value as aprimary resource for the cementindustry. The Leete Limestone and Foe1 Formation are more variable in character and QuarryOperatornameFormation Grid their resource potential is therefore less Referenceworked predictable and harder to generalise; however, the combinedthickness of these twoformations Pant-y-pwll-dwr North West SJ 190 720 CefnMawr, Loggerheads representsonly a small proportion of the limestone sequence as a whole. Pant Wimpy plc SJ 199 702 CefnMawr, Loggerheads Sandstone (S and Sf) Hendm Alfred SJ 193 681 CefnMawr, McAlpine Loggerheads Two types of sandstone are shownon the map. Quarries Ltd These have been denoted as quartzitica) Trim Rock Tiicon Ltd SJ 191 660 CefnMawr, sandstone (S) and b) feldspathic sandstone (Sf). Loggerheads Cefn Mawr Castle SJ 200 634 CefnMawr, Thequartzitic sandstones aretheKinnerton Cement Ltd Loggerheads Sandstone Formation(described separately under Aberduna Pioneer SJ 204 618 CefnMawr Moulding Sand) and sandstone beds withinthe Aggregates (UK) Ltd HalkynandMinera formations. Theyare sandstones with a very high quartz (silica) content Burley Hill Welsh SJ 203 600 CefnMawr (partly on study Aggregates anda low content of feldspar. In the lower part area) Ltd of thestratigraphical sequence these sandstones containanappreciable proportion of calcium carbonate either as included fossil (shell) debris or as intergranularan cement. Normally the quartzitic sandstones arehard, but locally and unpredictablythe more carbonate-rich types may weather to a disaggregated andvery pure silica sand. Thefeldspathic sandstones include the Gwespyr Sandstone at the top of the Halkyn Formation and all the sandstones within the Coal Measures. They containhighera content of feldsparthan the quartzitic types and may also have an appreciable .content of oxides. Ingeneral they are softer than the quartzitic sandstones and are more liable to weather along bedding planes orother planes of weakness in the rock. Both types of sandstone have been widely exploited in the past, mainly in small quarries, for building and walling stone. None is now used for that purpose. Some of thesofter sandstones withinthe Buckley Formation have been used in conjunctionwith the fireclays (see under Clay). Theaggregate quality of thesandstones is not known in detail though their mineral composition andweathering characteristics suggest thatthe feldspathicsandstones are likely to be of poor to moderatequality while thequartzitic sandstones may locally beof good quality.However, there areanumber of factorswhich militate against theirexploitation for this purpose. Firstly, most of the sandstone beds, particulariy within the Coal Measures, arerelatively thin and often change rapidly in thickness, and thus are not amenable to large-scale quarryingoperations; secondly, the Table 3 ' Sun~naryof mechanical and chemical property data from limestones. (Adapted from Harrison and others, 1983)

Purity Mechanicalproperties

Purity Insoluble Flakiness AIV residue Index I7tI Cef n hqawr Dark argillaceous Generally limestonewith shales 1.2 31.9 27 51 20 - 24 123 - 25 5.0 9.1 lowpurity - - -

Loggerheads Massive pale grey Very high limestone purity 0.2 - 1.5 14 - 31 20 - 25 10.2 - 11.8

I I I I I Leete Dark grey fine-grained Medium limestone and massive purity No dataavailable pale grey limestone \

Llanarmori Massivepale grey Veryhigh limestone purity 24 - 35 I 21 - 25 I 25 '1 8.6 - 10.7 Oel - 3a6 I Deeside (North Wales) Thematic Geological Mapping 33 weatheringcharacteristics of the sandstones are lies in twoeastward-dipping fault-bounded veryvariable and unpredictable, especially the north-southstrips from Lane Endto the Etna quartzitic type where a hard sandstone can change Brickworks [SJ 2866521 andfrom Hawkesbury laterally to adisaggregated sand within a few [SJ 279 6451 to the Castle Brickworks [SJ 277 6611. metres; thirdly,they are closely adjacentto very Inthe eastern stripthe workings are limited by largeresources of limestone of consistent and faulting, while inthe western strip the worked proven aggregate quality. clays dip underincreasingan thickness of sandstoneoverburden andthus become less The disaggregatedquartzitic sandstones (silica economical to work. Additionally,the siting of sand) have, inthe past, been worked south many of thebrickworks on the eastern parts of [SJ 2096051 of Moel Findeg.There are probably the outcrops has resulted in partial sterilization of appreciable resources of this material, butthe the resource. apparentlycompletely unpredictable nature of its occurrence makes it impossible to comment on its There are three other areas in which the Buckley potential. canIt only be assessed locally by Formation is present (see Thematic Element, Map detailed investigation on a site-specific basis. 1 - Bedrock Geology). Inthe first of these, between Tirlasgoch and WaredWood, there is Moulding Sand (MS) some evidence, along theAlltami Brook, thatthe lower, workable, part of the formation is present. Mouldingsand is obtainedfrom the Triassic However, most of thearea is coveredin thick Kinnerton Sandstone Formation Kinnertonat superficialdeposits (see map). The other two Bank Quarry [SJ 330 6041 owned by areas are between andGwysaney Hall Thos Dodd & Son Ltd.Atthis locality the [SJ 2286651 and along themargin of the Dee sandstonehas weathered to a disaggregated soft Estuary at Bagillt. Both areas are largely covered sandwhich is easily won. It has alarge areal with thick superficial deposits and have not been extentin the eastern part of thestudy area (see included a resource. ThematicElement, Map 1 - Bedrock Geology), as butonly around Kinnerton is it covered by less Thinner fireclaysoccur at various levels - than 10 m of superficial deposits. Since the throughoutthe Coal Measures and theHalkyn decline inthe steelindustry, particularly at Formation. These, togetherwithother soft Shotton, the demand for moulding sand has fallen mudstones, have been dugfor brickmakingand considerably and mostof the output is now used otherproducts in various locations, for example for general purposes. Ruby Brickpits [SJ 206 6781 inthe Halkyn Formation and the Standard Brickpits [SJ 290 6501 Clay (a inthe Coal Measures. Theyare not now utilised andsince such clays andmudstones occur so The most importantclay resources are those commonly withinthe Coal Measures andHalkyn withinthe Buckley Formation, but clay been has Formation it is notfeasible to categorizethem as worked at variouslocations at other horizons a resource on the map. withinthe Coal Measures andinthe Halkyn Formation.Additionally there have been very Many of the old clay pits have been or are being small local workingsin Till (Boulder Clay). Only used as disposal sites forindustrial or household the Buckley Formation clays areindicated as a waste (see ThematicElement, Map7 - resourceon the map. The only working pit is in Hydrogeology and Water Supply). the Buckley Formation, at LaneEnd, Buckley [SJ 288 6391 operated by Butterley Brick Ltd. Chert (Ch) The main productsfrom the Buckley Formation Thethickest development of chert is atthe base have been firebricks,acid-resistant bricks and of theHalkyn Formation, particularly along the housebricks. easternside of. HalkynMountain (up to150 m The Buckley Formation has an estimated thick). Thinner beds arepresent at similara maximum thickness of 250 m but only the lowest horizon towards thesouthern part of thestudy beds havebeen exploited. In generalterms these areaaround Moel Findeg. On HalkynMountain comprise about 15 m of fireclay overlain by 15 m the purest chert is found in the middle part ofIts of sandstone (GSGB 1920b, pp. 167-82); at some development. The deposits have been worked in pits the lower part of the sandstone, which is the the past for silica for glass making and silica most siliceous and least feldspathic part, has been bricks,moreandrecently for aggregate. utilised as well as thefireclay. The worked area Although not utilised at presentwithin the study 34 Deeside(North Wales) Thematic GeologicalMapping

area, it should be emphasized that chert is a very parameters of thedeposits over the whole of the pure form of silica and that workable deposits are contractarea are those used by the IMAU.Thus comparatively rare nationally. adeposit stated to be 'potentially workable' must satisfy the following criteria: Clay and Sand in pipes (CS) 1- Thedeposit should average at least 1metre in These deposits are found in large solution hollows thickness. and steep-sidedpipes thein Carboniferous 2. Theratio of overburdento sand and gravel limestones. Theycomprise soft clays andsands, should be no more than 3:l. probably of Tertiary age, and have been worked 3. Theproportion of fines(particles passing an in the pastthe in for pipe-clay and porcelain 0.625mm BS sieve)should not exceed 40 per manufacturenear Rhes-y-Cae [SJ 190 7101, cent. Colomendy [SJ 203 6201 andelsewhere (Maw, 4. The depositshould lie within 25 m of the 1867; Strahan, 1890;Walsh and Brown, 1971). surf ace. The deposits are too small in area to show on the Forparticle size analyses agrain size definition ThematicElement Map and are unlikely tobe of based onthe geometric scale 1/16 mm, 1/4 mm, economic value in the future. 1mm, 4 mm, 16 mm, and 64 mm has been adopted.The boundaries between fines (that is Calcspar (Ca) the clay and silt fractions) and sand, and between Calcspar (crystallinecalcium carbonate) occurs in sand and gravel are placed at 1/16 mm and 4 mm varying quantity along mostof the mineralized respectively.The area previously assessed by the veins withinthe Carboniferous limestones. It has IMAU (Sheets SJ 16 and 26) has been resurveyed, been workeduntil recently along a N-S vein and consequentlythe boundaries of the sandand [SJ 186 676 - 1876621 south of Hendre. graveldeposits on thepublished map (Ball and Although it is a common mineral it rarely occurs Adlam, 1982) have beenamended. Additionally in sufficient quantity to be worthwhile exploiting. theareas indicated on that map as being "potentially workable" beneath superficial deposits Thematic Element, Map 6 - Resources - Sand have also beenamended inthe light of evidence and Gravel fromrecent boreholes. No additionalparticle size analyses of depositswithin this area have been Thismap shows theknown distribution of sand carried out and the grading diagrams on that part andgravel within metre1 of thesurface. of theThematic Map are taken from the IMAU Deposits less than1 metre in thickness have been Report. A number of shallow boreholes were put omitted.Thedeposits are almost entirely down on sheets SJ 17 NE, 17 SE, 27 NW, 27 SW, classified as Glacial Sand andGravel on the and 27 SE part of thepresent contract. The ThematicElement, Map2 - Superficial as logsof these boreholes and the results of particle (Unconsolidated) deposits; one small area size analyses of the sand and gravel deposits [SJ 239 7 181 of Alluvial (River) Terrace south of provedinthem are detailedinAppendix F; Flint is also included.Areas of potentially gradingdiagrams derived from these results are workable sand and gravel (see below) beneath shown on the Thematic Map. overburdenare also shown withthe thickness of the deposits as proved in selected boreholes. Sites The main potentialresource outside the area of active and former workings for sand and gravel alreadycovered by theIMAU Report lies along are shown; gradingdiagrams are given for the slopes abovethe Dee Estuarybetween deposits proved both in shallow boreholes sunk as Greenfield and the Lead Brook [SJ 259 7031. The part of the present contract (see Appendix F) and deposits arepatchy and some areas,notably at in those putdown earlier by theIndustrial Greenfield, Bagillt and thesouthwesternin Minerals Assessment Unit(IMAU) of BGS. At outskirts of Flint, have been obscured by urban present there are two active pits within the study development. A second resource area lies between area, at [SJ 2166701 operated by Hawarden and Warren Mountain [SJ 320 6301; the Welsh Aggregates LtdandStar at Crossing thickestdeposits are around Hawarden but these . [SJ 175 6801 operated by Tilcon Ltd. are now largely builtover. The limited number of boreholes inboth areas precludes a detailed Thearea covered by sheets 16 SJ 26 has SJ and estimate of the value orquantity of thepotential previously been assessed by theIMAU, and the resource. results published (Ball andAdlam, 1982). For consistency, thecriteria used to describe the A number of factors affect the ease of working of Deeside (North Wales) Thematic Geological Mapping 35 thesand and gravel deposits; these includetheir been subdivided by both waste type and period of topographic formand the degree of lateral tipping as both of these affect the quality of the variationwithin them. In some areas, as around leachateproduced. They represent potential risks Padeswood [SJ 275 6201, the deposits havea to groundwater quality. markedmoundy topography with anumber of Theaverage annual precipitation for thestudy enclosed hollows (kettle holes) which may be area varies from 700 mm inthe Dee Valley to filledwith peat and/or clay to aconsiderable over 900 mm aroundHalkyn and . depth.One such hollow [SJ 237 7 101 north of Annual evapotranspiration is about 450 mm. was proved to a depth of17.4 m. Thevariable thickness of thesand and gravel in Within thearea there are severalgroundwater suchmoundy areas, togetherwith the infilled abstractions for bothpublic andindustrial hollows, renderssuch deposits more difficultto purposes, although most of thewater used comes work on a large scale than flat-topped spreads of from surface and groundwater sources outside the sand andgravel as at Rhosesmor. All the sand area. and gravel deposits show rapid lateral changes of lithology. Inparticular the coarser gravels are Silurian oftenconfined toirregular channels within a The induratedThe mudstones subordinateand deposit of generally finer grade.The proportions sandstones of theElwy Groupare relatively of thevarious types of clast withinthe gravels impermeable. However, small domesticsupplies also vary considerably.In the south-western part of soft water are locally obtained from springs. of the study area, between Cilcain and Llanferres, themain clasts aresiltstones and feldspathic sandstones, whereas inthe remainder of thearea Carboniferous limestone, quartziteand igneous rocks are The CarboniferousLimestone is the second most predominant. important aquifer in the district in terms of water usage. However, drillingfor water is highly Approximately 43 sq km of thestudy area has speculative as the limestones have minimal sand and gravel either at the surface or concealed primary porosities and permeabilities,and beneathoverburden. Extrapolation fromthe groundwater movement is restricted to fissures results obtained by Ball and Adlam (1982) for the enlarged by solution. Fewboreholes have been Mold area,with additional information obtained drilledin the area althoughthe fissures are during the present study, indicates a total volume as, commonly fault-controlled,theyneitherare of deposit of between 3 x lo9 and 4 x 109m3 regularlyspaced nor extensively interconnected; (approximately 7.5 x lo8 million tonnes). Of this failure to intersect a fissure generally results in a at least 10% has already been sterilized by the dry hole. Althoughfissures are relatively sparse, urbanareas of Mold, Bagillt, Flint,Greenfield wherethey do occur they tend to be large and, andHawarden. The areas of greatest potential therefore,groundwater movement can be rapid. resource liealong and adjacent to the valleys of Flows fromfissure systems issue from alimited theAlyn and Wheeler rivers,and between Mold number of springs whose flowrates vary and Flint. considerablywith time, and can decrease by an order of magnitude indry weather.Tunnels Thematic Element, Map 7 Hydrogeology and - through the limestone, associated with old mineral Water Supply workings inthe lead andzinc veins, intersectthe The map indicatesoutcropsthe of the fissure systems and have had asignificant effect CartboniferousLimestone, the sandstones within onthe hydrogeology of thearea. Two of these, the Namurian and Westphalian and the Kinnerton the Milwr Sea Level Tunnel and the Halkyn Deep Sandstone Formation. The superficialdeposits Level Tunnel,are now used for watersupply. have been omitted from this map for clarity; they Where the limestone outcrop is free of superficial are shown on Thematic Element, Map 2. It shows deposits,recharge is effectiveequal to the locations of thesprings, wells and boreholes precipitation. that are licensed to abstract groundwater, and the Under low-flow conditions,water from the positions of the main tunnels.Groundwater level limestones is generally hard, but of good quality; contours are indicated in the Kinnerton Sandstone. theconcentration of metal ions may be high. Inaddition the positions of past andpresent However, after heavy rain,supplies from both landfill waste disposal sitesand storage lagoons, boreholes andsprings may become turbidand fornon-inert wastes, aremarked. These have 36 Deeside (North Wales) ThematicGeological Mapping pollutedwith high concentrations of suspended development of fissuresbut boreholes are rarely solids, organic matter, bacteria and nitrates. failures. Water inthe fissures is supplied by inflowfrom pores in the matrix of the rock. Water fromthe Namurian strata is used from Over 50 l/s have been obtained from the 760 mm springswhich occur atthe junctions of the diameterboreholes at Shotton [SJ 3380 7110 and jointed sandstones with underlying less permeable SJ 3 197 7256), butyields of30 l/s are more mudstones.Boreholes that fail intersectto common. Apartfrom a few verysmall areas in water-bearingjoints and fissures are generally the south , where the aquifer is recharged by the dry,and only one low-yielding borehole is Brad Brook, theentire sandstone outcrop is recordedfrom the area. However, tunnels and overlain by boulderclay or estuarine alluvium. aditsassociated with old lead and zinc workings Consequentlythe northern part of theaquifer, have been used for water supply. The water is of where abstractions occur, is being recharged from good quality,but hard. Iron may be a problem, areas further to the east. and other metals are present where the water has been in contact with mineral workings. Thequality of water is good, but hard; bicarbonateconcentrations in excess of 360 mg/l Themudstones and well-cemented sandstones of havebeen recorded. Chloride concentrations are the Westphalian have low primarypermeabilities. generally less than 100 mg/l,but higher values However, water occurs in the sandstones to depths of fewa hundred metreswithin joints and occur locally. fractures caused by miningsubsidence. The Superficial deposits yields of boreholesdepend on thenumber of jointsintersected but 5 l/s(litres per second) is Most of thedistrict is overlain by superficial notuncommon and a 123 mdeep, 200 mm deposits.These vary from impermeable boulder diameter borehole at Mold [SJ 2418 63483 yielded clay, estuarine alluvium and lacustrine deposits to 16.1 l/s frombeneath 13.4 m of superficial permeablefluvial and glacial sands and gravels. deposits.Despite the factthat disused colliery Theyoften exceed 20 metresin thickness (see workingscontain considerable storage, yields are Summary of Geology)and may exceed 90 metres rarely sustained in the long-term. This is because locally. Yields of about 12 l/s have been obtained recharge is limited by theseparation of the from a 4.1 m thick gravel horizon at the base of a aquiferinto isolated fault-blocks and by an 9.3 m deep borehole at Hendre [SJ 1828 67661 and extensivecover of low permeabilitydrift of froman 8 mthick sand and gravel deposit in a considerablethickness. Springs occur where the 55 m borehole atSandicroft [SJ 3377 67421. more permeablehorizons crop out. Locally, However,elsewhere recorded yields are generally beneathdrift, overflowing conditions exist. The about 5 l/s. Sand and gravel overlying an aquifer quality of thewater is variable,but usually is an importantfactor allowing recharge, both non-potable.Total dissolved solids are in the directlyand also indirectly,where there is range 500-2000 mg/l (milligrammes per litre) and hydrauliccontinuity between the aquifer and a ironconcentrations are often high. Thewater river. tendsto be polluted by coal-miningactivities. A Thequality of waterfrom these deposits is borehole, 76 deep,m Ferryat Bank Farm variable.Unpolluted sources willbe chemically [SJ 3280 68701, which had a yield of 4.4 l/s when similar to, butharder than, any surface water initially completed, is used for spray irrigation. withwhich they are in continuity. However, the water is susceptible to contaminationfrom Kinnerton Sandstone Formation agriculture,waste disposal sites, septic tanks and TheKinnerton SandstoneFormation is themajor leakysewers, except where the permeable glacial aquiferin the district despite its small outcrop depositsare protected by overlying till. Nearthe area.Theporosity of theweakly-cemented coast, the water is liable to saline intrusion. sandstonesranges from 20%to 30%. Intrinsic permeabilities vary but even the higher values are significantly less than the hydraulic conductivities encounteredin the field. This is because water movement is controlled by fissures which provide nearly all the permeability and are encountered to depths of at least 100 metres.Transmissivities andyields vary considerably depending on the Deeside (North Wales) Thematic Geological Mapping 37

ENGINEERING GEOLOGY of low quality(often by drillers only, or worse), poorly located boreholes, and no interpretation The Geotechnical Database (Category Four). Classification of the geological formationsinto Of the 68 reports,15 fell in CategoryOne (the groupings with similar engineering properties was best), 24 in Category Two, 25 in CategoryThree carried out using geotechnical data extracted from and 4 inCategory Four. Alimited comparison site-investigation reports on sites within the study was made of data from the different categories of area. As much of thearea is rural,coverage of report.One particular deposit (Till) was selected these reports is restricted. In general, thereports anda simple statistical analysis of some of the are of two types in terms of their areal coverage; geotechnical data carried out for selected Category firstly, they relate to development and other sites One test samples alone (322 samples), and for all inand around current urban areas (for example, test samples (1645 samples). Thegeotechnical Mold, Connah's Quay,Flint, Bagillt and classification test parameters chosen were moisture Holywell); and secondly,they relate roadto content, liquid limit, plastic limit, plasticity index, developments (particularly the A55, but including bulk density, clay, silt,sand and gravelcontents, the A550/491 from to Ewloeand and the N value (the number of blows) from the bypasses to Mold ).and The S.P.T. addition,In data from consolidation, distribution of boreholes for whichgeotechnical strength,compaction and chemical tests were data are available is shown on Thematic Element, compared visually. The comparison of the Map 3. Thisinformation is supplemented by summary is shown in Tables 21 and 22. limited information from publications. The analysis carriedout measured whether the The geotechnical information used here to classify two sets of data differ significantly, in statistical geological formationsin engineering terms is not terms, for each parameter. For all parameters, the necessarily representativeor comprehensive. For two sets of datawere identical within 90% some formations(for example, the mudstones of confidencelimits (two- tailed Z- test). Visual theElwy Group) no geotechnical dataare inspection of consolidation,compaction and available. Forothers (for example, the Kinnerton chemical test data showed theresults from the Sandstone Formation)data are limited to those two sets of test samples werevery similar. Only from ahandful of boreholes. For most of the inthe case of results fromthe quick undrained formations, geo technicalinformation is only triaxial test was there any divergence. The reason available for part of theiroutcrop. Consequently, for this is not known but it may be related to the summary values of geotechnicalparameters given way resultsare quoted inthe reports. Sometimes for the various formations should be considered as only undrainedshear strength is quoted. In this ageneral guide only and should not be used in case the undrained angle of friction is assumed to detailed foundation design calculations. be zero andthe undrained cohesion equals the Geotechnicaltest data were obtained for 4273 undrainedshear strength. In other reports, both individual samples (a singleStandard Penetration undrained cohesion and angle of frictionare Test [S.P.T] counting as onesample) and these given. Consequently, cohesion will beless than datawere contained in 68 individualreports. theshear strength. Other factors, such as the Whilst this geotechnical data set may be relatively sampling method used, may have contributed to small comparedwith some other areas of similar thedisparity but analysis of this is beyond the size, considerable time was required to extract and scope of this report. analyse thedata. To determine whether it was Fromthis limited statistical analysis it may be necessary to extract all geotechnical data to concludedthat for Till, at least, there is no understandpropertiesthe of formation, a significant difference in the summary geotechnical site-investigationreports were divided intofour values obtained from a small (20%) sub-set of the groups based on theextent of thefactual test samples comparedwith the complete set. informationaccompanyingand interpretive Thisimplies that considerable time can be saved reports.Subjective assessment of the quality of in handlingand analysis of thegeotechnical data data was also attempted.The nature of reports by careful selection of limited "good quality" data a ranged from those containing wealth of only. However, further work is required to geotechnicaldata, apparently of good quality, confirm that this conclusion applies generally. withdetailed engineering geological logs and accompanying interpretive reports (Category One), Results of thefollowing geotechnical tests and to those thatcontained no geotechnical data, logs measurements(laboratory andin-situ) were 38 Deeside(North Wales) Thematic GeologicalMapping abstracted from all categories of site investigation programme. report and entered into the database. Itshould also be notedthat no account is taken 1. Standard Penetration Test (S.P.T.) here of problemsrelating to past mining. These 2. Rock Quality Designation (R.Q.D.) aredescribed in the section relating to Thematic 3. Moisturecontent Element,Map 4 - Miningactivities; 4. Liquid limit Coal/Metalliferous.The suitability of anysite 5. Plastic limit will be dependent,therefore, not only on the 6. Bulk density engineeringcharacteristics of thenear-surface 7. Drydensity deposits but also on the likely effect that mining 8. Triaxial (drained and undrained) may have (in terms of collapse, old shaft location 9. Consolidation etc.) upon the integrity of the proposed structure. 10.Permeability 11.Particle size analysis (P.S.A.) Engineering Classification of the Rocks and Soils 12.Compaction 13.California bearing ratio (C.B.R.) The division of the rocks and soils of the Deeside areaintogroupings of materials of like 14.pH engineeringproperties is based,in part, on the 15.Sulphate content 16.Specific gravity engineeringproperties themselves, as determined inthe various tests, and partly on geological For most samples, onlya few of these tests had grounds. Forexample, whilst onthe basisof been carriedout, and rarely was a full range of theirengineering properties there is little reason test resultsavailable forparticular a to differentiate estuarine alluvial sands from sands lithologicallgeotechnical unit within one borehole. of otherforms of alluvium,they can be clearly Descriptions of the tests are provided in Appendix separated geologically (see ThematicElement, B. Map 2). Hence,they have been classified separately for engineering geological purposes. Theclassification of rock (bedrock)and soils (superficial deposits) in terms of their engineering In engineeringterms, the rocks and soils of the characteristics was aided by analysis of results area can be divided into eight broad groupings: from the more commonly performed tests: 1. Rock 1. Standard Penetration Test (S.P.T.) 2. Fill, made ground 2. Moisturecontent 3. Peat 3. Liquidlimit 4. Normally consolidated cohesive soils 4. Plastic limit 5. Loose non-cohesive soils 5. Bulk density 6. Heterogeneous soils (cohesive/non-cohesive soil 6. Undrainedtriaxial mixes in varying proportions) 7. Consolidation 7. Overconsolidated cohesive soils 8. Particle size analysis 8. Dense non-cohesive soils Results of this analysis (tables 4-22) give Ingeneral, group 1 materialsareshown on summary values of the geotechnical properties for ThematicElement, Map 1 - Bedrock Geology, the different soil units(superficial deposits). andgroups 2-8 on theThematic Element, Map 2 Insufficientdata are available to producea - Superficial(Unconsolidated) deposits. It should summarytable of geotechnicalproperties of rock be noted,however, that the simple division of units (bedrockformations) other than the rock and soils is complicated by gradation across mudstones of the Buckley Formation, the theweathering profile of bedrock.Geotechnical Productive Coal Measures and Halkynthe dataforweathered deposits arenot usually Formation (Tables 4- 10). available,except for the Buckley Formation, the Productive Coal Measures andHalkynthe Thesummarised geotechnical properties given in Formation (see Tables 4- 10). . tables. 4-22 areintended as ageneral guide to engineeringproperties of thematerials and their variation.In most cases, differencesbetween Engineering Geology of the Bedrock Formations maximum andminimum values are high. The (Rock) classification should only be used,therefore, as a As indicatedabove, geotechnical data available guide when planninga site-investigation and not from site-investigationreports for many as substitute a for sampling a and testing formationsare limited. This is particularlytrue Deeside (North Wales) Thematic Geological Mapping 39 of the solid formations.In many cases no test Measures, HalkynFormation and Minera results areavailable and consequently there is only Formation. brief descriptive information. 4. Mixed Limestone/Sandstone/Siltstone The bedrockformations of thearea are defined Dolomitic and argillaceous limestone and . on the basis of internal lithological characteristics. calcareous sandstonesand siltstones of the Theyeach comprise rocks of broadly similar Minera and Foe1 formations. engineeringcharacteristics, these arebroadly as 5. Mudstones/Shales related to lithology. It should be noted however, i) Purplishgrey and reddishbrown mudstones that the formations take account of the degree no of the Ruabon Marl. andnature of fracturingwhich can greatly ii)Purple, reddish brown, yellow andgrey, influenceengineering behaviour. Thebroad mottled,silty mudstones and seatearths of lithological divisions used below areset out in the Buckley Formation. terms of decreasingstrength but, again, this is a iii) Grey mudstones/shales and silty mudstones generalisation. The divisions almost equate to of theProductive Coal Measures and the those shown onThematic Element, Map 1 - Halkyn Formation. Bedrock Geology, exceptthat the Ruabon Marl Grey,iv) laminated, often cleaved, silty has been divided into sandstones and siltstones on mudstones of the Elwy Group. the one handand mudstones and shales on the other;feldspathic sandstones of the Productive Geotechnical data for these rock formations are so Coal Measures and theHalkyn Formation have sparse thata summary table of propertiescannot been grouped with the quartzitic sandstones of the be presented,However, where appropriate, such Halkyn and Mineraformations. This has been summarydata as areavailable are given. For done because onlylimited data are available for fuller descriptions of the formations, see Summary these rocks. of Geology. The groupings are: I. Limestones 1. Limestones variousThe limestone formations of the i) Darki) grey, thinly bedded, argillaceous Carboniferousoccur on the sparsely populated limestones with mudstones and western side of the study area. Little geotechnical interbedded, pale grey, massive, shelly data are available, andthere is only one limestones of theCefn Mawr Limestone site-investigationreport which attempts to and Minera Formation. describe the limestones. ii) Pale grey,coarse-grained, rubbly, shelly limestones of the Loggerheads Limestone Limestones I (i) (Cefn Mawr Limestone and and the Llanarmon Limestone. Minera Formation) and iii) Dark,iii) brownish grey, porcellanous Limestones I (ii) (Loggerheads Limestone and limestones withsubordinate fine- to Llanarmon Limestone) coarse-grained,shelly limestones of the Forengineering purposes no differentiation Leete Limestone. between these two groups has been made because of lack of data. 2. Chert Greyand white, laminated and glassy cherts The limestones arestrong but mass strength will and siliceous mudstones of the Halkyn be dependent on the presence of mudstone/shale Formation. layers, their thickness andseparation, and jointing.The degree of jointing is variable. 3. Sandstones Open or infilledcavities and swallow holes (see i) Brownish andred yellow, fine- to Description of ThematicElement, Maps 2 and 5 medium-grained sandstones of the for descriptions of infillingdeposits) clearly Kinnerton Sandstone Formation. presentan engineering hazard. In thestudy area ii)Purplish grey sandstones, weathering to a such features as have been observed are generally dense or very dense sand, and siltstones of of small size though some substantial areas of the Ruabon Marl. founderedground occur (see ThematicElement, iii) Yellowish brown to grey and white, fine- Map 2). Larger cave systems are known to coarse-grainedfeldspathic, quartzitic elsewhere inthe Carboniferous limestones of the (variably calcareous lower in the sequence) Vale of Clwyd. sandstones of Productivethe Coal 40 Deeside (NorthWales) ThematicGeological Mapping

The limestone rockhead is veryirregular with siltstones. weathering opening up joints into which overlying Maximum nettsafebearing pressures for superficialdeposits are washed down. Because of moderately strong sandstone ranging from 500 kPa the greater openness of near surface fractures and for shallow foundationsto 1500 kPa for pile theirgreater frequency it is possible that foundationshave been quoted for sandstones in limestones withinabout 5 m of rockheadcan be theFlint area, whilst values of around 2000 kPa rippedwithout blasting. Inthe more massive for piled foundationshave been suggested limestone however, blasting will be necessary. between Flintand Connah’s Quay. If this Cuttings in shaly limestones with mudstone layers sandstone is used as a pile foundationin the shouldnot be steeper than 1:l as weathering of vicinity of the Dee Estuary, any concrete for cast shaly layers may lead theirto erosion and in situ piles will have to be placed beneath water subsequent loss of support to limestone blocks. which, in some instances, maybe saline. Care The limestone wouldbe suitable for use as a fill shouldbe taken to determinethe nature of the material after breaking up and can be classified as strata below the pile founding depth to avoid the arock for compaction purposes. Theproportion possibility of over-stressing anyunderlying of mudstonelshale is probablyinsufficient to weaker mudstones or shales. affect the quality of the limestone fill. The sandstone will bedifficult to excavate by Limestone I (iii) (Leete Formation) digging and will probably,therefore, require No engineering information is available. ripping. Sandstones 3 (iii) the Productive Coal 2. Chert (in Measures, the Halkyn Formation and the Minera Thecherts are variously described as strong, Formation) massive, very brittle, highly jointed rockwith These sandstones includethe Hollin Rockand near surface joints that are open and clay infilled. GwespyrSandstone (see Summary of Geology). Laminae of fine-grained,cherty sandstone or Theyare variable but are generally moderately

~ . mudstonehave also been noted. Thereare no strong to strongand slightly moderatelyto geotechnical data available for the cherts. weathered;however, near rockhead, they may be weatheredto a weak rock and heavily fissured 3. Sandstones with clay infilling the fissures. Sandstones 3 (i) (KinnertonSandstone There is little geotechnical data available for this Formation) grouping. Maximum nettsafe bearing pressures Geotechnicaldata for this sandstone areonly forfootings on moderatelystrong sandstone available from beneath the alluvial deposits of the beneath the weathering zone havebeen estimated Dee Estuary, where a maximum of 9.5 m has been at between 1000 and 3000kPa. S.P.T. results for penetrated.The sandstone is generally highly to the sandstones gave N values in excess of 50 for a moderatelyweathered (the weathering full 450 mm test drive for slightly to moderately classification is that described by Anon (1972)) in weatheredrock and between 25 and 47 for ?4 the 2 to 3 m belowrockhead, becoming slightly completely weathered rock. weatheredbelow thatdepth. Fractures (from Forthe more massive, strong sandstones in this R.Q.D. andfracture space index records) range group, explosives will be required to break up the froma very low spacing (6-20 mm) within 2 to rock to facilitate excavation. Weathered sandstone 3 m of rockhead to a high (200-1000 mm) spacing near to rockhead may be ripped or dug. at greater depths. Sandstones 3 (ii) (Ruabon Marl) 4. Mixed Limestone/Sandstone/Mudstone Valuesof uniaxial compressive strength are very (Minera Formation and Foe1 Formation) variable rangingfrom around 10 MPa to about No site-investigationencountered rocks of these 81 MPa witha mean of 5 1 MPa (16 tests). For formations,and hence no geotechnical dataare siltstones, in. the same sequence, the mean strength available. is 50 MPa withrangea from about 16.5 to 95 MPa (17 tests). Initialtangent modulus of 5. Mudstones/Shales elasticity values have also been determined. These are very variable ranging from 1.4 to8.3 GPa for Mudstones 5 (i) (Ruabon Marl) the sandstones andfrom 0.7 to 7 GPafor the Thesemudstones are difficult to distinguishfrom Deeside (North Wales) Thematic Geological Mapping 41 themudstones of the Buckley Formation (see upto 20°. A number of joint setshave been Summary of Geology). Littlegeotechnical data observed, theprincipal one being sub-vertical areavailable butit is anticipatedthat their withgenerally clean joints and occasional calcite geotechnical properties and engineering behaviour infilling.Subsidiary sets atabout 70' tothe will be similarto those of the mudstones of the horizontal and 45' have been noted. Buckley Formation. Unconfined compression tests The mudstones weatherresidualtoa soil or in slightly weathered mudstone and shale samples completelyweathered rock which is a firm to haveindicated strengths inthe range 16.5 to stiff, brown and grey,laminated, fissured, silty 18.6 MPa (14 samples), whilst initialtangent claywith litho-relicts of shale. The weathering elasticmoduli arein the range 0.7 to 2.3 GPa. zone has been observed up to about 4 m thick for Maximum nettsafe bearing pressures for large completely weatheredrock, butthe degree of spreadfootings have been estimated at 650 kPa. weathering will decreasebeneath this depth. Strength may be expected to increase with depth, Weathering is greater where drift cover is thin. depending upon the degree of fracturing. The slightlyweathered to highlyweathered Mudstones 5 (ii) (BuckleyFormation) mudstonecan be classified a clay of Thesemudstones have beendescribed ranging as as intermediateplasticity (CI) (Figure 7) and low from a blocky, fractured shale with traces of clay compressibility. The completely weathered rock is weatheringto a stiff to verystiff silty clay with a clay of intermediate to high plasticity (CI to frequent litho-relicts in the top metre. CH)(Figure 7). Shear strengths for the highly to Geotechnical datafor the mudstones arelimited, completely weatheredmudstones range from butare summarised inTable 4 for thehighly to around 50 to about 200 kPa, but increasewith completely weathered mudstones upon which tests depthand decreasedweathering. Chemical tests have been carried out. Thisweathered zone indicate that pH ranges from 7.4 to 8.0 and that, varies inthickness, andup to 6 mhave been with the exception of onesample, sulphate recorded, though this should not be considered as determinations place the materials in class 1 of the a maximum. The weathered rock can be BRE classificiation (Building Research classified as a clay lowof intermediateto Establishment 1975) so that no special precautions plasticity (CL to CI) (Figure 7) and low need to be takenover theconcrete used (but see compressibilitywith amedium to high rate of the comment under Fill and Made Ground below). consolidation. Strengthdeterminations indicate For all degrees of weathering, N values from the thatthe clay is firmto stiff but, because of the S.P.T. are generally greaterthan 50, though fracturednature of the material it has been occasional lower values have been obtained difficultto sampleand, therefore, the clay is indicating local softening of the weathered clays. probably very stiff en masse with shear strengths The mudstones/shales have not been considered probably greater than 500 kPa. suitable as fill materials unless there is no For pile foundations which may be considered for alternative; then they should only be used for low sites along the Dee Estuary, allowable end bearing embankments.The weathered clay tends tobe pressure of about 200 kPa may be assumed with too wet and the mudstones/shales have a tendency allowable shaft resistancein the mudstones of to weatherrapidly, swell and settle. However, around 150 kPa. Piles should be taken 3 minto their swelling has not been quantified. therock through the weathered zone. N values Side slopes for cutshave been recommendedat fromthe S.P.T. arein excess of 50, evenin the 1V4H withdrainage, particularly where the weathered zone. groundwater table is high. As observed above, Mudstones 5 (iii) (Productive Coal Measures precautions may have to be taken to prevent and HalkynFormation) weathering and swelling. Geotechnically these mudstones are very similar Landslipshave been observed at a few locations, 5-10), thoughdata for those of the (Tables particularlyaround Holywell (see Thematic Productive Coal Measures are more limited. Element,Map 2 Superficial(Unconsolidated) Consequently, the mudstones/shales are considered - deposits and itsdescription). The failure planes one unit geotechnically. They are weak or very as for these slips appear to be located in weathered weak to moderatelystrong or strong,jointed mudstone/shale.For stability analysis at one site shales and mudstones. Strength decreases with the following parameters were selected: peak increasedweathering. Theinternal laminae effectivestrength parameters c- = 15 kPa, generally dipat low angles, from sub-horizontal - 42 Deeside (North Wales) Thematic Geological Mapping

cv

...... CH ...... /......

CI ME

CL nv ...... ',

lob SF

0 u10 20 40 70 100 110 120 0 30 50 60 80 90 Liquid Limit %

Buckley Formation - highly to completely weathered

Slightly to highly weathered J

Figure 7 Plasticity Diagram for Weathered Mudstones and Shales Table 4 Summary geotechnical data for Mudstones of Buckley Formation (Highly to Co~nple~elyWeathered)

MoisturP Liquid P1asti.c Specj f j c N-value Content Limj t Ljmj t Dens 3' ty Gravi ty GravelClay Sand Silt % % % Mg/m % .x % x 10 14 l1 11 15 Mudstones of Buckley . 11 Formation - highly to completely All> 50 lO(2.8) 37(7.4) 18(2.5) lg(5.8) 2.28(0.07) Weathered.

5-16 2447 15-22 9-25 2.20-2.43

FILE FORMAT

No. of Optimum samples ty Maximum ivloisture so3+ CBR Dry Den 3yit Content Comments Average(Standard Mg/m x % Deviation)* Weathered zone observed toup 6m thick. Low compressibility, Range medium to high rateof consol- idation. Firm to stiff or very stiff. Piles require 3m pene- tration intorock, through weathered zone. I I I I 1

I .. Plasticity SO in soil Description of Index Total 2% water In 2 Mv 2cv I I I Class ' Cornpressi bility m /MN Examples Class m /year Range Soil Type CLAYS 5 ' Very high 1.5 Very organicalluvial above 1 40.1 Greater clays and peats Montmorillonite than 0.3 - 1.5 Normallyconsolidated High plasticity HI. gh 2 0.1 1' 25 alluvialclays, eg. - partsin estuarineclays - 100 000 1-10 125-5 lkledjum plasticitJ bk. d i urn 0.1 - 0.3 Fluvjo-glacialclays '3 I Lateclays 1 partsin -. litre 100 000 LO\% 0.05- 0.1 BoulderClays 4 1.0-2.0% 3.1 - 5.6250-500 Very low below 0.05 Heavi ly overconsoljd- grams/ partsin atedBoulder Clays. ljtre 100 000 Stiff weathered rocks 5 >2.0% 5.6 500 parts After iie.ld (l9t32) After Larnbe and Whitman (1979) grams/ in 100 000 1 j tre i COEFFICIENT OFVOLUME COMPRESSIBILITY Mv COEFFICIENT OFCONSOLIDATION Cv After.Bui1dingResearch Establishment (1975)

SULPHATES IN SOILS AND GROUNDWATERS Table 5 Summary geotechnical data for Shales/Mudstones of Productive Coal Measures (Fresh to Slightly Weathered)

Moisture Lj qui d Plastic Plastici ty Bulk Dry Spec i f i c Content Limi t Ljmi t Index Gravi ty Silt Gravel Density Dens'ty3 Clay Sand % % % % Mg/m Mg/ m % % % % I I 5 4 1 Shales/Mudstonesof ProductiveCoal Measures;fresh to ~11250 slightly weathered.

- 2.29 1 I 2-8

FILE FORMAT _. ndrained Opt 1 mum samples ohesion ibloisture p~ so3+ CBR Content Comments Average(Standard kPa % % Deviatj on)* 1 9 9 Shear strength increases with Range depth and decreasing weathering Unsuitable as fill material. quotedwhere no. 1 Side slopes 1:4 with drainage. Landslippingpossible, slopes of samples 2 10 + classvalues >To at particular risk.Piles seerelevant require to be taken through tebles beiow 100 7.4-8.0 weatheredzone.

?lasticity SO in soil Dtscri.ption of Mv Index Total 23 water In Class Compressibility m2/MN Examples Range Soj 1 Type 'lass extract Groundwater SOg CLAYS 5 Veryhigh above 1.5 Very organic alluvial Greater 30 parts claysand peats Montmorillonite 1 ((0.2% I than I in 100 000 I 4 High 0.3 - 1.5 Normallyconsolidated 25 High plasticity 30 120 alluvialclays, eg. - 3 0..1-10 1 - 1, I partsin estuari ne clays fI 25 5 Wedium plasti ci t 3 Medium 0.1 - 0.3 Fluvio-glacialclays - 3 Lateclays I 0.5-1.0% 1.9 - 3.1 120-150 grams/ partsin 2 Low 0.11 0.05- BoulderClays 15 or Less 1 Low plasticity litre 100 000 4 3.1 - 5.6 1.0-2.0%250-500 below0.05 lieavilyoverconsolid- grams/ partsin atedBoulder Clays. ljtre 100 000 Stiffweathered rocks iII 5 >2.0% 5.6 500 parts After Head (l982) After Larnbe and Whi tman (1979) grams/ i n 100 000 1i tre COijFFICIENT OF VOLIJME COMPRESSIBILITY Mv COEFFICIENT OFCONSOLIDATION Cv Aftec.Bui1dingResearch Establishment (1975) .

SULPHATES IN SOILS AND GROUNDWATERS Table 6 Su~nmarygeotechnical data for Shales/Mudstones of Productive Coal Measures (Moderately to Highly Weathered) r------~- - ,- C,~otrci~n~ Croupcal Clay Silt Sand Gravel I % % IO %

Shales/Mudstones of productj.veCoal Measures; rnoder- ately to highly weathesed.

____-FILE FORMAT

No. of Opt j mum s amp I c s Maxi mum i*loisture pti so3+ CBR 1 Dry Den 3 i ty Concent Comments Average(Standard Mg/m % Deviation) * Shear strength increases with Range depth and decreasing weathering Unsuitable as fill material. * quotedwhere no. Side slopes 1:4 with drainage. of samples > 10 + class values see rei evant I I require to be takenthrough --______tehles beiow weatheredzone.

SO soil r. Plasticity in Dlscriptj on of Mv Index 2cv 1 Total I 2% water 1 In Class Compressi bility m2/MN Examples lass m /year Range Soj 1 Type '1as SOg extract Groundwater

5 Very high above 1.5 Very organic alluvial CLAYS I 30 parts claysand peats Montmorillonite in 100 000 POe2* I 4 0.3 - 1.5 Nornrallyconsolidated High plasticity High 120 alluvialclays, eg. 2 0.2-0.5% 30 - partsjn estuarjneclays -- 100 000 1-10 25-5 Medium plastj cj t I 3 Ned~um 0.1 - 0.3 Fluvio-glacialclays Late clays 3 '0.5-1.0% 1.9 - 3.1 120- 150 I grams / partsin 1i tre 100 000 j 2 Low 1 0.05- 0.1 BoulderClays 1 ascicj ty 1 I I I I I SILTS 4 1.0-2.0% 3.1 - 5.6 250-500 1 very low below 0.05 Heavilyoverconsolid- I grams/ partsin ated BoulderClays. 5 1 >loo ljtre 100 000 Stiffweathered rocks I I . 5 >2.0% 5.6 500 parts After iiead (l9E!2) After Lambe and Whi trnan (1979) grams/ i n 100 000 litre COEFFICIENTOF VOLUME COMPRESSIBILITY Mv COEFFICIENT OFCONSOLIDATION Cv \fter.BuildingResearch Establishment :1975) .

SULPHATES IN SOILS AND GROUNDWATERS 46 Deeside (North Wales) ThematicGeological Mapping

" a; a* c

v1 '(3 c, f# 9)

v) E

U +m0 [/I i*

.n a3 a;. 0 T-I

31

In (r mlo I If

m

m rl E" X w

ln 0 rl v) 0 rl 0 0 2 Ul >= e x4 9) I I m (v m 0 d I D 9 z 0 0

c M n I m T Deeside (North Wales) Thematic Geological Mapping 47

I I I L 0 ?-4 c, 070 ai m uo 3L a8 G'CI mo HE: u 3 00 P " 5

a -ae IpIH V0

a 4. I O 0 X UI

X P

U +L >>, N' N'

I;

(3 8 A I d z rl 4 48 Deeside(North Wales) ThematicGeological Mapping

L c, ai 3 mM ca WE: U rl 0 0 mc u .n I m c, I ----I-- ai E V c, 4 .- ap m rl

I t/cu h w 0 cu m 0 -8 V V

+ 4 m 0 (u m

4

X d a R m I .,-I v! a3 d x4$0

012I 0I

m4 cum

J a. LC, 3c UP;myap 0 xu U 3

dA d I

k * n+-' 1 Table 10 Summary geotechnical data for Shales of Halkyn Formation (Completely Weatherd to Residual Soil)

Moisture, Ljquid Plastic Plasticity Bulk D rY Specific Gt>oteclrlij cal Group N-val UP Content Li mi t Li mi t Index Dens'ty3 Dens'ty Clay GravitySilt Sand Gravel % % % % Mg/m Mg/m % % % % 30 24 15 15 15 12 1 Shales of ilalkyn Formation ( Holywell cowletely 23 values 26(11.0) 23(4.0) 49(12.4) 1.96(0.00) 27(11.2) weathered to 50 residualsoil. 8- 50 749 12-53 17-32 32-77 1.47 1.84-2.11

FILE FORBAT

I No. of Undrained Angleof Opt j mum samples Cohesj on Internal Mv* CV' Permeabi-lity Maximum irloisture pH CBR so3+ Comments Frj ctjon Dry Den 3 i ty ConLent Average(Standard kPa (") rn2/MN m2/yr m/s Mg/m % % Deviation)* 12 12 3 3 Completelyweathered zone Range observed to &.Strength increa- 1 ses with depth and decreasing * quotedwhere no. 92(53) 1 weathering.Unsuitable as fill of samples 2 10 Landslipping possible particul- + classvalues arly for slopes >7°.Piles need see rei evant to be taken through weathered 23-198 0 '7.6-7.7 zone.Cut slopes 1:4 with drain- tebl es Leiow-- ape.

? 1 SO insoil Drscriptj on of Mv Index Total 23 water In Class Compressibility m2/MN Examples Class m /year Range Soil Type Class extract Groundwater SO3 CLAYS Very organic alluvial 1 30 parts claysand peats Montmorillonite 1 (0.2% I Pry high in100 000 4 0.3 1.5 Normallyconsolidated plasticity High - 2 High 2 0.2-0.5% 30 120 alluvialclays, eg. - 0-.1 1' 25than partsjn estuarine clays - I 100 000 II 3 1 - 10125 - 5 3 kdiurn 0.1 - 0.3 Fluvio-glacialclays 120-1 50 Lateclays 1 partsin 4 100 litrej 15 tyless Lowci plasti 100 000 2 Low 0.05- 0.1 BoulderClays 10 - or 1 2 50- 500 1 Verylow below 0.05 Heavi ly overconsoljd- partsin atedBoulder Clays. 5 >loo j 100 000 Stiff weathered rocks 500 parts After Head Q982) After .ambe and Whj tman (1979) grams/ jn 100 000 i ljtre COEFFICIENT OF VOLUME COMPRESSIBILITY Mv COEFFICIENTCONSOLIDATION OF Cv AftecIBuildingResearch Establishment

(1975)~

SULPHATES IN SOILS AND GROUNDWATERS 50 Deeside (North Wales) ThematicGeological Mapping

4- = 21'; residualeffective strength parameters - The engineering problems associated with each of c- = 0 kPa, 4- = 14O; bulkdensity 2.00 Mg/m3. these depositsarereviewed following their Where slopes steeper than about 7O are present on descriptions. Theirdistribution is shownon these mudstones/shales, carefulinvestigation ThematicElement, Map2 Superficial shouldbe made to try to determine if any slope - (Unconsolidated) deposits. movement has taken place and to check the effect of any proposed structure upon slope stability. 1. Backfill and Made Ground Limitedinformation is available onbearing This category is veryvariable in composition, pressures forthe mudstones/shales. Forthe thickness and geotechnical properties. In general, completelyweathered rock, maximumnett safe it is loose, weak, and highly compressible. The bearing pressures of 120 kPafor strip footings most common materials involved are chemical and 145 kPa forsquare footings havebeen waste, domesticrefuse, mining waste and suggested. moderatelyweathered For quarrying waste. mudstones/shales, values inthe range 300 to 600 kPa are proposed; for slightly weathered 2. Peat mudstones/shales, 1200 to 1600kPa. Forend bearing piles, end bearing pressures between 1000 Geotechnicaldata (Table 11) on peat are only and 1500 kPa are suggested, and usually towards available forthree samples, thoughit was thehigher end of the range. The piles should be encounteredseveral in boreholes (around taken through the weathered zone (at least 2.0 m, Penyffordd,Northop, Holywell andFlint). These butdependent on the site)into the hard occurrences of peat were at,or near, theground mudstone/shalebeneath, possible. if surface(except in one case whereit was buried Confirmationshould be obtained that weathered beneath 6.5 m of fill)and it was recorded as mudstone/shale horizons arenot present within varying in thickness from about 1 m up to almost the stressed zone beneath the piles. 3 m. It is usually associated withvery soft, grey, organic, alluvial clays and is, itself, usually very As these mudstones/shales soften on contact with soft to soft,dark brown to black andfibrous, 'water, excavations should be protected as far as is thoughoften it has asignificant clay content. possible against wetting, andthey will need Occasionally, sandy bands are found in it. support.The weathered mudstones/shales are diggable but may need ripping when fresh. The peat is highly compressible withhigh moisturecontents and Atterberg limits, and low Mudstones 5 (iv) (Elwy Group) density. It will not necessarily be presentat the No geotechnical dataare available. forthe surfacebut maybe thinly covered by alluvial mudstones of this group. Theyare often cleaved sands or clays. (see Summary of Geology). 3. Wind-blown Sand Engineering Geology of the Superficial (Unconsolidated) Deposits (Soils) As thisdeposit was notrecorded anyin site-investigationreport, no geotechnical data are Thesuperficial (unconsolidated) deposits have available. The sand is generally fine-grained. beensubdivided both onthe basisof their lithology (whichcan be directlyrelated to their 4. Alluvium engineeringcharacteristics) and the environment in whichthey were deposited. The following Mainly restricted to the floor of the valley of the categories of depositare described in terms of and several smaller river valleys in the their engineering characteristics. alluviumarea,the varies soft,from a compressible, silty clay or clayey siltof low to 1. Backfill and Made Ground intermediate plasticity (CL to CI)(Figure 8) to a 2. Peat clayey, silty, fine-grained sand, with occasional 3. Wind-blown Sand gravel. The geotechnical properties of the 4. Alluvium alluvium are summarisedin Tables 12 and 13. In 5. Estuarine Alluvium most respects it resembles estuarinealluvium (see Lacustrine Alluvium 6. below)but with a greaterabundance of gravel, 7. Heterogeneous deposits (Head) andgreater heterogeneity produced by the more 8. Glacial Sand and Gravel energeticdepositional environment. Generally 9. Till (Boulder Clay) low maximumnett bearing pressures havebeen Table 11 Sunlmary geotechnical data for Peat

Plastjci ty Ceotect-lnjcal Group N-val Index % x 1 1 Peat; dark brown, fibrous,with occasional sand or clay. I 4 233 1 FILE FORMAT , No. of ndrai ned Optj mum samples ohesi on Woisture PH Con cen t Comments Average(Standard x Deviation) * 1 Very soft, highly compressible Range lto 3m thickness recorded. I * quotedwhere no. of samples > 10 + class values seerelevant 1 9-32

I 1 I I SO insoil Description of Index I Total I 2% water I In Clysi Compressi bility 1 rn2/MiN 1 Examples Soil Type 'lasd SOg 1 extract I Groundwater I CLAYS Very highabove 1.5 Vewy organicalluvial - 1 (0.2% 30 parts clays and peats Montmorillonite in, 100 000 High plasticity 2 0.2-0.5% 2 30 120 alluvialclays, eg. - parts in estuarjne clays 100 000 Medj um plasti cj t Late clays parts in Low plasticj ty litre 100 000 10 - 100 15 or less 1 I I I SILTS 1 Verylow Heavi.1~ overconsolid- parts in atedBoulder Clays. 2 litre 100 000 Stiff weathered rocks 5 >2.0% 5.6 500 parts After i-lead 0982) After Lambe and Whitman (1979) grams/ jn 100 000 1i tre COEFFICIENT OF VOLUME COMPRESSlBILITY Mv COEFFICIENT OF CONSOLIDATIONCv \fter. Building Research Establishment

(1975)~

SULPHATES IN SOILS AND GROUNDWATERS 52 Deeside (North Wales) ThematicGeological Mapping

CH / / CL MV

0 LJLLU I-L 0 10 20 30 40 50 60 70 80 90120 110 100 Liquid Limit %

Alluvium - Clay

F]Estuarine Alluvium - Clay

Figure 8 Plasticity Diagram for Head, Alluvial and Esturine Alluvial Cohesive Soils Deeside (North Wales) Thematic Geological Mapping 53

I L 0 aJ (00 4 u uo aJ CL 5" 0-0 mo ca 0.0 zap ne 5:,8 ff tu orl 0 OLO oc mmo 0.- u (\I 0.4 asap I v) T--

T-om x 4% 0- V

t I rl 1

Nrl

z-l K/ .rF) rnE hC5\ LaJM oaz

n Nn m m N XUI rl -I- p.mL a

cv

a; A 0 d " m $ I as 3 z co I

P Table 1.3 Surnmary geotechnical data for Alluvium (mainly clayey, silty fine sand) CII A

Moisture Liquid Plastic Plasticity Bulk Spec i f i c Li mi t LI t Index C1 ay Si It Gravel Sand Content mi Density % x % % Mg/m 06 % % %

A1luviule , mainly clayey, si-lty

4

1745

FILE F0RIdAT

No. of ndraj ned Angleof Opti mum samples CV' Permeabi 1i th Maxi mum idoisture PH FrS cti on Dry Dengi ty Conrent Comments Average(Standard Ioh:Xon rn2/yr m/s Mg/m % Deviation)* Very heterogeneous. Low nett i bearing capacities, unsuitable i Range for support of lightweight : structures,though gravelly * quotedwhere no. layers show much higher bearin4 of samples 2 10 capacities. I! + classvalues

~ 65-119

.- ~lasttcity Description of Index I 2cv Compressj bility1 m2yiI I Examples "uass m /year Range Soil Type CLAYS Very high 1 40.1 Greater 30 parts clays and peats Montmorillonite than in 100 000 High plasticity 2 9.1 - 1. 25 alluvi a1 clays, eg. 30 - 120 estuari ne clays 11 :Vledi um plastj cit Fluvio-glacialclays Late clays Low plasti ci ty 0.05- 0.1 BoulderClays I I Lsw I I SILTS 4 1.0-2.0% 3.1 - 5.6 250-500 Verylow below 0.05 Heavj ly overconsolid- grams/ partsin atedBoulder Clays. litre 100 000 l/. Stiff weathered rocks I J 5 >2.0% 5.6 500 parts After Head (1982 ) After Lamba and Whi tman (1979) grams/ in 100 000 1i tre COEFFICIENT OFVOLUME COMPRESSIBILITY Mv COEFFICIENT OF CONSOLIDATIONCv After. Bui 1 ding Research Estzblishment

(1975)~

SULPfiATES IN SOILS AND GROUNDWATERS Deeside (North Wales) Thematic Geological Mapping 55 quoted,though gravelly layers showmuch higher hillcreep. Typically,the material is asandy, silty bearingpressures (100 kPa for foundations 1.2 m clay with occasional gravel. The composition is wide, reducingto 80 kPa for foundationsgreater very muchcontrolled by thenature of the soils than 3 m wide). Sulphate contents are not high. and rocks immediately up-slope. For example, southeast of Holywell, the head consists of 5. EstuarineAlluvium completelyweathered mudstone with a large proportion of freshand slightlyweathered These depositsoccur thein Dee Estuary mudstonefragments and occasional roundedgrey (includingthose below the highwater mark). limestone gravel. Thisoriginates fromthe Three lithologicalunitsshowing distinctive mudstones of theHalkyn Formation andthe geotechnical properties were identified in borehole Carboniferous limestones of the area. The soil is logs: stiff to very stiff. i) Alluvial clay: very soft to soft, occasionally Head does not necessarily occur at the surface. It firm,grey and brown, occasionally sandy, may underlie(boulderthetill clay). The siltyclay with sandy and organic layers. thickness of the head is veryvariable, ranging The deposit reaches 3 m in thickness, is of from less than 1 m up to at least 5 m. low to intermediateplasticity (CL to CI) (Figure 8), normally consolidated and isof Geotechnicaldata on head arelimited, being high compressibility and low strength. restrictedaroundsites to Holywell and ii) Clayey, silty,fine-grained sandan Penyffordd. However, it is muchmore extensive uncommon lithology, intercalatedwith the than shown on ThematicElement, Map 2, which alluvial clay and alluvial sand. shows head only where greater than 1 metre thick. iii) Alluvial sand: grey, brown and Its geotechnicalproperties are summarisedin grey/brown,uniformly graded, slightly Table 18. siltysand, commonly with sea-shells and The more cohesive head can be described as a soft occasional gravel. Generallysaturated, to firm clay andsilt of low to intermediateand loose but becoming denser with depth, sometimes highplasticity (CL to CI and ML' to reaching medium dense at about 10 m. MI and MH) (Figure 8) andmedium to high Thegeotechnical properties are summarised in compressibility. S.P.T. N values areextremely Tables 14-16. variable,probably reflecting the heterogeneous nature of the deposit. A broad trend of coarsening with depth and away fromthe estuarymargins is paralleled by 8. Glacial Sandand Gravel increasing N values fromthe S.P.T., and decreasingmoisture contents. This trend is a This is a widely occurringand locally thick regional one, thoughon a site scale the different deposit, found at surface as well as within the till. lithologies are intercalated. It is avery variable, heterogeneous deposit; the material is in general,medium dense and well 6. LacustrineAlluvium sorted. The main lithology is a well-sorted sand This lithology occursonly locally. It consists and gravel, withseveral subordinate lithologies. mainly of asoft to stiff, laminated, compressible Clay canoccur as a soft to firm matrix withthe clay of lowto high plasticity (CL to CH) (Figure granularmaterial but more commonly formsthin 9), or asoft to stiff, gravel-free, compressible bands which canvary from very weak to very clay of low to high plasticity associated with stiff. Loose gravelly or sandysilt layers, and glacial till. Thelimited geotechnical data lenses of siltysand are also found.Geotechnical available are summarised in Table 17.S.P.T. properties are summarised in Table 19. resultsshould be interpreted with caution (see In some areas,stratified medium dense to dense, Engineering Problems below). occasionally loose silty to verysilty sand and subordinategravel occurs. .Thegeotechnical 7. Heterogeneous deposits (Head) properties of these sandssummarisedare Head deposits are heterogeneous and are found as separately in Table 20. a relatively thin veneer on many hillslopes, minor valley sides and valley bottoms. Theyare 9. Till (Boulder Clay) transporteddeposits formed by solifluction (in This is often a very thick and widespread deposit glacial andimmediately post-glacial times) and occupying,together with glacial sandand gravel, 56 Deeside (North Wales) ThematicGeological Mapping

CH

CI ......

MV

- MH - 10 - sc ...... - ...... : ...... M L 0 1111 IIII IS81 IIII l!Il IIII Ill1 0 10 20 30 40 50 60 70 80 90 100 110 120 Liquid Limit %

Till (Boulder Clay)

FlLacustrine Alluvium

Figure 9 Plasticity Diagram for Till (Boulder Clay) and other Glacial Cohesive Soils Deeside (North Wales) Thematic Geological Mapping 57

+ m 0 m

X a

3

-

? (3

m rl a m w

7-1 C I 3

3 x >li 58 Deeside (North Wales) ThematicGeological Mapping

-- 9 ffl '2wf C, (D 4 a E u.

p: I I I a-

+ m rn0

N u)

lo, X PI 4 +L >A v\ m N +3 >\ T EN (0 s 0

(0 2 d

ffl CUP; 'p 04 am .E Ppa om c- Zffl mc uo.,-4 -4 m Table 16 Summarygeotechnical data for EsturineAlluviuml(Sand)

Geotechnj cal Group N-Val ue % -~ EstuarineAlluvium; 549 3a 1 alluvial sand with or wi-thout she1 Is, 21(5.6) no significant gravel.

6-120 5-38 35

FILE FORMAT

No. of Indrained Angle of samples lohesion Cv' Pernleab i. 1i ty Maxj mum Concen t SO3+ 1 CBR 1 FrS c tion Dry Den3j ty Comments Avel,age (Standard kPa 2 '7 nl /yr m/s Mg/m Deviation)" 5 51 Range

quoted where no. 2 of samples > 10 need shoring and de-watering. + class values Bearingcapacities increase 1 'with depth. SPT unreliable due 3-30 0-34 I 5-45 /to'blowing' in sands. CBR la. I b-2-9-2 .- Plasticity SO in soil Description of Index Total waterIn 2cv 23. Examples Class in /year Soil Type :lass extractGroundwater Range SOg Very above1.5high Very0rganj.c alluvial 1 40.1 Greater CLAYS (0.2% 30 parts clays and peats Montmorillonite 1 than in 100 000 0.3 - 1.5 Normallyconsolidated High plasticity 2 25 2 30 alluvialclays, eg. 0.1 - 1' 0.2-0.5% - 120 parts estuarineclays jn 109 000 ~~ 1Fluvio-glacialclays 1-10 ,25-5 Medium plastici t 1.9 3.1 Lateclays - 120-150 I' grams/ j parts in 11 tre 000 1 0.05- 0.1 I BoulderClays I SILTS Very low below 0.05 Heavi-ly ovcrconsoli d- atedBoulder Clays. 5 > 100 Stj ff weathered rocks 1 500 parts u_After Head (1982 ) After Lambe and Whi tman ( 1979) grams/ in 100 000 1 i tre COEFFICIENT OF VOLUME COMPHESSlUILITY Mv COEFFICIENT OF CONSOLIDATION Cv Aftec.BuildingResearch Estz5lishment (1975)

SULPHWTES IN SOILS AND GROUNIIWATS P

Table 17 Summary geotechnical data for LacustrineAlluvium

Mol sture Liquid Plastic Plasticity Bu 1I; Gpotecllni cal Group Content N-valueLimit Limit Index Density % % % Mg/m

10 53 24 24 4 LacustrineAlluvium; 4 soft to stiff, lam- j-nated,compressible clay. 40(23.5) 18(5.1) 34(9.1) 17(2.7) 17(7.7) 2.09(0.11)

10-60 10-34 21-54 14-24 6-34 1.90-2.35 1.64-2.04 2 L FILE FOWAT N

Jndrained Angle of Op timum Internal CohesionMv+ Cv+ Permeabj lity Maximum lbloisture pH so3+ samples Frictj on Dry Den 3 ity Content Comments r-7kPa (0) m2/w m2/yr m/s Mg/m % Devi &Lion)* I t Problems of stability and 32 32 9 9 7 7 settlement, mainly in softer clays,the presence of which i! should be assumed rather than 80(46.6) 5(8.6) 1 2,3 3,4 considered as an exception when this deposit is identified. see rtievant 0-32 5.6-8.2 tebles beiow I 20-140

1 I 1 .- Plasticity SO in soil Uescription of Index Total 2% water In 2cv I I I I Compressibility1 m2:k I Examples Class m /year Range Soil Type extract Groundwater I I SO3 I I CLAYS above 1.5 Veryorganic alluvial 1 LO. 1 Greater - 1 30 parts Montmorillonite 1 1<0.2% lVery high I peats Iandclays than 1 I in 100 000 1 4 Normallyconsolidated High plasticity IIigh 2 9.1 25 2 0.2-0.5% 30 - 120 alluvialclays, eg. - 1' partsin estuarj ne clays I 1 100 000 3 1 - 10 \25 5 lvledium plastici t 0.1 - 0.3 Fluvio-glacialclays - 1 i Lateclays i 4 10 100 15 or less plasticity 0.05- 0.1 BoulderClays - 1 Low 1 I JI I I SILTS 1 Verylow below 0.05 Heavj ly overconsoli d- I grams/ atedBoulder Clays. 5 Stiff weathered rocks 1 500 parts After itcad 0982) After .ambe and Whj tman (1979) grams/in 100 000 ljtre COEFFICIENT OF VOLUME COMPRESSIBILITY Mv COEFFICIENT OF CONSOLIDATIONCv Aftec.BuildingResearch Estzbl~shment (1975) .

SIJLPHATES IN SOILS AND GROUNDWATERS Table 18 Summary geotechical data for MetrogeneousDeposits (Head)

Mol stut-c Li qui d Plastic Dry Spec i f i 1: Content Li mi t Li mi t Index Dens' ty Gravi ty Si It Density Clay Gravel Sand 76 % % Mg/m Mg/m % % % % 100 68 63 2 8 13 13 13 13 Heterogeneous Deposj ts (liead 1 23( 15.5) 18(9.3) 29(8.1) lO(5.6) 13(5.3) 2.10(0.19) g(6.4) 41(23) 34(23.3)14(11.3]

8-72 18-67 1248 1-26 1.90-1.97 0-70 20-93 1-40 0-23 2.61-2.71 1 1.49-2.46 FILE FORMAT

1 1 I Angle nf Opt i mum samples ohesj on Intern21 Mv' Cv' Permeabi.lj.ty Maximum bloisture p~ SO; 1 CBR 1 I Fricti on Dry Den it Concent Comments 22 ?Iy I Average(Standard ( "1 n /MN m /yr m/s Mg/m % Deviati on) * 55 14 1 2 2 9 Range very extensive as 1 a thin veneer.Possible presence' 36(28.6) 4(6.7) 3.4 4 * quoted whPre no. of samples > 10 may reactivate,with sloping 1 + class values I sites particularly at risk. I Perched water and running con- 0-30 1.93-2.04 1:l-7.99-10 4.8-10. ditions in 'coarser horizons, I - Plasticity SO in soil Description of Index 2cv I Total I 23 water I In Class Compressibility 1 mzyiN 1 Examples lass m /year Range Soil Type klasd SO3 I extract I Groundwater CLAYS 5 Veryhigh Very organic al-luvial 1 40.1 Greater clays and peats Montmorillonite I than 4 High High plasticity 2 alluvialclays, eg. L estuarine clays I 100 000 3 1 - 10 125 - 5 Xedi urn plasti ci t Ii Late clays ! 120-150 I partsin 4 10 - 100 i 15 or less Lou plastjci ty litre 100 000

SILTS 2 50- 500 I grams/ partsin atedBoulder Clays. 5 >loo f litre 100 000 Stiffweathered rocks 500 parts After Head (1982 ) After Lambe and Whjtman (1973) grams/ in 100 000 1 j tre COEFFICIENTOF VOLUME COMPRESSIBILITY Mv COEFFICIENT OF CONSOLIDATIONCv After. Building Research Estzblishment

(1975) ~

SULPHATES IN SOILS AND CROUNDWATERS 62 Deeside (North Wales) ThematicGeological Mapping

-- - -I

a: c > .5 0 0 0 Nodo ms mo 5: m8 u lcr IU LO 0 LO 0 (do in (do 0 ad N ad

P msc v)

ae 9 0 h :s; N -8 c:$f V N Ycn 0 V -- I h I U 1 +m0 le : Is3 03

Q, u) 3s; us '4m

7 In iu m 4

D +& (u

Q

1 m I z

3 0 rl -. 2 0 P; -1 >

P rl Table 20 Summary geotechnical data forGlacial Sand/stratified

IMoi sturc Liquid Plastic 'lastici ty Bulk Dry Spec; fir N-value Con tent Li mj t Ljmi t :ndex Dens' ty Dens' ty Grav~ ty C1 ay Sj 1 t Sand Gr-ave'] C;?otechrli cal Group !! 3 % % % % Mg/m Mg/m % x % % ~. 4 3 3 6 1 22 22 22 22 Glacial Sand/Stra- 74 43 tified; silty sand with gravel and 25( 16.6) 16(6.4) 8(9) 13(15.6! 69(23) g(14.5) occasional clay.

0-47 3-81 340 20-29 12-14 12-15 1.98-2.22 1.72 0-35 29-100 0-62

FILE FORMAT ! I ndrainec ingle of Opt i mum sampl es ohesj on Cnternal cv+ Permeabj ljt! Maxi mum ivloisture pH :r-I cti on Dry Den gyit ConLent Comments kPa ("1 m2/yr m/s Mg/m % Deviation)* 4 3 9 9

* quoted where no. i of samples210 + class values iI see relevant I 10-323 0-3 1.84-1.98 10-11 (5.7-7.9 beiow teb1-s _____.-_

r I 1 I I -. Plasticity SO in soil Descriptionof Mv Index Total 23 water In 2cv I I bility m2/MN Examples :lass m /year Range Soil Type CLAYS above 1.5 Very organic alluvja1 1 40.1 Greater <0.2% 30 parts clays and peats Montmorj llonite than in 100 000 0.3 - 1.5 High plasticity 2 25 ).2-0.5% 30 120 alluvja1 clays, eg. 9.1 - 1- - estuarine clays I I 3 1 - 10 125 - 5 ibiedi um plastjcj ty; I 3 Mecllum 0.1 - 0.3 Fluvio-glacialclays 1.5-1.0% Late clays I 1 I Il- grams/ 4 10 - 100 115 or less Lov plasticity

L SILTS I4 I grams/ partsin ated BoulderClays. 5 Stiffweathered rocks - >loo i A5 500 parts t After Lambe and Whitman (1975) grams/ in 100 000 i 1 i tre COEFFICIENT OF CONSOI.IDATION Cv After. Bui 1 dingResearch Establishment (1975)

SULPHRTES IN SOILS AND GROUNDWATERS 64 Deeside (North Wales) ThematicGeological Mapping much of thearea to the southeast of the A548 sands and gravels (see ThematicElement, Map 2). It is dominantly 5. Heterogeneous i) Head a red-browna todark brown, and occasionally deposits ii) Alluvial clayey, grey, silty and sandy clay with coarse-, medium- silty, fine-grained and fine-grained gravel and cobbles and boulders. sands This clay has low to intermediate and occasionally iii)Estuarine alluvial high plasticity (CL to CI and CH) (Figure 9) and clayey, silty, low tohigh compressibility. Subordinatebands fine-grained sands and lenses of sand or sandand gravel, and 6. OverconsolidatedGlacial till (boulder clay) occasionally firm to stiff, grey, laminated, sandy, cohesive soils silty, pebbly clay also occur, Generally, the till is 7. Densesands andGlaciali) sands and missivetowell-bedded, but occasionally it is gravels gravels laminated. A weatheredupper surface upto ii)Estuarine alluvial 2.5 thickm of orangeybrown andgrey, sands sometimesmottled, sandy clay with pebbles is The seven engineering groups correspond with the usually present, but mayabsentbe where fivegroups determined forthe purpose of alluvium overlies the till. Theweathered material assigning presumedbearing values in C.P. 2004 is softto stiff while the underlyingfresh glacial (British StandardsInstitution 1972) -except that till is generally stiff to hard. Granular materials here,the cohesive soil is dividedinto normally arevery loose to loose while the clayey material and overconsolidated, andthe non-cohesive soil arefirm to stiff.Gravel content includes local into loose and dense. Carboniferousrock types as well as exotic ones, andin some areas acorrelation exists between Engineering Problems associated with Superficial gravel andunderlying bedrock. Such local (Unconsolidated) deposits correlationsare not mappable, and with the exception of theCarboniferous mudstone gravel, I. Backfill and Made Ground - Engineering were foundtohave nosignificant effect on Problems geotechnical properties.In the case of the tills In general, these deposits areunsuitable in their withmudstone gravel content, higher plasticities presentstate for the support of light-weight, (CH)have been measured andthe till becomes single-storey structures(safe bearing pressure darker grey in colour. Geotechnical properties are veryvariable (Tables 21 and 22), withthree - 50 kPa). Miningwaste has beenobserved to producecontamination of groundwater giving factors, lithology, depthand weathering state highsulphate contents and a subsequent risk of being the main causes of these variations. damage to concretefoundations. This risk should be appreciated in the vicinity of suchwaste tips, Groupings of Superficial Deposits in Engineering regardless of local geology. Terms The soils ofthe study area fall into sevenmain 2. Peat - Engineering Problems groupingsengineeringin terms, indicated as If peat is identified as being present at a site, care previously. The relationship of these groupings to will have to betaken to determine its thickness the geological interpretations of the soils are: andextent (which is notlikely to begreat) to EngineeringGrouping Geological Interpretation avoid structures being foundedon it, as it is highly compressible. 1. Backfill andmade Backfill and made ground ground ground 3. Alluvium Engineering Problems 2. Peat Peat - 3. Normally consolidated i) Lacustrinealluvium Generally low maximum nettbearing pressures cohesive soils ii) Alluvial clays makealluvium problematic even for the support and silts of light-weight, single-storey structures, though iii) Estuarine alluvial gravelly layers showmuch higher bearing clays and silts pressures (100 kPa forfoundations 1.2 m wide, 4. Loose sands and i) Wind-blownsands reducing to 80 kPa forfoundations greater than gravels ii) Estuarine alluvial 3 m wide). Theheterogeneity of the deposit sands makes foundation problemsmuchmore iii) Stratified glacial site-specificthan in the case of theestuarine Table 2 1 Sunmlary geotechnical data for Till (Boulder Clay)

I I Moisture Liquid Plastic 'lasticity Bulk Dry Speci f i c Content Limi. t Limit Lndex Dens' ty Cravi ty Density Clay % % % % Mg/m Mg/m % Si% It 997 286 284 284 549 51 11 106 106 Till (Boulder Clay) sandy, silty clay ui th gravel . 31(8.0) 16(3.75) 13t4.3) 2.18(0.15) 2.25(0.25) 2.62(0.07) lO(8.4) 14(12.8) 37(21.938(24.7)

S;dlo61 Gryelo6 I 1-180 2-50 3-67 7-33 2-39 1.60-2.50 1.49-2.30 2.45-2.68 042 0-68 0-91 0-100

FILE FORMAT

No. of Jndrai ned Angle nf Opti mum samp 1 es zohesion Internal dois ture so3+ CBR FrI cti on Dry Den i tyConcent Comments 1 Average(Standard kPa ("1 n /MN m /yr m/s Mg/m "I Deviati on)* I 603 603 29 84 81 46 Variable deposit, stiff tohardj Range when fresh-Weathering proved to; 291 2.5~1, stronger vith depth. +t quotedwhere no. 112(73.1) 2(5.9) 3,2,4 3.2.4 2l 1.96(0.13) 11.3(3.4) 7.6 1 1.2 Water ingress and-perched vater! of samples 2 10 (0.5) in granular soils.Suitableas + class values fill at naturalmc.Embankment see relevant I I slopes 1:2.Cutting slopes 1:2- tablesbelow 0-619 0-34 I 3~1O~--lxlO-~I 1.61-2.21 I 6-21 -2-8.4 -0-3.2 2.5 vith drainage. CBR 5%.

1 I I i r SO insoil Descrionpti of Mv . Plasticity Index Total 2:3 water In Compressibi.lity m'/MN Examples 2cv / 1 Class m /year fiange Soil Type Class SO3 extract Groundwater CLAYS 5 Very high above 1.5 Very organi c alluvial 1 LO. 1 Greater I claysand peats Montmorillonite 30 parts than 1 i<0.2% I in 100 000 I 0.3 - 1.5 Normallyconsolidated High plasticity alluvia1 clays, eg. 2' 0.1 - 1 25 2 '0.2-0.5% 30 - 120 estuarj ne clays partsin 1 lHigh I I 100 000 3 1 - 10 I25 - 5 3 Medium 0.1 - 0.3 Fluvio-glacialclays Medium plastjci ty I Late clays 3 10.5-1.0% 1.9 - 3.1 120-150 1 ! grams/ partsin 2 Low 0.05- 0.1 BoulderClays 4 10 - 1-30 1 15 or less Low plasticity I litre 100 000 -- SILTS 4 1.0-2.0% 3.1 - 5.6 250-500 1 Verylow , below 0.05 Heavilyoverconsolid- grams/ partsin atedBoulder Clays. I 15 litre 100 000 Stiff weathered rocks *' 'loo 1 i 5 >2.0% 5.6 After iicad Q982 ) 500 parts After Lambe and Whitman (1979) grams/ jn 100 000 1 j tre COEFFICIENT OF VOLUME COMPRESSIBILITYMv COEFFICIENT OF CONSOLIDATION Cv Aftec.BuildingResearch Establishment (1975).

SULPHATES IN SOILS AND GROUNDWATERS 66 Deeside(North Wales) Thematic Geological Mapping

Y I s d

0 In rl u I

r) J: (0 a Qi I 0, 9 4 rl

n tn I$ a

P 0

m ? m rl d d Y Q,

a, 2 c m > I 2

r 1

3 rl 2 > Deeside (North Wales) Thematic Geological Mapping 67 alluvium. No groundwater problems interms of by the use of geotextiles. high sulphate contents were identified. 4b. Estuarine Alluvial Sand - Engineering Problems 4. EstuarineAlluvium - EngineeringProblems Thismaterial has highersafe bearing pressures Inherent in their low-lying, tidal to supratidal (107-220 kPa) thanthealluvial clay, which location, theestuarine alluvium has characteristic increasewith depth, making the depth of groundwater problems associated withit.The foundationscritical to theirstability. Loose sand water-table is ubiquitouslynear-surface (1-3 m is marginally suitable for supportthe of depth) and may reach the surface in wet weather. light-weight,single-storey structures atsurface Thesediments aregenerally saturated with level. However, thesituation improves with moisturecontents commonly approachingliquid depth, as thesand becomes mediumdense at limits forthe cohesive soils, and therisk of about 10 m depth. Its loose nature, particularly at runningconditions being produced.in the shallow depths, may cause blowing during non-cohesive soils. Excavations require StandardPenetration Tests, renderingthe results groundwatercontrol in the form of well-point unreliable,and may necessitate deeper than usual dewatering and/or sheet piling withpumping to sheetpiling to prevent boiling. Water ingress at preventflooding, piping andrunning conditions. coarser, cleaner horizons is also common. Ingeneral, such work should be avoided at peak California Bearing Ratios of 10% have been tides. Tidally-inducedfluctuations in hydrostatic assumed for preliminary design purposes. pressures make S.P.T. values, and the subsequentlycalculated safe bearing pressures, 5. LacustrineAlluvium EngineeringProblems unreliable, unless sucheffects are accounted for. - The loose nature of thematerial necessitates Problems of stabilityand settlement have been shoring of vertical excavations to ensure stability. observed, mainly inthe softer clays, and "as a Calculated safebearing pressures are low, but consequence of thevariable composition and increase to reasonable values withdepth, making fabric of glacial clays, thepresence of weaker, piling of foundations to these denser materials the more compressible layers understronger, stiffer most reliabletechnique. Safe bearing pressures layers should be expectedrather than considered for varioussites estuarineon alluvium are as an exception"(Marsland, 1977). S.P.T. results summarised in Table 23. No seriousgroundwater should be treated with scepticism. sulphate problems are apparent as long as a good qualitydense cement is used below the 6. Heterogeneous deposits (Head) - Engineering water-table,since seawater chloride counteracts Problems theeffects of the sulphate.Higher groundwater Where the head is coarsergrained, and overlies sulphateconcentrations, however, have been finer graineddeposits, perched water-tables may observed in the vicinity of mine waste tips. be found withinit. These may lead to possible 4a. Estuarine Alluvial Clay - Engineering runningconditions excavationsin which will Problems require pumping. Very low safebearing pressures (23-50 kPa)and Head is formed by slow, down-slope movement high compressibilitycombine to make thisa difficult material for thesupport of even and accumulation, and there is always a possibility thatit may containshear planes. Increases in light-weight,single-storey structures; generally, pore pressure, undercutting of slopes or loading at piling is essential. Largesettlements can occur the top of slopes may reactivate movement, with small loads, and differential settlementscan causing failure. If head is identified,therefore, also occur.Better materials arefound at depth, though skin-friction values inthe softclay can careshould be taken to examine samples €orthe presence of shear planes. Sloping sites(including vary from zero to 7 kPa for bored piles or 8 kPa fordriven piles, makingthis foundation type, those wherethe gradient is onlya few degrees) should also be inspected for the presence of small where adopted, complex to assess. curved ridges representing the toes of solifluction Excavated facessoften rapidly on exposure to lobes. rain, so should be protected as soon as possible. Piles founded on strongerunderlying strata may Bogging down of plant in the clay, particularly in wet weather, is avoidable by placing a layer of be necessary where the head is weak and sheared. No appropriatebearing pressure dataare gravel over the site prior to work commencing or available. There is no evidence of high sulphate 68 Deeside (North Wales) ThematicGeological Mapping

Table 23 Foundation loading criteria for Esturine Alluvium at different individual sites within the Deeside area ...... -

Safe Bearing Pressures onpiled Piled

Alluvial,Clay 25-50 kPa 7 kPa (bored) 6 kPa (driven)

Alluvial Silty Clay 23 kPa 0 kPa ( loose) 0 kPa ( loose)

Sandy Silt 50-70 kPa

Assorted Alluvium 20-57 kPa

Rafts on Compacted, 4 Crushed Rock 95-1 00 kPa

Alluvial Sand 100-1 60 kPa greaterthan 3.h depth 300 kPa 335-850 kPa (allowable)

Clay Lens 115 kPa Deeside (North Wales) Thematic Geological Mapping 69 contentsassociated with head, all butone of the resultsunreliable, and give rise to perchedwater fewsamples tested falling into class 1 (Building within the sand and gravel deposit. ResearchEstablishment 1975). (However,note Differentialsettlements are a problem caused by thecomment inthe Fill and Made Ground theheterogeneity of thedeposit and, combined section, above, with regard to sulphate contents in with the effect of hydrostatic pressures on S.P.T. the vicinity of mine tips). results, make safebearing pressures very site-specific,generalisationand difficult. 7. Glacial Sand andGravel - Engineering Nevertheless,groupingsoilthis can be Problems characterised,tosome degree inthis respect Maximumsafe bearing pressures of the stratified (Table 24). sands and gravels are variable and largely depend Forcuttings, side slopes of 1V:2H havebeen ongravel content; where no gravellayers are recommended forthe glacialgravels, grading to present,safe bearing pressures of 80 kPa (strip 1V:3H forthe more sandydeposits. Counterfort footing 1 metrewide) have been quoted, while and toe drains maybe necessarywhere the withthe presence of gravel,values of 130 kPa water-table is high. Well-graded glacialgravels have been used (Table 20). Forsand and gravel can be used as embankmentfill with side slopes withclayey orsilty layers, nett safe bearing of 1V2H. C.B.R:’s of10% may be used for pressures are generally between 100 and 200 kPa, preliminary pavement design purposes. but where the clay occurs as a matrix, lower safe 107 bearingpressures of 53 to kPa can be 8. Till (Boulder Clay) Engineering Problems expected.The clay layers themselves vary from - very weak to very stiff, with the latter giving safe Geotechnicalproperties are very variable within nett bearing pressures of 500 to 600 kPa for pad theglacial till (Tables 21 and 22), withthree foundations,with an end bearing pressure of factors, namely lithology, depthand weathering about 900 kPa for piles.Water ingressis a statebeing the main causes of thesevariations. ,problemat the coarser horizons,and intercalated These three factors combine in a complex manner clays and sand and gravel can give rise to perched andmake generalisations and predictions about water-tables.The heterogeneity of thedeposit engineeringbehaviour in this material difficult. can giverise to variationsgeotechnicalin Nevertheless,several engineering problems have propertieson sitea scale, making differential been observed to be associated with one, or more, settlementsa possible problem. As a fillmaterial of these factors. the glacial sands are suitable only where no clay is Maximumnett safe bearing pressures range from present. 80 to 500 kPa. Theupper weathered zone and Being well-sorted and of low cohesion, the glacial softer claysoccupy the lower part of this range sandsand gravels are characteristically prone to from 80 to 240 kPa, withan improvement in running,causingdeteriorationrapid of weatheringgrade or an increase in depth of the excavations.Shoring is, therefore,necessity,a claylayer giving higher values. Piles in the and where long-term stability is required, cutting weathered zone can be expected to haveskin slopes back to 1:l andperhaps covering with a friction values of16 to 19 kPa (bored), 24 to protectivematerial (for example, coarse-grained 29 kPa (driven), and safe end bearing pressures of sandand gravel, or vegetation) maybe needed. 240 to 270 kPa comparedwith 40 kPa skin Groundwatercontrol during excavation can fraction (driven or bored) and 630 to 950 kPa safe reducethese problems, especially coarserin endbearing pressures in the fresh, underlying materialwhere high water inflows can occur, material.The upper part of thesafe bearing thoughsupport by timberingor sheet-piling will pressurerange is occupied by verystiff to hard, be required during pumping. unweatheredclays, and unweathered to slightly weatheredstony clays. These areend-member Highhydrostatic pressures pressures can occur in conditions,and various combinations of depth, granularmaterials, exacerbating abovethe weathering and lithology give rise to intermediate problems. Where thesand and gravel is overlain properties.Safe bearing pressures for various by a clayey layer, heaving and sagging conditions sitesare summarised inTable 25. S.P.T. and canarise excavation,on andthere is an triaxial test resultsrespond similarly to these ever-presentdanger of suchconditions existing variables,and piping in sands can render the just below thedepth of investigations.These formerunreliable. Softer horizons may not hydrostatic pressures, where present, render S.P.T. supportpiles or may make themuneconomical, 70 Deeside (North Wales) Thematic Geological Mapping

Table 24 Foundation loading criteria for Glacial Sand and Gravel at different individual sites within the Deeside area . . ._ - . - . .. . .

End Pressure Skin Riction

Sandand Gravel with clayey zones 200 kPa (BZ!.Om) 200 x B kPa (B

Very stiff clay zones 500 kPa (strip) 600 kPa (pad) 900kPa

Sandand Gravel wi"& thin clay band 133 kPa

Sad andGravel wi+& claylayers 200-300 kPa (0.51~wide strip footings 1

Sand andGravel clay zones andlenses of clay

Sand andGravel firm claybinding 53-107 kPa

Sand and Gravel with claybinding 100 kPa 630 kPa Deeside (North Wales) Thematic Geological Mapping 71

Table 25 Foundation loading criteria for Till (Boulder Clay) at different individual sites ' within the Deeside area .-

SUB UE3flING PRESSURES

marld Pressure Skin Friction

Unweathered,gravelin kPa 230 a (fitrip) 630 kFa at 7.0 rn depth matrix of clayey,very sandy 2Y0 kPa (square) silt, withcobbles & boulders

Firmsandy clay with stone 100 - 150 kPa at 1 In inclu13ions,slightly weathered depth

Stiff sandyclay with stone 150 kPa (strip) inclusionsand lensee of sand180kPa (pad) andsand and gravel

Firm to hardsandy clay with 145 kPa (Rtrip) 265 kPa 19 kFa (bored stoneinclusions sandand170 kPa (pad) 29 kPa (driven) lensee.Slightly weathered Unwea theted 950 kPa 40 kPa (bored/driven 1

~ ~ ~ ~~ ~ ~ Firmto stiff eandyclay withstone inclusions and lenses of sand. 260 kPa 18kPa (bored) Unweathered,very stiff to 40 kPa (bored/driven) hard Slightly weathered 27 kPa.(driven) Moderatelyweathered 240 kPa 16kPa (bored) 24 kPa (driven)

Firm, brown, stonyclay 133 kPa

Firm to stiff sandy clay 160 - 165kPn (strip) withstone inclueions and 160 - 245 kPa (pad) occasional silt pockets

Stiff,aandy silty clay with 268 kPa (strip) a little c, rn c f gravel

Clay 125 kPa (strip) 145 kPa (pad) )same site )dif Eerent 300kPa (strip))clay 350kPa (pad

~~ ~ ~ Sandyclay,laminated with 250 kPa stonesand sand and gravel S an dy clay Sandy 250 kPa C lay s in stonygroundClays in 160 - 520 kPa

Sandy clay with stones Allowable Below weathered zone 220 - 290 kPa (F.S. * 3) Inweathered zone 180 - 230 kPn

-~-- ~ Stiff(top) to very stiff at 150 - 200kPa depth,withlayersthin of (Allowable) water-bearingsand

Sandy, siltyclay with a little gravel.Weathered 00 - kPa110 (Allowable) U n w eathe red 100Unweathered - 150 kPa

~~~~ ~ ~ ~ stiff upperglacial clay 2UO kPa (strip) 240 kPa (pad) Firm, wea thetedmaterial RO kPa Glacialsand (loose-medium 150 - 200 kPa (R>1 m) dense 1 150 - 200 x 13 kPa (13~1In) (less if underlain by clay)

Lower glacialclay (stiff1 110 - 140 kPa (strip) 130 - 170 kPa (pad)

Lower glacialclay (very 230 - 420 kPa (strip) stiff to hard) 500 kPa (pad 1 72 Deeside (North Wales) Thematic Geological Mapping and granular materials are subject to seepage and collapse duringboring, making driven piles preferable in such lithologies. In addition, sloping siteshave been observed to reduce expected safe bearing pressures, and differential settlements can resultfrom localised variations in geotechnical properties.Underlying lithologies can produce unexpected local variations, notably a decrease in safebearing pressures in sands where they are underlain by clay. Groundwater can present problems in the form of perchedwater-tables andseepages morein permeablegranular materials. Clays areliable to softeningon exposure to rain, so excavations should be protected as soon as possible. No groundwatersulphate problems were observed, withthe exception of onelocality where a high sulphatecontent and a pH of3.2 occurred.This may havebeen due to contaminationfrom a nearbymine waste-tip. Excavations may require well-pointdewatering areas in of high water-table,and will require support to ensure stability. Atnatural moisture content the till is ingeneral suitable as afill material. Side slopes of 1V:2H have been recommended. Cuttings in the material should be stableat slopes of 1V2H to lV:2.5H, though shallower angles and provision of drainage to avoid pore-pressure build-up may be required, especially inthe granular deposits, and most particularlythe sands. C.B.R. values of 5% may be adoptedfor preliminary pavementdesign in these materials. Deeside (North Wales) Thematic Geological Mapping 73

SUMMARY OF GEOLOGY relatively constant between WNW to ESE, and NW to SE. The cleavage is generallyconsidered to The generalised geological sequence of the area is have formedregionalduring atectonic shown inFigure 10, and a simplified geological compressionalevent which occurredbetween the sketch map is given in Figure 4. end of theSilurian and the middle of the The followingThe geological summary is a Devonian. comparativelybriefreview of mainthe observationaland interpretive findings of the Carboniferous fieldsurvey undertaken between 1985 and 1987. Strata of Carboniferous age can be assumed to rest It is intendedto be used as aidtoan unconformablySiluriantheon rocks. The understanding the 1: 10 OOO/ 10 560 geological base unconformablecontact is notexposed, but it can maps and open file reports listedin Appendix A. be mappedwith precision as it has markeda Furthermore,it lists, incontext, most of the topographicexpression. Rocks of Devonian age scientific literature relevant to the area. are presumed absent, as is the case in surrounding Thebedrock geology, outcrop,in comprices areas. unconformityThe is angular an sedimentary rocks which range in age from Upper relationship, and the Carboniferous rocks, dipping Silurian(Lower Ludlow) toTriassic, spanning gentlythetoeast and northeast, overlie a approximately 200 millionyears. Anoverburden previously folded and eroded Silurian terrain. of consolidatedglacial and post-glacialsediments (Quaternary to Recent) blankets much of the area. Carboniferous Limestone (Dinantian) Thebedrock sequence can be regarded in general Thefirst major study of theCarboniferous termsas a gently eastward dipping sequence, but Limestone of north Wales was carriedout by indetail is considerablymore complex due to Morton (1870) whorecognised a general regional faulting and local folding. tripartitestratigraphy of LowerBrown, Middle White andUpper Grey limestones.He applied Silurian thisstratigraphy to the Mold districtin 1878. Subsequentworkers in this area have tended to Elwy Group substantiateMorton'sclassification (e.g. The oldestrocks of thearea are Ludlow (Upper Neaverson, 1929, 1946). recently,More Silurian)strata (c.350 mthick) assigned tothe Oldershaw (1969) has recognised four lithological Elwy Group,and are exposedin theClwydian unitsabout Halkyn Mountain, andBanerjee Hills along it: westernmargin. Although this (1969) has establishedsimilar a stratigraphy terrain is well-featured,with relatively little further south, near Rhydymwyn. superficial overburden, the bedrock is surprisingly The limestones(carbonate sediments) in this poorlyexposed andconsequently there are no report have been described using the classification extensivesections. These rocks were included in of Dunham (1962). involvesThis the the area mapped and described by Simpson (1940). interpretation of texturalfeatures and is ideally They comprise mostly grey, thinly laminated, silty suited to rapid assessmentbased fieldon mudstones withsubordinate sandstones and observations. Furthermore,produces it data localised slumpedhorizons anddebris flows whichcan be represented as graphic logs (Figure ('Disturbed Beds'). The sandstones have been 9) demonstrating grain-size variations in a section. interpreted regionally(Warren andothers, 1984) as thedistal products of turbiditycurrents TheDunham classification fourhasmain depositedin a marine environment between 420 categories: (1) grainstone,(2)packstone, (3) and 410 million years ago, and the disturbed beds wackestone and (4) calcitemudstone. These are as slumpand slide units which developedon the definedin the glossary withother less frequently seafloor. No fossilswere foundduring the used descriptivecategories. In general terms, the surveybut Woods andCrosfield (1924) recorded averagegrain size of the limestonesdecreases graptolites from some localities in the area. fromgrainstone through categories 2, 3 and 4. Theindividual carbonate grains are typically Dipand strike of theserocks varies considerably greaterthan 0.1 mm insize. Classification of the (maximum dip 60°), reflecting their folded nature. limestones in this way provides direct information The rocks are also tectonicallycleaved, and relevanttheresourceto characteristics and particularly so inthe finer-grained lithologies. engineeringproperties. Two types of carbonate The cleavage is steep (65' - 90") and its strike is grainare recognised, skeletal and pelloidal. The

Deeside (North Wales) Thematic Geological Mapping 75 formerare fragments of marine fossils andthe reflectsaprolonged period of stablecarbonate latterwere formed by sedimentary processes on platformdeposition inshallow-marine,a high the sea-floor. energyenvironment in warm subtropical seas. A local conglomerateoccurs towards the top of the TheCarboniferous Limestone outcrop forms a formation.Microfossils (e.g. foraminifera) of well-featured escarpment which trends NNW-SSE Arundian age havebeen obtained from the along the western side of the study area. Natural formationin addition to ascattered fauna of exposure is good in the south of this tract, which fossil brachiopodsand corals (Somerville and widensnorthwards from 2.5 to 4 km, andin the Strank, 1984b; and see Palaeontological Reports in areaabout Halkyn Mountain. Complete exposure Appendix A). of substantial parts of the stratigraphy is available in the quarries of the district. The sequence dips Leete Limestone gently to the east in the south of the area and has TheLeete Limestone (c.75 m thick)includes a a morenortheasterly dip in the north. The dip complexarray of carbonatesediments. It typicallyvaries between 5’ and 15’ butin the comprises irregularly bedded, dark brownish grey, vicinity of theNant Figillt Fault (see Structure porcellanouswackestones and calcite mudstones, below) open periclinal folding occurs. with fine- to coarse-grained skeletal and pelloidal packstones. A thickunit of pale grey to white Thefollowing sections give brief descriptive and pelloidalgrainstones and packstone-grainstones interpretive details of the constituent formations: occursin the lower part of theformation. The Foel Formation formation as a whole was probably deposited in a The ‘Basement beds’of theCarboniferous fluctuating environment of peritidal and platform Limestone are poorly exposed and were only seen carbonatedeposition withshort periods of in small isolatedexposures, e.g. south of emergenceand desiccation. The formation has (SJ 1700 6783),where variably yieldedmicrofossils of Holkerian age (Somerville calcareousanddolomitised, locally oncolitic, and Strank, 1984a and b; and see Palaeontological packstones and grainstones overlie poorly exposed Reports in Appendix A) and is typified by a large redclays (Strahan, 1890; Davies andothers, in brachiopod named Daviesiellallangollensis. The press). Thesehave yielded microfossils of late upperpart of theformation maybe Asbian in Chadian age (seePalaeontological Reports in age. Appendix A) implyingthattherocks are Loggerheads Limestone approximately 350 millionyears old. The main Thisformation (c.170 thick)m bears some body of theFoel Formation is a limestone similarities to theLlanarmon Limestone but is sequence comprising approximately 20 m of dark somewhat finer-grained in character. It comprises brown,pelloidal grainstones withscattered pale grey,cream and white, massive to rubbly oncolites,porcellanous pelloidal wackestones and bedded,pseudobrecciated, pelloidal and skeletal dolomitised,fine-grained pelloidal packstones packstones and subordinate packstone-grainstones. withcarbonaceous laminae and scattered plant Thinlight grey clays (< 30cm thick)occur, remains.These sediments record theinitial commonlytowards the top of theformation. The transgression(inundation) of theCarboniferous upper parts of the formation are well exposed in seas overthe Silurian landmass, with alternating all of the large working limestone quarries of the phases of peritidaldeposition and quiescent areaand detailed sections have been measured. deposition. Generalised sections of these quarries are given in Llanarmon Limestone Figure 1 la,with suggestedcorrelations. Most of The base of thisformation is marked in the theformation is Asbian in age (Somervilleand southwest by Llwyn-y-franthe Sandstone Strank, 1984a and b; andsee Palaeontological (member),a yellowish brown, fine- to Reports, Appendix A). medium-grained,dolomitised,calcareous Correlations of thelimestones across the area are sandstone, up to 20 mthick. The sandstone based onthe cyclic repetition (‘minor cyclicity’) marks a second, more importantregional marine of variationslithology. in This cyclicity transgression which drowned an extensive area of (Somerville, 1979) is veryapparent in the upper north Wales (Somervilleand Strank, 1984b). This 50 m of theformation and mostis readily is succeeded by c.150 m of white to pale grey and observed in Cefn Mawr and Trimm Rock quarries cream, well sortedpelloidal skeletaland [SJ 202 635 and SJ 191 669 respectively]. Within grainstonespackstones.and limited The eachcycle there is anupward increase in grain lithologicalvariation both vertically and laterally CEFNTRIMM MAWR ROCK HENDRE PANT PANT-Y-PWLL-DWR

i"W 5 iI I LLM WPG

SECTION BASED ON , L BOREHOLE *5 M WPG CORE 5M

PWLL-DWR -

- HENDRE-pAy:j %

BOREHOLE m5 CONTINUES 'R

Figure lla Detailed correlation of the Limestone sequences of the main working quarries (Graphic logs compiled by S D G Campbell and J R Davies). Cefn Mawr Limestone correlation Figure llb Detailedcorrelation of theLimestone sequences of the PANT main working quarries (Graphic logs compiled by S D G Campbell (SJ 1 gg 702) Calclte Mudstone, and J R Davies). Loggerheads ,Limestone correlation. with an inset Shale or bentonite of the position of the quarry sites Wackestone Wackestone-Packstone Packstone

. Packstone-Grainstone

Grainstone 3rc Rudstone 3 MWPG Horizontal lines are prominent CEFN MAWR * bedding planes (SJ 200 634) The horizontal width of the boxes reflects average grain size -4- Vertical scale 0 P I

5 * I1 Om + Karsticsurface (Palaeokarst) U PalaeosolP (fossil soil) usually bentonitic U I 3rc X Fossil roots/rootlets A I \ I 0 * U 3rc Crinoidfragments \ I \ ;i; 0 I A U u Brachiopodshells I U 'MAIN 0 I H 5 Mottling SHALE I A U 0 o Chertnodules U 0 Colorual corals % p Solitarycorals

Stylolitic surface \' U \\ A \\ L \ \\ UI I \ ', *

U

-E PANT-Y-PWLL-DWR (SJ 1 90 720)

0 TRIMM ROCK (SJ 191 660) U 3rc A 3 3rc

P 3- *U 3 5 5 5.

uMWPG 78 Deeside(North Wales) Thematic Geological Mapping

size withpackstones passing upinto grainstones. are recognised and can be mapped across country. In lower parts of theformation, the next cycle The lower is the ‘Thick shale’ and the upper, the succeeds with or without an initial coarse-grained ‘Main shale’. A coral-richhorizon with abundant bioclastic deposit, andthen a sharp reversion to colonial and solitary corals occursapproximately finer grained lithologies. In places, stylolites and 10 mabove the ‘Main shale’. Theupper parts of small carbonate nodules are developedbetween theformation are very mudstone-rich (c.50°/o). cycles. Darkgrey-brown mottling (patches of White and black chert nodules, up to 10 cm in 0.5-2 cm) is also common inthe lower parts of size, oftenoccur along selectedbedding planes, many of the cycles. Towards thetop of the mainly at high levels inthe formation. The formation,the cycle boundaries are made more formation has richa fossil content and large obvious by theappearance of light-grey clays productidbrachipods are very common, while a which reston an irregularbedding plane surface stratigraphicallyuseful band with GirvanelZa withinwhich are preservedfossil plant roots and occurs low inthe formation. In the middle and rootlets. The tops of these cycles are commonly upper parts of the formation, there is evidence of richin coarse fossildebris. Laminar carbonate tectonism andinstability during deposition with (calcrete) is sometimesobserved and iron oxide low-angle slidesurfaces (e.g. at Waen Brodlas staining is common. The clays themselves have Quarry, SJ 1875 731 5; see front cover) and rotated been interpreted as being potassic bentonites fault blocks (e.g. PantQuarry, SJ 200 702) (altered volcanic ash)and represent a fossil soil evident.In the vicinity of HalkynMountain, the (palaeosol) preserved on anirregular karstic formation is thicknessreduced in to (palaeokarstic)surface with depressions up to approximately 50where m it is overlain 50 cm deep.Each cycle is interpreted as a unconformably by cherts. gradual shallowing of generalthe marine carbonateplatform environment, with eventual Minera Formation emergence of a low topography land surface. The In thesouthern half of thearea (south of the surface was subsequentlydrowned and followed NantFigillt Fault; see below) theMinera by another phase of gradual shallowing of the sea. Formation (c.170 m thick) is present. It thins progressively to the north.Much of the George (1974) ‘and Ramsbottsm (1973, 1977) formation is verysimilar to theCefn Mawr suggest interpretations for the cyclicity. Limestone, butdiffersit inthe presence of Cefn Mawr Limestone massive and cross-bedded, fine- to This formation (c.120 m thick) mostly consists of medium-grainedand occasionally pebbly, thinlybedded,brown dark-brown,and calcareous andquartzitic sandstones up to 40 m fine-grained pelloidal, skeletal packstones, thick. The basesof the sandstonesare sharp. wackestones andshaly mudstones. Interbedded, Scattered fossils, trace fossils and carbonaceous mainly towards the base, are thicker-bedded, pale, materialoccur in the sandstones. Pebbles inthe coarser packstone-grainstones.The basal part is sandstones aregenerally of veinquartz. The exposed in all of the largeworking limestone sandstones, whichrepresent animportant change quarries(Figure 1 lb). Althoughthe Cefn Mawr sedimentin provenance, are either marine Limestone is substantially finer grainedoverall transgressive sheet-sands or progradingfan-delta thantheLoggerheads Limestone, similar a systems. With the disappearance of the sandstones cyclicity is present.Generally the karstic surfaces to thenorth, theMinera Formation passes and bentonitesand are absentbut some are laterallyinto the Cefn Mawr Limestonein part. occasionally observed (e.g. HendreQuarry), A particularlycoarse-grained crinoidal limestone suggesting thatemergence fromthe general low commonly occurs at the top of the formation. energymarine carbonate seas wasless common. The base of theformation is marked by an Millstone Grit Series (Namurian) . obvious colourchange in the rocks, with the brown anddark brown limestones of the Cefn Halkyn Formation Mawr Limestone contrasting with the pale grey of Theformation comprises ‘Cefn-y-Fedwthe theunderlying Loggerheads Limestone. This Sandstone’ of earlierterminology (Strahan, 1890) boundarycoincides with the Asbian/Brigantian at the base, the Holywell Shales, and the Gwespyr stage boundary (Somerville and Strank, 1984a and Sandstone atthe top. A chertunit occurs at the b) andthe Cefn Mawr Limestone is entirely base inthe north. Theformation crops out in within the Brigantian stage. two main areas, along theeastern margin of the limestone terrainandsouth of Hawarden Two thick mudstone (shale) packets (3-4 m thick) [SJ 3 16 6591. There is markeda lateral and Deeside (North Wales) Thematic Geological Mapping 79 verticalvariation inthe constituent lithologies. occurs at the base of the formation and below the Thus, the ‘Cefn-y-Fedw Sandstone’ thinsout ‘Cefn-y-Fedw Sandstone’ south of Halkyn. North towards the north and is absent in the vicinity of of Halkynchertsthe restwith apparent Holywell; it is replaced laterally by a locally thick unconformity on akarstic surface of theCefn chertunit at the baseof theformation, and by Mawr Limestone which is thus greatly reduced in mudstones. TheGwespyr Sandstone has a thickness. Thecherts (known locally as the complex distribution,and was probablyderived PentreCherts around Holywell) thinlyare fromthe north.Significantly, it is afeldspathic laminated, black andwhite, glassy chertsand sandstone, instark contrast to thequartzitic flaggy, cherty siltstones. Theyare structurally ‘Cefn-y-Fedw Sandstone’ underlyingand complex; disharmonic tight folding and low-angle sandstones of the MineraFormation. As such, it faulting have been observed at many localities. is similar to the typicalfeldspathic sandstones of This structure is interpreted as being in part due the Coal Measures. With theexception of the to collapse of thecherts into solutioncavities sandstones and cherts,the formation is poorly withinthe underlying limestones and also to exposed, withexposure of the finer grained gravitational collapse on a slope. Thenature of lithologies being restricted largely to sectionsin thefolding and low-angle faulting suggests that streams. Thesandstones and cherts have been thecherts were notfully lithified at the time of quarried and exposed at many sites and they form theirdisruption, implying that the solution and strongly featuredground which also provides collapse occurred largely during the Carboniferous limited exposure. period or soon after.Their age is problematic. Ramsbottom (1974) considered they are Dinantian ‘Ce Fedw Sandstone’ The sandstones (up to fn-y- in age butthey are thought here tobe more 80 m thick) at the baseof the Halkyn Formation probably Namurian. are well exposed Gwyn-bryn in Quarry [SJ 214 6231, south of Gwernymyndd,where the The mode of theirformation is problematic.The crudelycyclic nature of sedimentsthe is main point at issue is whether the chert formed as displayed. Thefirst element of the cycle is a a silica gel onthe sea floor or originated by poorly sorted, relatively mature, pebbly sandstone, replacement of existingstrata. The evidencehere occurring in units ofc.2 m. The larger clasts are suggests thatreplacement is animportant factor well-rounded,relatively low sphericity,quartz andthat much of the process of silicification grains. These pass upwardsinto finer grained occurred soon after deposition of the strata while quartziticsandstones with well-rounded and high they were still plastic habit. in Local sphericitygrains (mature). Bedding is flaggy to interbedding of chertand calcareous siltstone massive, with low-angle cross-bedding evident. suggests thatthe chertified strata were likely to Continuingupwards in the cycle, flaggy bedding have been calcareous siltstonesprior to their is on thecentimetre scale and the lithology is an silicification. A sparsemarine faunaand the intercalation of cherty(silicified) fine-grained occurrence of fossil crustaceansinthe cherts sandstones, siltstones and mudstones. These beds suggests thatthe strata were depositedin a low werevariably calcareous prior to silicification. salinity, low energy, possibly lagoonal Theirhabit is notdissimilar to theflaggy environment. Occasional incursions of coarser limestone andmudstone intercalations of the sand,probably derived fromthe south, record MineraFormation, the only real difference being short-lived,higherenergy conditions of theextent of silicification.The flaggy chertsare sedimentation.The spatial association of the thensucceeded by another massive sandstone. As thickestdevelopment of thecherts with the the sandstonesthe tracedare northwards, the pronouncedunconformity at their basemay not medium- to fine-grainedelement of the cycles be fortuitous. becomes increasinglydominant, and intercalations Halkyn Formation general The main body of the of siltstone and mudstonewith less chertification - formation comprises 250 to 350 m of dark grey increase in thickness at the expense of the and brown,well-beddedand and laminated sandstones. The sandstones dieout just to the mudstones, silty mudstones and black fissile north of Halkyn 21711. In thearea south of [SJ mudstones. These thinlybedded sediments are Hawarden,the lower part of the formation intercalated with thin yellowish brownand white comprises quartzitic sandstones. quartzose sandstoneswhich vary from fewa Chert Inaddition to chertsintercalated with the centimetres to severalmetres thick. Thin coal ‘Cefn-y-Fedw Sandstone’ south,the ain horizons with seatearths occur at various localities substantialsequence (maximum 180 m) of cherts butare not laterally extensive. The environments 80 Deeside(North Wales) ThematicGeological Mapping of depositionwere fluvio-deltaic with periodic approach is retained here to facilitate comparisons marineincursions. The thin sandstoneunits with other areas. decrease in thicknessand abundance towards the The most recentaccounts of the‘Flintshire north, where the sediments have been termed the Coalfield’ of whichthis areaforms anorthern Holywell Shales. part,are those of Magraw and Calver (1960) and Thesequence of the Holywell Shales was proved Calver and Smith (1974). The earlieraccount of in its entirety by the Abbey Mills boreholes sunk Wedd andKing (1924) providesimportant detail. near Holywell (see Appendix C). Occasional Coal Measures occupymuch of the central, ‘Marine’ bandsyield the characteristic and northernand northeastern parts of the area. stratigraphicallyuseful goniatite zonal fossils of Exposure is verypoor, mainly due to the theNamurian and these havebeen described considerablecover of superficialdeposits, and extensively forthe area (Hind and Stobbs, 1906; most informationderives from boreholes, Sargent, 1927; Wood, 1936; Jones and Lloyd, 1942; mine-shafts andunderground workings. The Ramsbottom, 1974; and see Palaeontological sequencevaries in thickness from 360 m to Reports,Appendix A). The zonal fossil 410 m. Cravenoceras Zeion has not been found at the base Productive Coal Measures of the Holywell Shales inthe north of thearea .In terms of earlierclassifications, the Productive whichotherwise includes fairly acomplete Coal Measures arethe‘Grey Measures’ (cf. succession of goniatite zones. ThePendleian Calver and Smith, 1974) andare succeeded by strata below the horizon of Cravenoceras ‘Red Measures’ which lack anysignificant coal rnalharnense are condenseda succession with seams. The Productive Coal Measures comprise phosphatic nodules. Further south,there may be cyclicsedimentary sequences which ideally an important break in the sequence since some of compriseinitial grey and dark grey mudstones. thegoniatite zones areunrepresented (Jones and Theseare followed by: siltstones; a yellowish Lloyd, 1942; Ramsbottom and others, 1978). brown,feldspathic, cross-bedded sandstone; a GwespyrSandstone Thissandstone occurs at the seatearth (fossil soil), and coal. The coal is then top of theformation and its distribution is succeeded by the mudstone at the base of the next complex. It comprises up 150 to m of cycle. Mudstone is thedominant lithology of the buff-coloured, feldspathic, medium- and cycles. Bands of dark greymudstone, which fine-grained, cross- bedded sandstones with usually occur immediately above the coals, contain varying interleaves and intercalcations of siltstones marine fossils includingstratigraphically and mudstones. It is Yeadonian in age. Its diagnostic goniatites. Non-marine bivalves are thickestdevelopment is inthe north and this is also used in correlation. consistent with current direction data suggesting a Thecyclicity of thesediments demonstrates a northerlysource. In most areas, mudstones systematicpattern of subsidenceand infill of the containingthe Subcrenatum Marine Band, which basin within which they accumulated. The overall is used to delineate the top of the Namurian/base sedimentaryregime ofwas fluvio-deltaic of the Westphalian (Coal Measures), occur sedimentation in shallow brackishwater with immediately above the Gwespyr Sandstone. In the occasional marineinfluxes. The sandstones were east of thearea, south of Hawarden,the depositedboth by sheet-floodsand by migrating SubcrenatumMarine Band occurswithin the channels. The coals representcondensed sequence of feldspathicsandstones and the term vegetation which accumulated in stagnant swampy Gwespyr Sandstone is restricted to the strata conditions,whereas the seatearths which underlie underlying the marine band. themreflect soils inwhich vegetation flourished, but without accumulating a coal. Coal Measures (Westphalian) as A correlation of theprincipal coal seams within Inthe British Isles, it is common practice to the area is given in Figure 12. subdividethe Coal Measures in terms of the biostratigraphy (i.e. fossil content)rather than Westphalian A Few of the standard goniatite zones lithostratigraphy(variation of rocktype). Thus, of Westphalian A are represented.The exceptions elements of the sequencereferredare to arethe Subcrenatum Marine Band which marks Westphalian A, B, C, and D. Though questionable the baseof Westphalian A and lies about 20 m as a method of depicting stratigraphy within what above the Gwespyr Sandstone in the north of the is otherwiselithostratigraphic a context, the area (Shanklin 1956), and the Listeri Marine Band

82 Deeside(North Wales) Thematic Geological Mapping whichoccurs approximately 30 mhigher, and Buckley Formation (=Buckley Fireclay Group of immediately above the Chwarelau coal seam. Calver and Smith, 1974) Thisformation (maximum thickness >190m) is Strata of Westphalian A agevary in thickness intermediatein character between the Productive from 160 m in the south of the area to 230 m in CoalMeasures andthe Ruabon Marl (see below). thenorth. The principal coal seams are,in It is well exposed in large ‘fireclay’ quarries in the ascending order, the Chwarelau, Llwyneinion Half Buckley area where it comprises pale and pinkish Yard,Premier, Ruabon, Yard, Nant, Nine Foot, grey,quartzose sandstones and siltstones, and NineFoot Rider, Stone(or Wall and Bench). grey,red, maroon and purple mudstones and Lower Red(or Cannel), and the Upper Red (or seatearths.Rare fossils indicatea WestphalianC King). Seam splitting of the Stone andLower age (Wood, 1937). The transitionfrom the Red occurs in the north of the area. The thickest Productive Coal Measuresto the Buckley of the seams arethe Premier (0.45-2.1 3m), the Formation is complex,sinceBuckleythe Nant (0.48- 1.93 m), the Wall and Bench(locally Formationappears at varying stratigraphic levels upto 4.14 m)and the King (0.35- 1.8 m). The atdifferent places inthe area. Thus, inthe NineFoot and the Nine Foot Kider are more vicinity of Ewloe (SJ 285 655), it occurs as low as variablein thickness and distribution but attain the Black Bed coal(Westphalian B) but elsewhere thicknesses of 2.87 m and 3.0 m respectively. its base is recordedhigherat levels upto Westphalian B The base of Westphalian B is taken Westphalian C (i.e. representing 110 m of the as the Marine Band which overlies the Upper Red sequence).Thisrelationship mightsuggest Coal. WestphalianB varies in thickness from c. unconformitybut it is consideredhere to be a 80 min the Mold areatoc. 150 maround lateralfacies change, shifting position with time Eiagillt. Theprincipal coalseams arethe Crown untilthefacies of the BuckleyFormation (or Diamond), Lower Bench, Main, Black Bed (or eventually extended across the whole area. Rough),Quaker (orBrassey), Crank, Hollin, RuabonMarl Powell (orBind), and the Drowse11 (or Massy). Thisformation (up to 120 mthick) comprises TheMain is consistentlythethickest seam predominantlyred, brown and purple mudstones, (1.8-4.5 m) of theProductive Coal Measures in thin siltstones andsandstones, with rare thin thearea. With theexception of the Hollincoal limestones,some thin coals and somegrey (0.7-2.75 m), theother seams are generally less mudstones.The sequence is poorlyknown due to thanmetre1 thick and are not as laterally lack of exposure.It is recognisedonly inthe continuous as seamsWestphalianin A. Seam northeast of thearea and around Flint. These splitting of the Crown occurs in the north of the sedimentswere probably laid down in shallower area. brackishwater than most of theProductive Coal Westphalian C The base of Westphalian C is Measures. Their age is poorlyconstrained due to considered,arbitrarily, to lie atthe base of the alack of fossils but is thought to be Westphalian Hollin Rock,a thick, feldspathic, cross-bedded, (Calver DSmith,and to C 1974). An medium-tofine-grained sandstone. It has a unconformity is inferredherebetween the transgressive,erosive base and rests at various RuabonMarl and lowerbeds (Buckley Formation horizonsabove the Hollin, Bind and Massy coals. and Productive Coal Measures), but the possibility The Hollin Rock is thickest in the south where it of there beinga lateral facies change inpart (cf. is up to 70 m thick, and thins to the north where, CalverandSmith, 1974) betweenthetwo around Bagillt andFlint, it is about 10 mthick. formations has notbeen ruled out. AtFlint the Relativelyfew and only thin coal seams occur. unconformity or facies change cuts down to below Thethickest development of Westphalian C the Main coal. ProductiveCoal Measures is 150 aroundm Buckley. In the northeast and around Mold in the Permo-Triassic southwest,there may be none, as theBuckley Kinnerton Sandstone Formation Formation (see below)succeeds Westphalian B directly.the In Bagillt andFlintareas, Strata of Permo-Triassicage (between 280 and Westphalian C is represented respectively by the 210 millionyears old) overlie theCarboniferous Hollin Rockalone, and 30 m of strataincluding rockswith pronounced angular unconformity. the Hollin Rock. Theunconformity is onlypoorly exposed now at onelocality in the southeast [SJ 3275 60221, south of HigherKinnerton, but it was describedin Deeside (North Wales) Thematic Geological Mapping 83 detailin days of betterexposure (Hull, 1869). The dominant synclinal and anticlinal structure of TheKinnerton Sandstone Formation rests onthe thearea (see ThematicElement, Map 1 - Cross GwespyrSandstone (Halkyn Formation) at this section)reflects theextensional basin within locality. Further north, it rests on various levels whichthe Carboniferous was deposited.Many of of theProductive Coal Measures (Westphalian A thedominantly N-S andconjugate E-W faults and B). It is very poorly exposed, underlying were probably generated during the Carboniferous thicksuperficial deposits on the edge of theflat extensional,normal faults related to the Plain. Where exposed, andproved in as formation of the basin. Someof these faults may boreholes, it comprises brownishred and yellow, also have had a strike-slipcomponent. There is cross-bedded, fine- to medium-grained sandstones littleevidence to constrain post-Westphalian (up to 300 m thick within the area). faulting. End-Carboniferousfaulting. movements (Hercynian)are likely to have occurredbut have ? Tertiary not been differentiated. Also, as many of the Solution pipes within the Carboniferous Limestone faultsare sub-parallel to themain faults west of areinfilled at several localities with redand the area which bound the Vale of Clwyd graben, brown sands, siltsand clays, thought to be of which is aPermo-Triassic basin, activation and, Tertiary age (Walsh and Brown, 1971). or,reactivation of these faults seems likely to have occurred at that time. Structure Thestructure of thearea is dominated by major Mineraiisation faultstrending NNE-SSW and N-S. They have The locally intense lead, zincandcopper downthrowcomponents to both east and west. mineralisationoccurswhich mainly in Theydefine horsts and grabens in the coalfield CarboniferousLimestone rocks was influenced (? area. Amajor fault of thisorientation, the Nant controlled) by the NW-SE, E-W and NE-SW FigilltFault (Strahan, 1890), causes markeda faultsand joints. In the south of thearea, there offset of the Carboniferous Limestone and is virtually no mineralisation associated withthe Namurianoutcrop in the vicinity of Rhosesmor N-S ‘cross-courses’. Furthernorth, however,and [SJ 214 6841. Althoughits apparent displacement north of theNant Figillt Fault, extensive is a downthrow (c. 275 m)to the WSW, the fault mineralisation is associated with N-S faults may have an important dextral strike-slip (lateral) (particularlyinthe area immediately south of component. As theCarboniferous Limestone and Holywell). The WNW-ESE faultssouth of Namurian sequences differ markedly across the Holywell are also extensively mineralised. fault,it is probablethat the fault was active The mineralisation occurs mainly as discontinuous duringtheir deposition. Open, periclinal folding veins (? solutioninfills) along faultsand joints, , in its vicinity is probably related to movement on but it also occurs in steep pipes (probably infilled thefault. Further south, an en echelon of fault solution pipes) and along selected bedding planes even greatermagnitude, but with aneasterly (‘flats’) (see Smith, 1921). Thechief ore is galena downthrow of up to 700 m and possibly more, has (lead sulphide), with sphalerite (zinc sulphide) and been invoked.juxtaposesIt the Buckley and minoramounts of chalcopyrite(copper, iron Halkyn Formations. A pronouncedgravity sulphide).The main associated veinmineral is anomaly associated withthis fault (Cornwell, is calcite,with minor amounts of zinc and lead 1987). A furtherimportant fault of similar carbonate. orientationruns along the Wheeler Valley inthe westof thearea, and downthrows to the west. Most of themineralisation occurs within the Faults ofNNW-SSE and N-S orientationare upperpart of the Loggerheads Limestoneand in referred to as ‘cross-courses’ in the mineralised Cefnthe Mawr Limestone. Many of the district in the west of the area. mineralised faultstheinupper Loggerheads Limestone splay upwardsinto many faults with The Carboniferous Limestone outcrop is disrupted lesser displacement close to the boundary with the by numerous faults of a general E-W orientation. Cefn Mawr Limestone. South of the NantFigillt As theoutcrop is traced from south to north, Fault, there is little mineralisation above the level these faultsswing from NW-SE through E-W to of the ‘Main shale’ inthe Cefn Mawr Limestone. NE-SW inthe area south of Holywell. A set of North of the NantFigillt Fault, mineralisation WNW-ESE faults occurs south of Holywell with extends up intothecherts of the Halkyn downthrow to the south. Formation. 84 Deeside(North Wales) ThematicGeological Mapping

freeze-thawconditions of immediatethe Thenature and stratigraphic distribution of the postglacial era, glacial deposits suffered downslope ores suggest thatthey were precipitated in mass-movement by solifluction processes solution. voids withinthe limestone and producinghead deposits. Landslip also occurred particularly along pre-existingfaults.The at thistime, both inbedrock andsuperficial stratigraphicrestrictions probably reflect the deposits, and it persists to the present time. Some optimumconditions forprecipitation of the of themajor pre-glacial valleys, andparticularly mineralising fluids (e.g. pH). the Wheeler, Alynand Dee valleys, were largely infilled by glacial deposits; thethickness of Quaternary superficial deposits in the infilled Dee Valley may Thearea was affected by glaciationduring the locally exceed 90 m. Flood conditions continue to Quaternary,but only evidence of thelater stages infillthe valleys withalluvial deposits and of glaciation(Devensian) has been preserved. estuarinealluvium is accumulatingin the Dee Glaciation affected a post-Triassic erosion surface Estuary.Part of the Dee Estuary has been andaccentuated existing valleys. Inaddition new drained in recent times. dissections werecaused by subglacial and periglacial processes. Ice-sheets from two directionsimpinged on the area, one fromthe direction of northand central Wales (the ‘Welsh’ ice-sheet) and the other from the Irish Seato the north (‘’ ice-sheet). These ice-sheets merged inthe vicinity of the Alyn River (Ball and Adlam, 1982; Thomas, 1985). Extensive basal tills (boulder clays) were deposited.The two different ice-sheetsources are reflectedin the different clast compositions of the two till deposits. The ‘Welsh’ ice-sheet till comprises grey clays with clasts mostly of Lower Palaeozoic cleaved siltstones and sandstones, vein quartz and acidic volcanic rocks. The ‘Irish Sea’ ice-sheet till comprises reddishbrown clays withabundant clasts of CarboniferousLimestone, mudstone, sandstone, chertand coal of local derivation,in addition to Triassicsediments andgranitic, volcanic, metamorphicand vein quartz clasts of more distant provenance. Subglacial drainagechannels, particularly related to the ‘Irish Sea’ ice-sheet, have been recognised (Peake, 1961). Thickfluvioglacial deposits were deposited along the Alyn and Wheeler riversand more extensive sheets occur to the north of Mold. Further depositsoccur as ‘terraces’ along the southwestside of the Dee Estuary.These fluvioglacialdeposits are of both subglacial (Brown and Cooke, 1977) and proglacial lacustrine origin (Peake, 1961; Thomas, 1984), the latter relatedparticularly to retreat of the ice-sheets. Minorice-sheet readvance occurred resulting in local interdigitation of till andfluvioglacial sand and gravel. During glacial retreat, patches of dead ice were leftand the melting of these producedkettle holes (depressions) in the sand andgravel deposits. These were sites of small lakes and ponds andlaminated clay and peat accumulatedwithin them. theIn Periglacial Deeside (North Wales) Thematic Geological Mapping 85

CONCLUSIONS AND RECOMMENDATIONS 1e.There is only localised andgenerally limited superficial overburden. New geological maps anda revised stratigraphy have been produced forthe Deeside area. These 1f. There is considerable scope for deepening provide the basis for thematic geological maps and existingquarries. All existingquarries are in assessment of resources, geological hazards, upper levels of the limestone sequence with at geotechnical properties and hydrogeology. least 200 m of limestone underlying them. Geological conclusions are presented in the 1g.The Halkyn-Holywell drainagetunnels (and context of: particularlythe Milwr sea-level tunnel) could A. Resource potential and future extraction have animportant role to play infuture deep-levelquarrying by reducingthe level of B. Geological problems andhazards C. Engineering properties and problems thewater-table and providinga direct means of drainage. D. Hydrogeology and water supply 1h.The mainrestrictions forfuture limestone A.Resource potential and future extraction extraction are likely to be: The main economic resources of thearea are i) The height of the water-table. limestone, sandand gravel, and coal. Of these, ii) Areas of sterilisedground due to housing only limestone andsand and gravel arecurrently and roads. exploited.Other significant resources which have been exploited are metalliferous (lead, zinc and iii) Areas of former intensivemetalliferous copper)ores, chert, feldspathic and quartzitic mining in limestones. sandstones, mouldingsand, and brickclay and refractoryclay. Minor cementstone, calcspar and iv) Theoccurrence of two Sites of Special Scientific Interest situated on the limestone peat deposits have been exploited. outcrop. , A.1 Limestonequarrying - v) Environmentalconsiderations in areas of natural beauty. la. Limestone is volumetricallythe most significantresource and supports the largest vi) Theeffect of extraction on the local extractiveindustry of thearea with 7 large topography. working quarries. vii) Theeffect on local land use (principally 1b.Limestone crops out overapproximately agriculture). 39 km2 along the western side of the area and continues at depth beneath the area east of the Henceonlya small proportion of the outcrop. The theoretical resource within the theoretical resource is likely to be available for extraction. Currentextraction removes area of outcrop and above Ordnance Datum is approximately 0.01 to 0.02% of the maximum approximately 2.75 x 10" tomes. Less than resource per annum. 1% of this resource has been extracted. lc. New subdivision of the limestone sequence and A2. Sand and gravel extraction itsdetailed mapping provide arational basis 2a.Available sand and gravel resources atsurface forfuture extractionandconstrain the and beneathand limited overburden cover distribution of limestones with different approximately 43 km2. characteristics (e.g. aggregate potential). These characteristicsare directly related to 2b.Deposits arepatchily distributed across the grain size andare readily recognised interms area, concentrated: of theDunham classification (i.e. calcite i) Along or nearthe Alyn and Wheeler rivers. mudstone to grainstone). ii)North of Mold. 1d.The greaterpart of the limestone outcrop is suitable for aggregate andcement making. iii) Along thesouthern andsoutheastern side Interbedded shale andsandstone are generally of the Dee Estuary. restricted to theupper part of the sequence. 2c.Despite thelarge area of theresource, the Small, local, clay and sand-filled solution pipes deposits arerelatively thin,rarely exceeding occur. 30 m. The maximum theoretical resource is 86 Deeside (North Wales) Thematic GeologicalMapping

estimated at 5 to 7.5 x lo8 tonnes. 3d.Records suggest thatapproximately 20 km2 of 2d.As theresource is relativelythin, large areas thearea is undermined.Older, unrecorded need to be excavated to producesignificant workings significantly increase this area but no estimate is possible. volumes of aggregate. 2e.Large areas of the resource (>lo%) have been 3e.Records of working indicate that up to 30% of sterilised by urbandevelopment (e.g. Mold, major Westphalian B seams (including the Main Bagillt, HawardenGreenfield),and and and Hollin coals, the most extensively worked and consistently thickest seams) and up to 15% approximately 2% of theresource has already been extracted. of major Westphalian A seams have been substantially worked. representsThis 2f. Deposits varyrapidly in thickness and grain approximately 20% of the theoretical coal size, particularly inthe case of thecoarser resource. gravelfraction. This variation is hard to 3f.A wide range of extraction techniques has been predict. used includingopencasting, adits, bell pitsand 2g.The clast contentin the southwest is radically deep mining (via shafts) by pillar and stall and different from that elsewhere, being dominated longwall methods. Recordsare insufficient to by siltstone and greywacke. define depths of workings or methods used. 2h.The most common sand and gravel type in the 3g.The Coal Measures are extensively faulted and area is dominated by locally derivedrock structurally complex, muchreducing any

types, including coal. ’ Unpredictable potential for future economic deep mining. concentrations of coal are problematicsince 3h.The main limitingfactors for opencast mining theyreduce the quality of the resource for are: aggregate use. Thegenerally thick superficial deposits 2i.As many of the depositshave a pronounced, i) coveringthe Productive Coal Measures, moundy topography, their removal would have except around Buckley. significantenvironmental impact. Depressions (kettle holes) betweenthe mounds are locally ii) The presence of bedrockoverburden clay and peat filled to considerable depth, thus lackingsignificant coal seams over reducing the resource potential of some areas. substantial areas of the coalfield. 2j.The available sand and gravel resource is iii) Structural complexity. considerably smaller than that of limestone and iv) The unpredictability of thickness variations of extractionrelative to limestone itsrate and washouts of the coal seams, andthe should be carefully considered by planners and apparentlateral passage from Productive developers. Coal Measures intobarren strata (the Buckley Formation and Ruabon Marl). A.3 Coal mining and opencasting Earlier unrecorded mining of the principal 3a.Coal is substantial a resource, with coal v) seams. seams underlyingapproximately 132 km2. Westphalian B seams underlie 65 km2 of this vi) Urban sterilisation of resources. area. vii) Environmental considerations. 3b.Records indicatethe mining of20 different coal seams thein area. No mining or A.4 Other extractive industries opencasting is current,though planning Limited resources of chert, metalliferous deposits, permission has recentlybeen sought to renew sandstone, and brickclay occur. opencasting. 4a.Metalliferousmining - Ores arerestricted to 3c. The ‘theoretical’ coal resource, (before allowing veins, joints, pipes and some bedding planes in for coal alreadyextracted), assuming an thelimestone and chert terrains. Their spatial averagetotal coal thickness for Westphalian A restrictions,unpredictable concentration and and B seams of 10 mand 9 m respectively, is theextent of past extractionat shallow levels estimatedat 3 x lo8 tonnes. Two thirds of the preclude furtherextraction in volume under resource occurs in Westphalian A strata. present and foreseeable economic terms. Deeside (North Wales) Thematic Geological Mapping 87

are rarely known. 4b.Chert - Chert is alimited resource. Deposits arestructurally complex. As chert is an B.2 Coal mining uncommon resourcenationally, possible future demand should be considered. 2a. More than 1000 shafts and adits related to coal mining have been recorded. 4c.Sandstone - Various types occur but scattered distribution precludes major extraction in most 2b.Only a small proportion of shaftsare capped. areas. Poorly cemented Triassic sandstone is Collapse has been recorded at severalshaft worked on a small scale for moulding sand and sites. other purposes. 2c. Unrecordedshafts and underground workings 4d.Brickclay andrefractory clay occursin may be presentanywhere within the moderatequantity inthe Buckley area,where Productive Coal Measures outcrop. onesite is currentlyworked, and possibly 2d.Shallow workings must be anticipatedin any beneaththick superficial deposits, west of Mold and at Bagillt. part of theProductive Coal Measures outcrop andparticularly near the crops of thethicker 4e. Otherresources (calcspar, cementstone,peat) seams (e.g. theMain and Hollin coals) and are very localised and small-scale. where superficial deposits are thin. 2e.There is little evidence of active subsidence in B. Geological problems and hazards the 20% of thearea of the Coal Measures Few parts of thearea are unaffected by some known tobe undermined.Recorded collapse is form of quarryingor mining. Natural hazards generally associated withshafts. This may also occur. reflectthe lengthy period since mostof the workings were abandoned.Furthermore, thick B.1 Shafts and underground workings related to superficial deposits would subduethe effects metalliferous mining of subsidence ate .depth. Collapse associated with longwall mining is likelyalready to have la.In excess of 5000 shaftsand trial pit sites occurredin the main part. Unrecorded pillar related to metalliferousmining were identified andstall workings, particularly at shallow on thelimestone terrain. Only a small level, would pose the biggest possible threat of proportion of these have been capped. subsidence and ground stability problems. 1b.Uncappedshafts pose problems anddangers sincethey may appearfilled at surface while B.3 Quarrying being openat depth and are thus liable to 3a. Numerous quarries (active and disused) occur, collapse and reopening,particularly if mainly in limestone,sandstone, chert and disturbed.Active collapse was recorded at brickclay. several sites. 3b.Someof quarriesthe floodedare to 1c.HalkynMountain is the most intensely mined considerable depth (particularlythe brickclay part of the area. Although many shaftshere quarries near Buckley). have been capped, many remain open. 3c.Many have unstablesteepand faces 1d.A list of some openshafts has been prepared (particularlychertquarries).the Secure (Appendix E) but any uncapped shaft must be fencing is important. regarded as potentially unstable and dangerous. Evencapped shafts where unfilled may be 3d.Many are used as rubbish tips and, as most are affected by collapse. in rocks which are themajor aquifers of the area,protection from thedumping of soluble 1e.In addition to recorded shafts, others are likely toxic waste is important. to exist of which there may be little or no surface evidence. B.4 Waste tips 1f. The practice of persons bulldozing areas of Waste tips ofall kindsare liable to instability shafts to recoupfarmland is ineffective in though major problems have not been identified. removing hazardsand resolves the problem at surface only, not at depth. 1g.The extent and depth of underground workings 88 Deeside (North Wales) ThematicGeological Mapping

B.5 Landslip and poorlyconsolidated ground depthsup to 5 fromm surface. 5a.Active andrecent landslip was recognised at iii) Cuttingsin shaly limestone must not be several sites. steeper than 1:l. 5b.Many ancientand apparently stable landslips iv) The limestone is generally a suitable fill. wererecorded. These could however be reactivated if disturbed. 1b. Sandstones 5c. Althoughmany landslips occurin superficial i) Three categories sandstoneof were deposits, othersoccur in bedrock,most considered; Kinnertonthe Sandstone commonly along steep valley sides inthe Formationwhich is generally highly to HalkynFormation Productiveand Coal moderatelyweathered; sandstones in the Measures. Ruabon Marl; and sandstones thein ProductiveCoal Measures and the Halkyn 5d.Local peat andclay-filled kettle holes occur which would be unsuitable for foundations. Formation. ii) If the sandstones inthe Ruabon Marl are 5e.Dissolution of the limestone causes cavities to used a pile foundation in the vicinity of develop. Some are open thesurfaceat as theDee Estuary, there is likely tobe (swallow holes). They locally coalesce to cause contactbetween the in situ concrete piles substantialareas of foundered ground. The and saline waters. Caremust be taken also solution cavities are infilled to varying extents to determine the nature of strata below the with clay, silt and sand. pile founding depth to avoid the possibility of over-stressing any mudstones or shales. C. Engineeringproperties and problems IC. Mudstoneand shales The coverage of geotechnical data for most of the bedrockformations is poor(except forthe i) Three categories of mudstone/shalewere mudstones and shales of theHalkyn Formation, considered. All arecharacterised by very BuckleyFormation Productive and Coal variable weathering zones (up to 6 m depth Measures), whereas thatforthesuperficial fromsurface and possibly greater). When (unconsolidated) deposits is reasonably weathered,they can be classified as clays comprehensive. The available geotechnical of low to intermediateplasticity and low properties of all ofthe bedrock formations and compressibility. Strength is inversely superficialdeposits have been reviewed and proportional to weathering, and weathering summary tables prepared, synthesising datafor tends to increase where cover of superficial 4273 individual samplescovering up to 16 deposits is less. geotechnical tests and measurements(laboratory ii) Forsites along the Dee Estuary(and andsitu).in Onlyain small minority of elsewhere), piles should be takenthrough instances has thefull rangeof tests beencarried theweathered zone (at least 3 m, though out. Maximum nettsafe bearing pressures have this is dependent on the site) into the hard been quoted where available. mudstone/shale beneath. C.1 Bedrock, engineering properties and problems iii) Landslips occur in several areas, particularlywithin the Halkyn Formation. 1a. Limestones Failure planes appear to be in highly i) Three categories of limestone were weatheredmudstones or shales. Where considered, reflecting to a large extent the slopes are greater than approximately 7O on relativemudstone/shale content. The these shales, carefulinvestigation must be limestones are generally strong but mass made to determine if any slope movement strength is affected bymudstone/shale has taken place and to check the effect on layers, their thickness andseparation, and any proposed structure. jointing.Open or infilled cavities present iv)Confirmation should beobtained that an engineering hazard. weatheredmudstone or shale horizons are ii) Rockhead is very irregular because of open not presentwithin the stressed zone jointingandfracturing. Thus ripping beneath the piles. without blasting wouldbe practicable for v) As themudstones and shales softenon Deeside (North Wales) Thematic Geological Mapping 89

contactwith water, excavations should be verticalexcavations require shoring and protectedagainst wetting and they need excavation activity should avoid peak tides. supporting.Precautions may have to be v) Safebearing pressures are low butincrease taken to prevent weathering and swelling. withdepth, and therefore piling to these vi) Themudstones and shales areunsuitable densermaterials atdepth will be more forfill, unless no alternative is available reliable. Depths of foundationsare and then they should only be used for low thereforecritical to theirstability. The embankments. clays have very low safebearing pressures and highcompressibility and aretherefore C.2 Superficial (unconsolidated) deposits, generallyunsuitable for light-weight, engineering properties and problems single-storey structures, whereas the sands have higher safe bearing pressures. 2a. Backfill and made ground vi) Goodquality dense cement must be used i) These are veryvariable andare generally below the water- table. unsuitable for the support of light-weight, single-storey structures. vii) As the deposits areheterogeneous, and variably compressible, large settlements can ii) Thereii) is a possibility of sulphate occur (even with small loads) and contamination from these deposits. differential subsidence is a possibility. 2b. Peat 2e. Lacustrine Alluvium i) Peat is highly compressible, and has high As it comprises soft to stiffcompressible clays, moisturecontents andAtterberg limits. problems of stabilityand settlement would be Consequently,there is a need to avoid anticipated. structures being founded on it. 2f. Heterogeneous deposits(Head) 2c. Alluvium i) Alluvium is relatively heterogeneous. Headi) is veryheterogeneous. Relatively Therefore,foundation problems arevery thin veneers areextensive and deposits site-specific. occur not only at the surface. ii) Generally low maximumnettbearing ii) Geotechnicalcharacteristics veryare pressures have been quoted,making it variable. problematic for support the of iii)Perched water-tables may occurand there light-weight,single-storey structures is the possibility of runningconditions in without piling, though gravelly layers show excavations. much higher bearing pressures. iv) Deposits may containshear planes, and 2d. EstuarineAlluvium increasedpore pressures, undercutting of i) It is relativelyheterogeneous though less slopes, or loading at the top of slopes may coarse-grainedmaterial occurs thanin activate(or reactivate) movement causing other alluvium. failure.Therefore, care must be taken to ii) It variesfrom Itverysoft,highly ii) examine slopes (even of only few a degrees) forshear planes and solifluction compressible low strength clay to loose, generally saturated sand which increases in lobes. Piles may be necessary intostronger underlying strata. densitywith depth. The deposits broadly coarsen with depth and away from estuary 2g. Glacial Sand and Gravel margins. i) These deposits arevery heterogeneous and iii) Being low-lying, the water-table is near (or may be stratified.Therefore differential '

' at)surface, the sedimentsaresaturated settlementproblems may occur. Maximum (withmoisture contents for the clays safebearing pressures reflect the gravel approachingliquid limits) and there is a content to a large extent. risk of running conditions. ii) Deposits areprone to running,and iv)Excavations require groundwater control excavations will deterioraterapidly. Thus (e.g. well-pointdewatering, pumping etc.), theyrequire shoring and slopes should be 90 Deeside(North Wales) ThematicGeological Mapping

back tocut back 1:l. CarboniferousLimestone D.2 iii)Groundwater problems are likely, with 2a.This is thesecond most importantaquifer in highwater flows in coarser material. High the area. hydrostatic pressures can occur. 2b.Drilling waterfor within it is highly iv) Safeiv) bearing pressures arevery speculative as groundwatermovement is largely site-specific.There is danger,a clayif restricted to fissuresenlarged by solution, bandsare present, of heavingand sagging which arehard predict.to Groundwater just belowthe depth of movementthe can be rapid. site-investigation. 2c.Tunnelsassociated with old mineral workings Till (Boulder Clay) have had a significant effect on the onsignificant effect a had have (Boulder2h.Clay) Till hydrogeology Theof area. the i) are very heterogeneous and Halkyn-Holywellminedrainage scheme has geotechnicalproperties are very variable, been used for water supply. reflectinglithology, depth and weathering. Differentialsubsidence maybe a problem. 2d.The quality of waterderived from the limestones is generallyhard, but good. Metals ii) Higher nett safe bearing waterpresentwheretheare has been in pressures Occur at depth, but softer contactwith oldmineral workings. horizons may not support piles. iii)Sloping of sitesreduces expected safe 0.3 Sandstones in the Halkyn Formation bearing pressures. 3a.Only one small yield is recorded in the area. iv) Perched water-tables may occur. 3b.Thewater is of good quality,but hard. . Iron v) Clays are liable to softening on exposure to may, however, be a problem. rain. Therefore,excavations should be protected,supportedand ensure to 0.4 Sandstones in Westphalian strata stability. 4a.Water occursparticularly within joints and vi) Atnatural moisture content, till is a fractures caused by mining subsidence. suitable fill deposit. 4b.Yields of water from boreholes arerarely D. Hydrogeologyand Water Supply sustainedsincerecharge is limited by separation of theaquifers into fault-blocks, Thereare several groundwater abstractions for andbecause of theextensive cover of low public supply and industrial purposes, but most of permeability superficial deposits. thewater used comes fromoutside the area. As groundwater commonly receives little treatment, it 4c.Thequality of water is variable,but usually is importantthat aquifers are protected from non-potable. Wateris oftenpolluted by potentialpollutants. Twomain sources of mining activities. pollution arepoint sources (e.g. landfilland waste disposalsites) and diffuse sources (e.g. agriculturalfertilisers and biocides). However, theserepresent little risk to groundwaterquality overmuch of thearea, due to theextent of impermeable superficial deposits.

D.I Kinnerton Sandstone Formation 1a.This is the major aquifer in the area. 1b.It is beingpredominantly recharged from east of the study area. 1c.Thequality of waterderived from it is good, but hard. Deeside (North Wales) Thematic Geological Mapping 91

REFERENCES CORNWELL, J D.1987. Gravity anomalies associated with the Cefn-y-Fedw Sandstone ANON. 1972. The presentation of maps and Group, northeast Wales, and their geological plans in terms of engineering geology. Working significance. Geological Journal, 22, 261 -272. Party report. Quarterly Journal of Engineering Geology, 5, 293-381. DAVIES, J R, RILEY,N J and WILSON, D In press. The distribution and significance of BALL, F and ADLAM, K A McL. 1982. 6 Chadian strata in north Wales. Geological Journal. The sand and gravel resources of the country around Mold, Clwyd. Mineral Assessment Report, DEERE, D. 1964. Technicaldescription of cores Institute of Geological Sciences, 1 13, 63pp. for engineering purposes. Rock Mechanics and Engineering Geology, 1, 18-22. BANERJEE, A. 1969. Carboniferouslithofacies, Rhydymwyn to Erryrys, North Wales. Geological DUNHAM, R J.1962. Classification of Journal, 6, 181 - 184. carbonate rocks, according to depositional texture. Memoir of the American Association of Petroleum BARTON, N, LIEN, R andLUNDE, J. 1974. Geologists, 1, 108- 12 1. Engineering classification for rock masses for design of tunnel support. Rock Mechanics, 6, EMBLETON, C.1970. North-eastern Wales. In: 189-236. Lewis, C A (editor). The Glaciations of Wales and Adjoining Regions. Longman, London, 59-82. BIENIAWSKI, Z T. 1974. Geomechanics classification of rock masses and its application in GEOLOGICAL SURVEY OF GREAT BRITAIN. tunnelling. Proceedings of the 3rd International 1920a. Special Reports on the Mineral Resources Congress of Rock Mechanics, 2, 27-32. of Great Britain. Vol.VI - Refractory materials: International Society of Rock Mechanics, Denver. Ganister and silica-rock - Sand for open-hearth steel furnaces Dolomite. Memoir of the BRITISH STANDARDS INSTITUTION. 1972. - Geological Survey of Great Britain, 241 pp. Code Of practice for foundations. C.P. 2004. H.M.S.O., London. GEOLOGICAL SURVEY OF GREAT BRITAIN. 1920b. Special Reports on the Mineral Resources BRITISH STANDARDS INSTITUTION. 1975. of Great Britain. Vol XIV - Refractory materials: Methods of test for soils for civil engineering Fireclays. Memoir of the Geological Survey purposes. B.S. 1377. H.M.S.O., London. of Great Britain, 243pp. BRITISH STANDARDS INSTITUTION. 1981. GEORGE,T N.1974. LowerCarboniferous Code of practice for site investigations. B.S. 5930. rocks in Wales. In: Owen, TR (editor). The H.M.S.Q., London. Upper Palaeozoic and post-Palaeozoic rocks of BROWN, E H and COOKE,R U.1977. Wales. University of Wales Press, Cardiff, Landforms and related glacial deposits in the 85-115. Cambria, Wheeler Valley area, Clwyd. 4, 32-45. HARRISON, D J,MURRAY, D W and WILD, BUILDING RESEARCH ESTABLISHMENT. J B L. 1983. Reconnaissance Survey of 1975. Concrete in sulphate bearing soils and Carboniferous Limestone resources in Wales. groundwaters. Digest 174. H.M.S.Q., London. Institute of Geological Sciences, Keyworth, 79pp. CALVER, M A and SMITH, EG. 1977. The HEAD,K H.1982. Manual of soil laboratory Westphalian of North Wales. In: Owen, T R testing. Pentech Press, London. (editor), The Upper Palaeozoic and HIND, W and STOBBS, J T. 1906. The post-Palaeozoic rocks of Wales. University of Carboniferous succession below the Coal Measures Wales Press, Cardiff, 169-83. in north Staffordshire, and CLWYD COUNTY COUNCIL. 1981. North Flintshire. Geological Magazine, 43, 387-400, Wales Working Party on Aggregates. Regional 445-459, 496-507. Commentary, Parts I and II. HULL, E.1869. TheTriassic and Permian rocks CLWYD COUNTY COUNCIL. 1982. CZwyd of the midland counties of England. Memoir of Structure Plan. Ihe Geological Survey of Great BritaiH, 127pp. JACOBS, CA J. 1982. MineralWorking in Clwyd'. Clwyd County Minerals Plan, Final Draft Written Statement. 155pp. 92 Deeside(North Wales) Thematic Geological Mapping

RAMSBOTTOM, W H C. 1974. TheNamurian JONES, RC B and LLOYD, W. 1942. The in North Wales. In: Owen, T.R. (editor), The stratigraphy of the Millstone Grit of Flintshire. Upper Palaeozoic and post-Palaeozoic rocks in Journal the Geologists Association, of Wales. University of Wales Press, Cardiff, 16 1-7. 1, 247-62. RAMSBOTTOM, W H C. 1977. Major cycles of LAMBE, T W Soil and WHITMAN,R V.1979. transgression and regression (mesothems) in the mechanics (S.I. version). Wiley,New York. Namurian. Proceedings of the Yorkshire MAGRAW,D andCALVER, M A.1960. Geological Society, 4 1, 26 1-29 1. Faunal marker horizons in the Middle Coal RAMSBOTTOM, W H C, CALVER,M A, Measures of the . EAGAR, R M C, HODSON, F, HOLLIDAY, Proceedings of the Yorkshire Geological Society, D W, STUBBLEFIELD, C J and WILSON, R B. 32, 333-52. 1978. A correlation of Silesian Rocks in the MARSLAND, A.1977. Theevaluation of the British Isles. Geological Society of London, engineering design parameters for glacial clays. Special Report, 10, 81pp. Quarterly Journal Engineering Geology, 10, of SARGENT, H C. 1927. Thestratigraphical 1-26. horizon and field relations of the Holywell Shales MAW, G. 1867. Onthe distribution beyondthe and "Black Limestone" of North Flintshire. Tertiary districts of white clays and sands Geological Magazine, 63, 252-63. subjacent to the Boulder Clay. Geological SHANKLIN, J K. 1956. New record of the Magazine, 4, 241 and 299. Gastrioceras listeri Marine Band in Flintshire. MORTON,G H.1870. Onthe Mountain Liverpool and Manchester Geological Journal, 1, Limestone of Flintshire and part of Denbighshire. 536-42. Geological Magazine, 7, 526-527. SIMPSON, B. 1940. The Salopian rocks of the MORTON,G H. 1886. TheCarboniferous , between the Gap and Limestone and Cefn-y-fedw Sandstone of Moel Llys-y-coed, Flintshire. Proceedings of the Flintshire. Proceedings of the Liverpool Geologists Association, 5 1, 188-206. Geological Society, 4, 297-320,381-403. SMITH, B. 1921. Special reportson the mineral NEAVERSON, E.1929. Faunal horizons inthe resources of Great Britain. Volume XIX - Lead Carboniferous Limestone of the Vale of Clwyd. and Zinc ores in the Carboniferous rocks of North Proceedings of the Liverpool Geological Society, Wales. Memoir of the Geological Survey of Great 15, 111-133. Britain, I62pp. NEAVERSON, E.1946. TheCarboniferous SOMERVILLE, I D. 1979. Acyclicity in the Limestone of North Wales: Conditions of early Brigantian (D2) limestones east of the deposition and interpretation of its history. Clwydian Range, North Wales and its use in Proceedings of the Liverpool Geological Society, correlation. Geological Journal, 14,69-86. 19,113. SOMERVILLE, I D and STRANK, A R E. OLDERSHAW, A E. 1969. Carboniferous 1984a. Faunal discoveries from Visean limestones lithofacies, Halkyn Mountain, North Wales. of North Wales. Proceedings of the Geologists Geological Journal, 6, 185- 192. Association, 95, 394-395. PEAKE, D S. 1961. Glacialchanges in the Alyn SOMERVILLE, I Dand STRANK, A R E. river system and their significance in the 1984b. Discovery of Arundian and Holkerian glaciology of the North Welsh border. Quarterly faunas from a Dinantian platform succession in Journal of the Geological Society, London, 1 17, North Wales. Geological Journal, 19, 85-104. 335-366. STRAHAN, A.1890. The geologyof the RA.MSBOTTOM, W H C. 1973. Transgressions neighbourhoods of Flint, Mold and . and regressions in the Dinantian: a new synthesis Memoir of the Geological Survey of Great Britain, of British Dinantian stratigraphy. Proceedings of 2 16pp. the Yorkshire Geological Society, 39, 567-607. THOMAS,G S P. 1984. A late Devensian glaciolacustrine fan-delta at Rhosesmor, Clwyd, North Wales. Geological Journal, 19, 125- 14 1. Deeside (North Wales) Thematic Geological Mapping 93

THOMAS, G S P. 1985. Thelate Devensian glaciation along the border of northeast Wales. Geological Journal, 20, 3 19-340. WALSH, P T and BROWN, E H. 1971. Solution subsidence outliers containing probable Tertiary sediment in north-. Geological Journal, 7, 299-320. WARREN, P T, , D, NUT", M J C and SMITH, E G. 1984. Geology of the country around and . Memoir of the British Geological Survey, sheets 95 and 107, 217pp. WEDD, C B andKING, W B R.1924. The geology of the country around Flint, Hawarden and . Memoir of the Geological Survey of Great Britain, 222pp. WOOD, A. 1936. Goniatite zones of the Millstone Grit Series in North Wales. Proceedings of the Liverpool Geological Society, 17, 10-28. WOOD, A. 1937. Thenon-marine lamellibranchs of the North Wales coalfield. Quarterly Journal of the Geological Society, London, 93, 1-22. WOODS, E G andCROSFIELD, M C. 1925. The Silurian rocks of the central part of the Clwydian range. Quarterly Journal of the Geological Society, London, 8 1, 170- 194. 94 Deeside (NorthWales) Thematic Geological Mapping

GLOSSARY CALCITE MUDSTONE A LIMESTONE similar ALLOWABLE BEARING PRESSURE The to a WACKESTONE, butin whichthe carbonate maximum allowable net loading intensityon the grain content must be less than 10% of the whole soil allowing for both shear and settlement rock ALLUVIUMDetrital material transported by a CALCSPAR Coarsely crystalline calcite, usually in river and deposited along its floodplain veins AQUIFER A body of rock that contains sufficient CALIFORNIA BEARING RATIO A standard test saturatedpermeable material to conduct for comparingthe strength of roadswith a GROUNDWATER and to yield economically standard material significantquantities of groundwater towells, CARBONACEOUS depositA that contains boreholes and springs organic matter ARGILLACEOUSdepositA containing an CEMENTSTONE A fine-grained CALCAREOUS appreciable amount of clay SILTSTONE or LIMESTONE ARTESIAN HEADThe hydrostatic head of an CHERT Arock comprising very fine-grained artesian AQUIFER, or of the water in the aquifer quartz ARTESIAN PRESSUREHydrostatic pressure of CLAST An individual grain or rock fragment artesianwater, or heightabove land surface of a column of waterthat would be supported by the CLEAVED Pertaining to a rock fabric imposed by pressure compression BASIN depression A whichin sediments COEFFICIENT OF CONSOLIDATION Therate accumulate atwhich volume changetakes place for a given increase in stress BEARING CAPACITY The load per unit of area which ~ theground can safely support without COEFFICIENT OF VOLUME COMPRESSIBILITY excessive yield Change inunit volume perunit change in effective stress BEDDING Thearrangement of sedimentarya rock in beds or layers of varying thickness and COHESIVE Asticky SOIL like clayey silt; some character authoritiesdefine it as a soil withan undrained shearstrength equal to half itsunconfined BEDROCK Geological strata at surface and below compressive strength SUPERFICIAL DEPOSITS COMPACTION TESTA test to determine the BIOCLASTICSEDIMENT Acomprising moisturecontent at which SOIL maybe fragments of SKELETAL material compacted to itsmaximum density; this is called BIVALVE A(fossil) mollusc with two shells the optimum moisture content which are symmetrical with respect to each other COMPRESSIBILITY Thereciprocal of bulk BLOWING Failure of STANDARD modulus PENETRATION TEST due to movement of CONGLOMERATE A coarse-grained sedimentary non-cohesive SAND around the sample tube rock with average clast size greater than 4 mm BRACHIOPOD A marine animal (fossil) with two CONSOLIDATION Reduction of bulk volume of symmetrical shells soil thatresults fromthe closer packing of BULK DENSITY The mass of anobject or particles caused by an increase in effective stress material divided by its total volume CORRELATIONThe process by which BURIEDCHANNEL An old channel concealed STRATIGRAPHIC units in two or more areas are by DRIFT deposits demonstrated to be temporally equivalent CALCAREOUSA deposit that contains calcium CRINOIDAmarine organism (fossil) witha carbonate structure comprising discs of calcite CALCITE A common rock-formingmineral, CROSS-BEDDING Structure in sedimentary rocks CaC03 comprising intersecting BEDDING PLANES Deeside (North Wales) Thematic Geological Mapping 95

CYCLICITY A repeated sequence of beds or rock GRAPTOLITEextinctAn fossil plankton units comprising an elongate tubular structure DEBRIS FLOW A depositional mechanism akin to GRAVEL An unconsolidated accumulation of a mud slide rounded grains of average grain size greater than 4 mm DIP Theangle of inclination of asurface (e.g. BEDDING) in relation to the horizontal GONIATITEA fossil mollusc witha shell of spiral form DISHARMONIC Relating to folds which differ in form with respect to one another GROUNDWATER Water contained in the soil or rock below the water-table DISTAL Distant from HARDNESSpropertyA of water causing DRIFTgeneralA term for all superficial formation of an insoluble residue unconsolidated rock debris ofQuaternary age distinguished from solid bedrock HORIZONTALSECTION interpretive An diagram displaying thestructure and sequence of DRY DENSITY The mass of SOIL afterdrying strata at depth (i.e. solids only), dividedby its total volume before drying HORSTsequenceA of strata betweentwo FAULTS, which is raised relative to adjacent FACIES CHANGEAchange inthe internal strata characteristics of a rock unit IGNEOUS Rock which was originally molten FAULT A surface or zone of rock fracture along whichdisplacement has occurred; movementmay KARSTICRelating to irregulartopography of a either bevertical (normal or reversed), lateral limestone surface by its dissolution (strike-slip) or a combination of the two KETTLE HOLEA steep-sided depression in FELDSPATHIC A depositthat contains the glacial deposits, usually containing clays and peat mineral feldspar in significant quantity laid down in a lake or swamp FIELD-SLIP The base mapon which geological LACUSTRINE Pertaining to a lake observations and comments are recorded LAMINATED A very fine type of BEDDING less FIRECLAY A SEATEARTH comprising quartzose than 1 mm thick clay, capableandwithstanding of high LIMESTONEsedimentary A rockmainly temperature without deforming comprising calcium carbonate FORAMINIFERAMarine protozoan animals LIQUID LIMIT The moisture content at the point (microfossils) between the liquid and the plastic state of a clay FORMATION fundamentalThe unit of LITHOLOGICAL Pertaining to rocks subdivision of a rock sequence which is unified in internal characteristics and differs with respect to LITHOSTRATIGRAPHICALPertaining to the adjacent formations classification 'of rocks onthe basisof their physical characters GEOTECHNICALThe application of scientific methods andengineering principles to the MATURE (of SANDSTONE) Pertaining to a acquisition,interpretation, and useof knowledge predominanceof well roundedand spherical of materials of the Earth's crust to the solution of grains civil engineering problems MAXIMUMSAFE BEARING PRESSURE The GRABENAsequence of strata betweentwo maximum value of contact pressure to which the FAULTS, which is loweredrelative to adjacent soil can be subjected without risk of shear failure; strata it is based solely on soil strengthbut takes into account a suitable factor of safety (usually 3) GRAINSTONE A LIMESTONE where the individual grains of carbonatearedirectin MEMBER A distinctiveunit of stratawithin a contact(grain-supported) fine-grainedand FORMATION carbonate mud is minimal 96 Deeside(North Wales) Thematic Geological Mapping

METAMORPHICPertaining to rocks which have PLASTIC LIMITThe water content at the lower been affected by high temperature and or pressure limit of the plastic state of a clay; it is the resulting in changes in their mineral constituents minimumwater content at which a soil can be rolled intoa thread 3 indiameter without MOISTURE CONTENTThe amount of moisture mm ina given soil mass, expressed as the massof crumbling water in a soil divided by the mass of solids in a PLASTICITY INDEX The difference between the soil watercontents of a clay at the liquid and at the plastic limits. It shows therange of water MUDSTONE A sedimentary rock comprising very fine-grained particles contents for which the clay is plastic PORE PRESSURE The stress transmitted through NODULE(phosphatic, ironstone, carbonate) A small body of mineral or mineral aggregate, often the fluid that fills the voids between particles of a soil or rock mass rounded or ellipsoidal in profile POROSITY The property of a rock, soil or other ONCOLITIC A small concentrically LAMINATED material of containinginterstices; it is commonly CALCAREOUS sedimentarystructure formed by algal growth expressed as apercentage of thebulk volume of materialoccupied by interstices,whether isolated OVERCONSOLIDATED Clay thatstill retains or connected some of theimposed stress from a previous greater overburden PLATFORM (as incarbonate) Pertaining to a very gently sloping sea bed, with little topography PACKSTONE A LIMESTONE which is generally PORCELLANOUSPertaining to a very grain-supported (see GRAINSTONE) butwith fine-grainedcalcareous sediment resembling significant fine-grained carbonate mud matrix, in unglazed porcelain some instancesresulting inseparation of the carbonate grains PRECONSOLIDATION PRESSURE The pressure whichmust be appliedsample ato ain PALAEONTOLOGICALPertaining to thestudy consolidationtest to equalthe maximum of fossil plants and animals overburden pressure to which the sample has been PARTICLE SIZE DISTRIBUTION The percentage subjected in situ of particlesin each size fraction of a sample of PROGLACIALThe environment infront of a soil, sedimentor rock; theresult of particle size analyses glacial ice sheet PROGRADINGRelating to sedimentslaid down PELLOID(PELOID) grainformed A of adeposit which builds outin front of the fine-grained CALCAREOUS materialirrespective as source of the sediments of size or origin PSEUDOBRECCIATED Pertaining to a texture in PERIGLACIAL Said of the process occurring in limestone resembling afragmental rock, but is the region adjacent to glaciers and ice sheets produced by alteration of the limestone PERITIDALA sedimentary environment within QUARTZITICdepositA mainly comprising or near to the tidal range quartz PERMEABILITY Theproperty or capacity of a QUARTZOSE A deposit containing quartz rock, sediment or soil for transmitting a fluid ROCK(Engineering) A naturally found material pHThe measure of the acidity or alkalinity of a withuniaxiala compressive strength over a solution certainminimum value (usually taken as PIPE cavity,A usually in calcareous rocks, IMNme2), and composed of mineral grains commonly filled with clay, sand or gravel ROCKQUALITY DESIGNATION (R.Q.D.) A PIPING Water flow in non-cohesive SAND measure of core recovery incorporating only those causing erosion and formation of channelswithin pieces of found core 100 mm in length; indicative the deposit of thedegree of fracturing;separate values are usually determined for each core run Deeside (North Wales) Thematic Geological Mapping 97

ROC KHE AD The interface betweeninterfaceROCKHEAD The STANDARDPENETRATION TEST An insitu unconsolidated SUPERFICIALDEPOSITS and test for SOIL where the number of blows with a BEDROCK (and usually taken as the baseof the standard weight fallingthrough standard a weathering profile of the bedrock) distance to drive a standard core or sample tube is counted; it is measurea of the BEARING RUNNING Mass flow of non-cohesive SAND due to high water content CAPACITY of a soil STRATIGRAPHICPertaining to thestudy and SAND(ST0NE)sediment (consolidated)A classification of the sequence of rock strata in the comprisinggrains between 0.063 and 4 mm in Earth’s crust average size STRIKEThe orientation of horizontala line SEATEARTHAunit, generally of clay, that drawn on an inclined surface (e.g. BEDDING) underliesa coal andrepresents the fossil soil on which the vegetation grew STYLOLITES Irregularsurfaces within limestone dueto dissolution, andwith insoluble residue SHALE A MUDSTONE withbedding-parallel fissility preserved along the contact SUBARTESIAN Said of confined GROUNDWATER SHEETSAND A unit of SANDSTONE of wide that is under sufficient pressure to rise above the areal extent and limited thickness variation water-table, but not to the land surface SHEAR BOX TEST (DRAINEDAND SULPHATECONTENT Theamount of sulphate UNDRAINED) A test used to determine the shear in groundwater or soil; this gives an indication of strength and residual shear strength of a SOIL the susceptibilitythe of engineeringmaterials, SILT(ST0NE)sediment A (consolidated) particularly concrete and steel, to chemical attack comprising grains between 0.063 and 0.004 mm in SUPERFICIAL DEPOSITS Unconsolidated glacial average size and postglacial sediments SKELETALCarbonate fragments of organic origin SWALLOW HOLES Closed depressions or dolines into which all orpart of astream disappears SLUMPEDPertaining to sedimentdisrupted on underground the sea floor due to gravitational collapse TECTONIC Pertaining to forces which deform or SOIL (Engineering) All materialformed from disrupt strata aggregates of rock particles which can be TRACE FOSSIL sedimentary A structure separated by gentle mechanical means and excavated without blasting comprisingthe fossilised burrow ortrack of a marine organism SOLID BEDROCK geology (excluding DRIFT TRANSMISSIBILITY In an AQUIFER, the rate of deposits) flow of waterthrough each vertical strip of the SOLIFLUCTIONA process involving the slow aquifer having aheight equal to thethickness of downslope movement of superficialmaterial as a the aquifer and under a unit hydraulic gradient result of the alternate freezing and thawing of the TRIAX IAL TEST (DRAINEDTRIAXIALANDTEST contained water UNDRAINED)A test of theshear strength of a SPECIFIC CAPACITY The ratio of discharge of a SOIL sample containedin a rubber membrane water well or borehole per unit of drawdown surrounded by liquid under pressure SPECIFIC GRAVITYThe ratio of theaverage TURBIDITY CURRENT Aturbulent mixture of density of themineral grains that make up a soil sedimentand water which flows on the sea floor to the density of an equal volume of water under the influence of gravity STANDARD The fair copy of the geological map UNCONFORMITYA break in the sedimentary (scale 1:lO 000 or 10 560) sequence with strata of a particular age absent and possibly an angular relationship between the strata of different ages VEIN A mineral infilling of a fault or fracture in a rock, and usually sheet-like 98 Deeside (NorthWales) Thematic Geological Mapping

VERTICAL SECTION A diagrammatic representation of vertical variations in a sequence of strata WACKESTONE A LIMESTONE wherethe fine-grained carbonate mud matrix is predominant andindividual carbonat6 grains (which must comprise more than 10% of the rock) are rarely in contactwith one another (i.e. thegrains are matrix-supported) WELL SORTED Pertaining to a sedimentary rock comprising particles all approximately of the same size ZONALPertaining tosubdivision a (zone) of strata based on its fossil content Deeside (North Wales) Thematic Geological Mapping 99

APPENDIX A: List of British Geological Survey GeosciencesData Centre, British Geological open file reports, 1:lO OOO/lO 560 geological Survey, Keyworth). maps and palaeontological reports produced as SJ 16 byD. Wilson. 1985 (E of gridline%7, part of the project SE at 1:lO 560 scale) Open file reports. (Copies of these reports can be SJ26 SW byJ.R. Daviesand D.Wilson. 1985 purchased either from the Aberystwyth Office of (at 1: 10 000 scale) the British Geological Survey or from the National GeosciencesData Centre, British Geological SJ26 SE byJ.R. Davies and B. Hains. 1985 (at Survey, Keyworth). 1:lO 000 scale) Geologicalnotes and local details for 1:lO 560 SJ36 SW by J.R. Daviesand B. Hains. 1986 (at sheet SJ16 SE (E of gridline 317),by D. Wilson. 1: 10 000 scale) 1986. SI 16 NE by S.D.G. Campbelland D. Wilson. Geologicalnotes and local details for 1:lO 000 1986-1987 (E of gridline 317, at 1:lO 560 scale) sheet SJ26 SW, by J.R. Davies and D.Wilson. SJ 26 NW byS.D.G. Campbell. 1986 (at 1:lO 000 1986. scale) 000 Geologicalnotes and local details for 1:lO SJ 26 NE by B.A. Hains. 1986-1987 (at 1:lO 000 sheet SJ26 SE, by J.R. Davies and B.A.' Hains. scale) 1986. SJ36 NW by B.A. Hains. 1986 (at 1:lO 000 Geologicalnotes and local details for 1:lO 000 scale) sheet SJ36 SW, by J.R. Davies and B.A. Hains. 1986. SJ 17 NE byJ.R. Daviesand S.D.G. Campbell. 1987 (E of gridline 31 7 and S of gridline 378, at Geologicalnotes and local detailsfor 1:lO 560 1:lO 560 scale) sheet SJ16 NE (E of gridline 317),by S.D.G. Campbelland D. Wilson.1987. SJ 17 SE byS.D.G. Campbell. 1987 (E of gridline 31 7, at I:10 560 scale) Geological notesand focal detailsfor 1:lO 000 sheet SJ 26 I NW, by S.D.G. Campbell. 1987. SJ 27 NW by B.A. Hains. 1987 (at 1:lO 000 scale) Geological notesand local details for 1:lO 000 sheet SJ 26 NE,by B.A. Hains. 1987. SJ27 SW by B.A. Hainsand S.D.G. Campbell. 1987 (at 1:lO 000 scale) Geological notesand local detailsfor 1: 10 000 sheet SJ 36 NW, by B.A. Hains. 1987. SJ 27 SE by B.A. Hains. 1987 (at 1:lO 000 scale) Geological notesand local details for 1:lO 560 SJ 37 SW byB.A. Hains. 1987 (at 1:lO 000 scale) sheet SJ17 NE (E of gridline 317 and S of Palaeontologicalreports. (Copies of thesereports gridline 378) by J.R. Daviesand S.D.G. are held on file by theBiostratigraphy Research Campbell. 1988. Group,British Geological Survey, Keyworth to Geologicalnotes and local details for 1:lO 560 whom all enquiries should be addressed). sheet SJ 17SE (E of gridline %7) byS.D.G. Thefaunal biostratigraphy of selectedSilesian Campbell. 1988. localities, N.Wales 1" 96 and 108 for BP West- Geologicalnotes and local detailsfor 1:lO 000 MidlandsSilesian Review. Report PD 85/190 by sheet SJ27 NW, by B.A. Hains. 1988. N. J. Riley. Geologicalnotes and local detailsfor 1:lO 000 Dinantian calcareous microbiota from North Wales sheet SJ27 SW, by B.A. Hainsand S.D.G. (Deeside),Llanarmon andSpring Quarry ? Campbell. 1988. Limestones, 1" 108. Report PD 86/207 byN.J. Riley. Geologicalnotes and local detailsfor 1:lO 000 sheet SJ 27 SE, by B.A. Hains. 1988. Dinantian foraminifera and algae from Deeside N. Wales,1" 108, 121. Report PD 87/336 byN.J. Geologicalnotes and local detailsfor 1:10 000 Riley. sheet SJ37 SW, by B.A. Hains. 1988. Brigantian to Yeadonianammonoid 1:10 OOO/lO 560 geologicalmaps. (Copies of biostratigraphy of variouslocalities, Deeside N. these maps canbe purchased from the National 100 Deeside (North Wales) Thematic Geological Mapping

Wales,1" 108. Report PD 87/380 byN.J. Riley. Namurianfaunal biostratigraphy of two localities in theHolywell Shales (HalkynFormation), Deeside N. Wales,1" 96. ReportPD 87/407 by N.J. Riley. Dinantian calcareous microbiotas from Deeside N. Wales,1" 97, 108,121. Report PD 87/408 byN.J. Riley. . In addition thefollowing files held by the BiostratigraphyResearch Group, BGS, Keyworth andrelevant to thestudy area, were produced at an earlier date. PD/54/20 PD/55/30 . PD/55/26 PD/55/50 PDL68/27 Deeside (North Wales) Thematic Geological Mapping 10X

APPENDIX 8: Geotechnical Tests quoted in the plasticity. Database and their applications Atterberg or Consistency Limits The Standard Penetration Test (S.P.T.) As the moisturecontent of a cohesive soil Thestandard penetration Test (S.P.T.) is a increases it will pass from solida state to a dynamictest carried outat intervalsduring the semi-solid statein which changes inmoisture drilling of a borehole. A standard 50 mm contentcause a change in volume. The moisture diametersplit barrel sampler is driveninto the content at thischange is theshrinkage limit. As soil atthe bottom of the hole for adistance of the moisture content is increased further, the soil 450 mm by the blows of standarda weight will become plastic and capable of being moulded; (65 kg), fallingthrough standarda distance the moisture content when this change takes place (0.76m). Thenumber of blows (N) required to is the plastic limit. drivethe last 300 mmis recorded. [Details are given in B.S. 5930 (BritishStandards Institution Ultimately, as moisturecontent is increased,the 1981)]. soil will become liquidand capable of flowing under its own weight. Thischange takes place at A modification of the test for hard material and a moisture content called the liquid limit. coarse gravel uses a solid cone instead of a cutting shoe andis called conea penetrometer test The plasticity index is defined as the liquid limit (C.P.T.). minus the plastic limit and gives therange of moisture content over which the soil behaves as a Althoughthis is afield test which is subject to plastic material. The methodsand apparatus for operationalerrors, the S.P.T. is widely used to determining the consistency limits are described in give anindication of the relativedensity of B.S. 1377. granular soils (very loose tovery dense) and the consistency of cohesive soils (verysoft to hard). The,factors which control the behaviour of the Correlationshave also been made between S.P.T. soil withregard to consistency arethe nature of and the bearing capacity of a soil. mineralsclaythe present, theirrelative proportions andthe amount and proportions of Rock Quality Designation (R.Q.D.) silt, fine sandand organic material. If plasticity index is plotted against liquid limit on a plasticity Rock quality designation (R.Q.D.)was introduced diagram,a soil may beclassified in terms of its by Deere (1964) to give anindication of rock plastic behaviour. The consistency limits also give quality in relationto the degree of fracturing an indication of soil strength and compressibility. fromdrill cores. It is defined as the sum of the coresticks in excess of 100 mm lengthin Density Tests expressed as apercentage of thetotal length of coredrilled. The parameter takes no account of Bulk density is calculated by dividingthe total thedegree of fracture opening orthe fracture massof a soil (solids andwater by its total condition and does notdistinguish between volume. It may be determinedbythe sand fracture spacings of morethan 100 mm.R.Q.D. replacementmethod (in the field)or thecore has been used withuniaxial compressive strength cutter method. Ineach of these a measured to give an indication of excavatibility and as one volume of soil at itsnatural moisture content is input for the classification of rock masses to assist weighed and its density calculated. in thein design of tunnelsupport systems Dry density is calculated by dividing the mass of (Bieniawski, 1974; Barton and others, 1974). soil after drying (that is, solids only) at 15OoC to constant weight, by its total volume before drying. Moisture Content Saturateddensity is calculated by dividingthe Themoisture content of a soil is defined the as mass sf soil with its pore spaces filled with water, mass of waterin a soil divided by the massof by totalits volume. Full- details of the solids ina soil, expressed as a percentage. It is determination of soil density are given in determined by weighing a sample before and after B.S. 1377. The density of soil in its various states drying to constantweight at atemperature of of saturation are basic soil properties which are 105OC [details are givenin B.S. 1377 (British used in a variety of calculationsincluding Standards Institution 1975)l. Moisture content is a assessing overburdenpressure, slope stability, b&ic soil propertyand influences soil behaviour surcharge pressure, andearth pressure on withregard to, for example, compaction and

.. 102 Deeside (North Wales) Thematic Geological Mapping retaining walls. arate controlled by the soil permeability.The removal of water causes a decrease in volume of Triaxial Compression Test the soil; this process is called consolidation. TheTriaxial compression test is the most widely The consolidation parameters are measured in the used test fordetermining the shear strength of laboratoryby placing adisc of soil ina metal cohesive soils and a number of different methods ring,in a water-filled cell. A constant axial load may be used depending on the application of the is applied to the disc and its decrease in thickness results. measuredwith time. When it reaches aconstant thickness fora given load, the load is increased Inthe simplest, mostcommon method (quick (usually doubled)and the readings repeated.The undrained),cylindrical a specimen (usually loading is continueddepending on the soil type 76 mm x 38 mm) is placed between rigid end caps andthe structure for which the data is required. andcovered with rubber a membrane. The Thecoefficient of volumecompressibility, M,, assembly is then placed in a triaxial cell which is can then be calculated. This is ameasure of the filledwith water and all air is removed. The amountof volume decrease that will take place water pressure in the cell is then maintained at a fora given increase in stress. Thecoefficient of prescribedconstant value while the axial load on consolidation, which is ameasure of the rate thespecimem is increasedat a constant rate of C,, at which the volume change will take place for a strain.The test continuesuntil either the given increase in stress, is also calculated. specimen shears ora maximumvertical stress is reached. Verticaldisplacement, axial load and The consolidation test results areimportant for pore pressure within the sample are measured designing thefoundations of structurea and duringthe test. The test is repeatedon two calculating thesettlement that will take place further specimens fromthe samesampling point during and after the construction of a building to butattwo different confining pressures. The ensurethat settlement is neither excessive nor results obtainedfrom the three tests enable the unevenover the foundation. It may also be undrainedshear strength to be calculated as C,, important to ensuresettlementthethat theapparent cohesion, and q5,, the angle of (consolidation) which is caused by an early stage shearing resistance. Theparameters obtained of construction has ceased before a second stage is fromthis test maybe used todetermine the started. immediatebearing capacity offoundations in saturated clay. Permeability Other variations on the test are suited to different The permeability of a soil is its capacity to allow applications. Inthe consolidated undrained test, water to flowthrough it. It maybe measured in freedrainage of thespecimen isallowed under the laboratoryon samples or in the field using cell pressure for 24 hoursbefore testing (that is, boreholes. the samplethe consolidates). Drainage is then In thelaboratory, two tests are commonly prevented and the test carried out before. This as employed,constantthe head test for test is applicable to situationswhere sudden a coarse-grained soils andthe falling head test for change in load takes place after a period of stable fine-grained soils. In theconstant head test a conditions, for example where rapid drawdown of sample of granular soil is confinedin a perspex the water behind a dam takes place. tube,a constant head of water is applied to one In thedrained triaxial test, freedrainage is endand water is allowed to flowthrough the allowed duringthe consolidation phaseand also sample. Manometers areconnected through the duringthe test itself. The results obtainedwould cylinder wallsto monitorthe pressure along the be applicablelong-termto slope stability flow path. Permeability may then be calculated, assessment. using Darcy’s Law, from the path length, pressure difference, cross-sectional area of the sample and Consolidation Test the quantity of water passed in a given time. If asaturated cohesive soil is subjected to an In a falling head test a sample of fine-grained soil increase in loading, the pressure of the waterin containing clay or silt is placed in acylinder the pore spaces will increase by the same amount standingin a tray of water,a glass standpipe is as the applied stress. The water will therefore connected to the top of the sample and filled with tend to flow away to areas at a lower pressure at water. Thetime taken for the water level in the Deeside (North Wales) Thematic Geological Mapping I03 standpipe to drop a given distance is then a volume of 500 ml. It is then agitated vigorously measured. Permeability may then be calculated and allowed to settle. Samples are removed by fromthe time,the dropin height, the pipette from a given depth at specific times. The cross-sectional area of standpipe,the the samples aredried and thecontained solids cross-sectional area of the sample andthe length weighed. The size distributioncan then be of the sample. (Details are given in B.S. 1377). calculated using Stokes’ Law which relates settling Laboratory tests donot take into account the time to particle size. The entirg grading curve for structural differences in the soil and may not give coarse and fine material can then be plotted. Full details are given in B.S. 1377. a true permeability of the ground en masse. Pumping tests using boreholes give more a Particle size distribution is used for classifying representative value but are more expensive. soil in engineering terms (B.S. 5930). Particle size In afield permeability test water is pumped out distributioncurves will indicate soil behaviour with regard to permeability, susceptibility to frost of a borehole and the effect on the water level in heave or liquefaction,and will give some adjacent boreholes is monitored; if singlea borehole is being used it may be pumped out and indication of strengthproperties. Particle size analysis does not,however, indicate structure and the water level recoverytime recorded. An alternativeapproach is to pumpwater into a will notdistinguish between a sandy clay anda laminatedsand and clay which may behave very borehole under pressure and measure the volumes differently. of water flowing into the borehole at a number of different pressures(details are given B.S. 5930). Theinformation obtained from either method Compaction enables coefficienta of permeability for the Thecompaction test determinesthe moisture ground as a whole to be calculated. content(the ‘optimum’) at which a soil may be Permeabilityis used topredict the inflow of compactedmaximumitsto dry density. A water duringexcavation ortunnelling and to quantity of soil (5 kg) is compacted in a standard mould using astandard rammer (2.5 or 4.5 kg) design groundwatercontrol schemes todeal with which is droppedfromstandard a height it. Permeability is important when assessing waste (300 mm or 450 mm) a standard number of times disposal sites or thesiting and construction of (27). The density of thecompacted soil is then water-retainingstructures such dams, lagoons as measured andits moisture content determined. and canals. The assessment of potential well yields requiresfield permeability determination Theprocedure is thenrepeated using the same soil at different moisture contents. for the formations concerned. Thedry density of thecompacted soil is plotted Particle Size Analysis againstitsmoisture content and themoisture contentat which maximum compacteddensity Theparticle size distribution of a soil is may be achieved is read fromthe curve. (Details determined by sieving and sedimentation. A are given in B.S. 1377) sample of soil is dried, weighed andsieved to remove thefraction greater than 20mm in size. The results of the compaction test show the It is thenimmersed in water with a dispersing moisturecontent at whichit is best to place a agent such as sodium hexametaphosphate to break given soil as fill or in an embankment. up soil aggregates. The sample is then wet sieved to remove particles less than 63 pm. The fraction California Bearing Ratio (C.B.R.) retainedon the63 pm sieve is driedand passed The California Bearing Ratio test is a penetration througha nest of sieves ofmesh size ranging test carried out in the field, or in the laboratory, from 20mm to 63 pm. Thefraction retained on which comparesthe resistance of a soil to each sieve is weighed andthecumulative penetration by a standard plunger to the resistance percentage passing each sieve is calculated. A to penetration shown by a standard crushed stone. gradingcurve of percentage passing against sieve size is plotted. A series of samples arecompacted in a 152mm diameter mould atmoisture contents around the Thefines which passed through the 63 sieve pm optimummoisture content for maximum aregraded by sedimentation. A representative compaction. A surcharge weight is placed on the subsample is made up intoa suspension with soil which is then immersed inwater forfour distilled water, placed in a tall jar and made up to days. The mould is placed ina load frame anda

.- 104 Deeside (North Wales) Thematic Geological Mapping

plunger 48.5 mm indiameter is forced into the Specific Gravity sample to apenetration of 2.5 and 5 mm. The The specific gravity of a soil is the mass of a dry C.B.R. value is determined as thehigher of the soil divided by the massof waterdisplaced by ratios of theresistance at 2.5 mm and 5 mm that soil and is, therefore,dimensionless. For penetrationto the standard resistance of crushed fine-grained soils, a 50 ml density bottle is used, stoneat the samepenetrations. (Details are given whilst forcoarse-grained soils, a 500 or 1000 ml F in B.S. 1377). Inthe field, the plunger is jacked pycnometershould be used. Fulldetails of the intothe ground against the reaction of aheavy test are given in B.S. 1377. lorry.(Field values areusually lower than laboratory values). Theresults of the C.B.R. test Specificgravity is basica soil propertyand are used to assess the suitability of soils for use as represents an average for the particles of different base, sub-basesub-gradeand in road mineralspresent in the soil. Theparameter is construction. used toenable calculation of otheruseful soil properties.For example, voids ratio (which is Chemical Tests related to porosity)can be calculatedfor a saturated soil if the moisture content and specific pH About 30 g of soil are weighed and placed in gravity are known. 75ml of distilled water in a beaker. The mixture . is stirredand allowed to infuseovernight. A glass electrode connected to a pH meter is then placed inthe stirred mixture and the pH readingtaken. Theelectrode and meter mayalso be used to determinethe pH of groundwater samples; pH mayalso be determinedcolorimetrically. Details are given in 3.S. 1377. The pH of soil or groundwater is important when designingconcrete structures below ground surface.Ordinary Portland cement is not recommendedin situations with a pH below 6, highalumina cement can be used down topH 4 andsupersulphated cement has been used to pH 3.5. Acidic groundwaters can also cause corrosion in buried iron pipes. Sulphate Thesulphate content of soil is determined by leachinga weighed sample of soil withhydrochloric acid and precipitating the dissolved sulphate by the addition of an excess of bariumchloride. The precipitate is thenfiltered, ignited in a furnace and weighed. Thesulphate content of groundwateroran aqueoussoil extract is determined by passing the waterthrough acolumn of ionexchange resin whichconverts sulphatethe content to hydrochloricacid. The acid content, and hence sulphate, is thendetermined by titrationwith sodium hydroxide. Details are given in B.S. 1377. It is importantto know thesulphate content of groundwaterand soil because ordinaryPortland cementdeteriorates in the presence of suiphate. Knowledge of thesulphate concentration present enables a suitablesulphate-resisting or high alumina cement to be used in appropriate concrete mixes for applications below ground level. Deeside (North Wales) Thematic Geological Mapping 105

APPENDIX C List of boreholes

.. BGS Grid Date of Surface Drift ’ Engi neeri ng Number Reference drilling, -7 eve1 thickness Depth properties MAP SJ 16 NE 1 18956613 244.75 60.96 - 2 19106625 239.26 60.96 - 3 19096610 234 -08 60.96 - 4 19176610 225.24 60.96 - 5 19226625 232.56 60.96 - 6 18226802 1964 20.11 51.81 - 8 17036964 1978 145 .OO 11.70 11.70 - 10 17326868 II 182 .00 8.30 8.30 - 11 17546780 11 159 -00 7.30 7.40 - 13 17506697 1979 184. 00 18.00 18.00 - 14 18366854 1978 204 .OO 3.60 3.80 - 15 18326776 II 153.00 4.00 4.00 - 16 17966674 1979 187 .OO 10.50 14.00 - 17 18476526 I1 179.00 18 .00 18.00 - 18 19536681 1978 169 .OO 7.50 13.70 - 23 c 183 677 150 .00 9.30 9.30 -

MAP SJ 16 SE 1 17206466 1978 215 .OO 3.50 3.50 - 2 19116222 1979 209 .00 4.40 4.40 - 3 18876302 1978 206.00 6.50 6.70 - 4 19196200 II 208.00 4.20 4.30 - 5 19116113 II 202 000 4.80 4.80 - 6 1888 6G48 1979 213.00 3.50 3.50 - 7 19566341 II 228 .OO 2.10 2.20 - 10 18876066 1952 1.68 1.68 - 11 18906057 I1 1.52 1.52 - 12 18866048 II 1.22 1.22 - 13 18836038 II 1.22 1.22 - 14 18916036 II 1.98 1.98 - 15 1825 6135 1967 268.53 2.44 2.44 - 16 18506149 II 249.14 1.98 1.98 - 17 1871 6162 11 228.72 2.44 2.44 - 18 18906179 It 218.97 2.44 2.44 - 19 19066201 II 213 .36 2.59 2.59 - 20 19216197 II 208.06 2.44 2.44 - 21 19456221 201 047 1.83 1.83 - 22 1972 6247 183.61 2.44 2.44 - 23 19926258 186.20 2.74 2.74 - 24 19836273 179.34 5 079 5.79 - 25 19796231 194.01 1.83 2.44 - 26 1976 6217 216.68 1.37 1.37 - 27 19756195 228 078 1.37 1.83 - 28 19586158 228 .39 0.23 1.22 --- 29 19566134 232.47 0.23 1.83 - I06 Deeside (North Wales) Thematic Geological Mapping

BGS Grid Date of Surface Dri ft Engi neeri ng Number Reference drilling 1eve1 thi ckness Depth properties

30 1975 61101975 30 1967 241.74 2.13 2.13 9

MAP SJ 17 NE

1 19497757 1917-8 15.24 21033 363.93 2 c 19437751 1921 c 12.19 18.28 177.69 3 c 19537749 1921 c 12.19 20.11 77.11 4 c 19497747 1933 12.19 c 15.60 243.84 5A c 19737768 1942 15.54 15.54 5B c 19737768 1945 c 6.09 17.37 17 037 6 18467613 c 1890 c 89.91 23.77 30 .63 16 17007535 1973 230 .00 2.00 15 .lo 17 17097534 II 228.70 3.30 15.30 18 17287524 II c 7.00 29 .96 19 17427527 I1 c 2.00 20 .00 20 17557520 I1 c 6.00 19 .54 21 17667514 I1 227 .OO 6.00 15.05 22 17717511 II c 4.00 18.50 23 17827507 11 c 12.00 28.80 24 17927501 II 224.50 3 045 3 045 25 17887503 I1 224.50 6.45 6.45 26 17847505 II 225 .OO 8.00 8 000 27 17777505 II 224 .50 6.45 6 -45 28 17757509 I1 225 .00 4.00 4 .OO 29 17567517 I1 228.50 5 000 5 000 30 17477521 u 230.00 5 080 5.80 31 17457518 II c 6.00 22.00 32 17377523 I1 229 .50 2.85 2.85 33 17287529 11 229 .00 3 .OO 3.00 34 17187530 I1 228 .50 3.60 6.15 65 . ? 194774 c 91.00 24.06 30.48 67 19957649 1986 c 56.00 4.00 5.00 68 19907685 1973 37 .25 2 000 2 000 69 '19977717 I1 6.70 5.00 5 000 70 19957713 I1 12.00 7 000 7 000 71 19907708 I1 19 -25 3.00 3 000 72 19807707 II 21 055 3 .OO 3 000 73 19807698 II 22.65 3.00 3 .OO 74 19767772 I1 5.50 3 000 3.00 7511 18987537 1975 114.58 10.50 10.50 7512 18967541 I1 102.51 10 .50 10.50 7513 19007539 I1 109 -95 10 .50 10 -50 7514 19047536 I1 108.75 10 000 10. 00 7515 19077535 I1 108.60 10 000 10 000 7516 19117534 I1 108.32 10.30 10.30 7517 19167536 11 106.78 11.00 11 000 7518 19137538 II 105.48 10.65 10 .65 7519 1909 7539 I1 105.51 28.50 28.50 75/10 19067540 11 105.99 11 000 11 000 75/11 1903 7545 I1 103.93 15.50 15.50 75/12 19077544 I1 104.88 11 000 11.00 75/13 19117543 II 104.40 12.60 12.60 75/14 19147541 I1 103.89 15.50 15.50 75/15 19187539 It 104 .12 10 .00 10 000 Deeside (North Wales) Thematic Geological Mapping 107

BGS Gri d Date of Surface Dri ft Engineering Number Reference drilling -1 eve1 thickness Depth properties * 75/16 19187545 1975 100 053 22 050 22.50 Yes 751 17 19167545 It 101.81 15.50 15.50 I1 75/18 1913 7547 I1 103.82 15.70 15.70 11 75/19 19107549 I1 101.95 10.50 10 .50 I1 75/20 1911 7552 I1 101. 47 10.00 10 000 11 75/21 19147550 I1 103. 66 17 .OO 17.00 11 75/22 19187547 I1 100 .54 15.50 15.50 I1 75/23 19227546 I1 97.60 15.60 15.60 II 75/24 19207551 11 99.14 15.60 15.60 II 75/25 19167553 If 101 019 20 000 20 .00 I1 75/26 19127555 I1 101.51 15.50 15.50 I1 7 5/ 27 1900 7556 I1 103.49 15.50 15.50 I1 75/28 18967557 I1 104.74 10.05 10.05 11 75/29 18957553 II 108 .29 10.66 10.66 I1 75/30 18997553 I1 108.54 15.50 15.50 I1 75/31 19037555 I1 103.64 10 000 10 000 I1 75/32 1903 7552 II 103.64 10 000 10 000 It 75/33 19027548 I1 105.38 11 000 11 000 11 75134 18957548 11 111.28 10 000 10 000 II 75/35 1891 7549 I1 110.82 11 000 11 000 11 751 36 18917553 I1 109.65 10.00 10 000 11 76 18947546 1973 110 .85 8.00 8 .OO I1 77 18927549 II 110 090 15 .OO 15 .OO II 78 18907552 I1 109.70 10 .oo 10 000 11 79 18957549 I1 111 20 14.50 14.50 II 80 18717602 1974 100.50 15.50 15.50 11 81 18747599 I1 101000 15 .OO 15.00 II 82 18717598 I1 101.50 15-00 15 .OO 11 83 18757599 11 102 075 15.OO 15.OO II 84 18687597 I1 102.80 15 .OO 15 -00 11 85 18717593 11 103.10 15.00 15 .OO 11 86 18747596 I1 102.40 15 .OO 15 .OO 11 87 18547588 1984 109 .48 10 .oo 10 000 II I1 11 - 88 1850 7585 114.14 10 .oo 10 .00 89 18547577 I1 116 -05 10 000 10.00 11 90 18597582 I1 111.76 10 000 10 000 11 91 18477570 I1 124 .10 7 -90 10.00 11 92 18497568 I1 121.88 10 000 10 000 11 93 18597569 I1 117.95 10.00 10.00 II 94 19507754 I1 14.40 9.00 9 000 II 95 19517755 I1 11.87 8 .OO 8.00 11 96 1895 7670 1973 45 .20 5 -40 5.40 97 19077698 11 39 000 5.20 5 20 98 19257719 I1 36.30 25 .OO 25 .OO 99 19197707 It 35.90 10.00 10.00 100 1949 7745 I1 20.80 10 000 10 .oo 101 19297720 11 31.50 10.00 10.00 102 1887 7647 I1 93 .OO 3L50 31.50 103 1884 7.680 I1 70.30 25 .OO 25.00 104 18687610 11 100.50 15 .50 15.50 105 1868 7604 I1 91.70 11 *oo 11.00 108 Deeside (North Wales) Thematic Geological Mapping

BGS Grid Date of Surface Dri ft Engi neeri ng Number Reference drilling, -1 eve1 t hi ckness Depth properties MAP SJ 17 SE

2 19447287 ? 1961 7.31 83.82 3-20 C.E.G.B. - Confidential 21 18187485 1973 218.50 22.80 26 .OO Yes 22 18227482 I1 218 .OO 32 .70 32 .70 i1 23 19337429 It 195.50 3.55 9.62 It 24 19337427 I1 196.50 5.20 10 000 It 25 19367418 I1 200 .00 1.90 5.56 i1 26 19497417 I1 184. 50 6.50 10.93 11 27 19667400 I1 179 .So ?4.40 17.50 11 28 19997346 I1 183 .00 6.45 6 -45 11 29 19977352 I1 183.40 8.20 8.20 11 30 19907363 I1 182 .OO 8.00 8 .OO If 31 19887369 I1 179 a50 5 045 5.45 11 32 19817381 I1 180 .OO 4 a00 4 000 11 33 19787382 I1 178.50 4.25 10.40 11 34 19797387 I1 176 .OO 4 .OO 4 .OO 11 35 19587379 11 196 .OO 5.40 12.15 II 36 19717388 I1 181.OO 3.90 4.30 11 37 19597387 I1 187.50 1.95 6 22 11 38 19657393 I1 184 .OO 0.65 6.22 11 I1 39 19667399 180 .00 C 3.00 17.50 11 40 19687400 I1 179 .OO c 2.30 11.50 11 41 19687401 I1 178.50 - 6.08 11 42 19657402 I1 179 .OO 0.20 8.22 11 43 19627402 I1 180.50 1.65 8.22 11 . 44 19647410 I1 177.00 7.50 7.50 It 45 19597409 I1 182. 50 1.50 4.85 11 46 19567414 I1 178.50 1.70 4 000 11 47 19397411 11 200 000 1.80 3 000 11 48 19437421 I1 191.50 3.00 3.00 11 49 19317427 I1 196 .OO 9 000 9 000 11 50 .19247432 I1 196 -00 4.75 4.75 11 51 19287441 11 186 .OO 0.30 4 .OO 11 52 19157436 I1 198 .OO 2 000 3.02 11 54 19037439 I1 204.50 3.45 3.45 11 55 18977443 I1 204 .OO 3.00 3 .OO 11 56 18897445 I1 217.50 9.45 9 045 II 57 18807449 11 219.30 ?2 000 4.57 11 58 18787447 I1 220 000 2.75 2.75 11 60 18697451 11 225 .OO 11.45 11.45 11 61 18607455 It 227 .OO 20.63 20.63 11 62 18517462 I1 224.00 9 045 9 045 11 63 18437468 I1 224.00 4 .OO 4 000 11 64 18347474 11 220 000 5 .OO 5 000 II 65 1826747% I1 215.00 10.00 10.00 66 18207481 I1 219.50 6.00 6.00 67 18227487 I1 218 .OO 6 .OO 6 .OO 68 18097492 I1 223 .!io 6.30 6.30 69 18027497 I1 228 .50 2.30 2.30 71 19737393 I1 174.00 3.05 8.07 72 190718 1972 229 .00 63 .OO 73 c 198740 1976-77 27 closelyadjacent boreholes 74A 19137443 1978 189.30 6.40 12.30 Deeside (North Wales) Thematic Geological Mapping 109

BGS Grid Date of Surface Drift Engi neeri ng Number Reference drilling 1 eve1 thickness Depth properties

746 1927 7438 1978 188 e 30 3e00 10 e 20 Yes 74c 1899 7435 II 209 e90 ‘4 e60 14e30 II 11 II 74D 1910 7436 205 e50 3 e50 15 e40 74E 1904 7439 II 205 e80 7e50 7e50 II 74 F 1906 7444 II 191eOO 7.30 7.30 II 746 1913 7436 II 207 e20 7 e20 7 e20 11 74H 1915 7441 II 188.10 4.70 5 e50 II . 11 II 74 I 1921 7433 199 e 70 6 e60 6.60 745 1923 7437 II 191 e40 3.20 3.20 It 74K 1900 7446 I1 194 e00 9.20 12e50 II 74L 1911 7443 II 191 e00 3 e60 6e36 II 74M 1898 7438 II 209 .00 4 e85 9.50 II 74N 1908 7437 1977 206.75 10e30 10 e85 I1 II II 74P 1904 7443 197 e 50 7 e50 10.80 II It 74Q 1918 7438 195 e 25 8e00 18.50 II II 74R 1928 7434 193.50 13-15 22 e 50 74s 1901 7436 II 213 e75 3 e10 9 000 II 79 1862 7446 1978 236 e02 8 e95 14.45 II II II 80 1875 7437 239 e 96 11 e00 20 .oo 81 1890 7427 11 235 e71 16.45 19-65 II II 11 82 1899 7419 239 e84 2 e75 15 e10 83 1904 7408 II 248 e06 2.65 18 e00 II 84 1916 7400 I1 231 e30 4e45 7 e50 II II II 85 1938 7374 219 e 78 5 e85 11 e10 86 1956 7356 II 211 e14 9e00 12 e00 II 87 1951 7350 II 223 e87 8.90 14.40 II 88 1972 7331 II 210 e48 12 e60 16 e00 II 89 1906 7410 II 237 e68 7 e65 9.70 II 103 1778 7453 1986 c 226.00 3.90 3 e90 II 104 1706 7105 1972 le00 1 e00 II 105 1704 7109 II 1 e80 1 e80 II 106 1702 7106 II le50 .le50 II I1 H 107 1704 7107 1 e50 1 e50 108 .1787 7417 II 2 .oo 2 e00 II 109 1782 7422 I1 2.50 2 e50 It . 110 1786 7425 11 1 e50 1 e50 II 111 1790 7428 11 2 e00 2 e00 II II II 112 1786 7431 2 e50 2e50 113 1794 7426 II 1 e00 1 e00 II 114 1791 7423 II 1 020 1 e20 II 115 1794 7416 II 3eOO 3 e00 II 120 1895 7070 II 3.50 3e50 II 121 1896 7073 11 2.40 2.40 II 122 1898 7073 II 2.50 2.50 II 123 1897 7076 II 2.25 2.25 II

MAP SJ 26 NW

1 2090 6598 c 1949 119 e 78 13.41 13e41 5 65022316 ? 1947 5e33 30 e48 6 65022318 1948 ? 35.36 7 65012319 II ? 35 e36 8 67102054 1979 122 e00 4.10 4e10 9 68482086 II 231 e00 7e20 7.70 110 Deeside (North Wales) Thematic Geological Mapping

BGS Gri d ~ Date of Surface Dri ft Engi neeri ng Number Reference drilling 1eve1 thickness Depth properties 10 197967602118 208 .OO 20.30 20.30 - 11 21376704 11 174 .OO 25 a50 25 30 - 12 21156623 11 145 -00 7 a40 7.50 - 13 21206505 I1 164 a00 13 a80 14. 00 - 11 14 22376782 202 a00 9 a00 9 a00 I 11 15 2215 6671 178.00 6 .OO 11 000 0 16 197868722365 122.00 5 a20 6 .OO I 17 197967172350 151.OO 7 a90 7 a90 - 11 18 23296664 133.00 14.20 14.20 0 I1 19 22966565 160.00 25 a00 25 a 00 - I1 20 22906519 108 .OO 11 a40 11 a50 .I 21 197869392428 90 000 21 a60 21a60 - 22 197967442430 123-00 26 a00 26 .OO - I1 23 24046526 146 a 00 14.70 15 .OO 0 24 PSA - Confidential 25 198169902292 113.11 5 000 5 a00 Yes 26 23166981 11 97 a25 11 a50 12 a14 I1 27 23176977 I! 96 a08 6 a50 6 a80 I1 I1 28 23216981 . I' 81a22 13.00 13 a00 29 23206976 I1 84.75 ?16a20 16.50 I1 30 23226977 11 82.61 14 a00 14 a00 I1 31 23356974 I1 104 a49 5 a20 5 a20 I1 32 23376975 I1 103.99 5 .OO 5 .OO I1 33 23456977 II 103.40 6 a00 6 a00 I1 34 23626962 I1 97.85 5 a05 5 a05 If 35 23976940 11 98 a22 6 .OO 6 a00 I1 36 24146927 I1 96.09 5 a00 5 a00 II 37 2427 6913 I1 99.14 7.00 7 .OO I1 38 24326919 I1 96.02 5 a00 5 a00 11 39 24246906 II 102 a64 ?9a70 9a70 I1 I1 11 40 24486909 89 a 88 7 a50 7a50 41 24626895 II 90 a97 5 a00 5 000 I1 42 24826885 I1 90.71 5.50 5.50 I1 43 .24456904 I1 93.25 7.50 7.50 I1 44 24476903 11 93 035 30 a00 30 a00 II 45 24486899 I1 94.36 30 a00 30aOO I1 11 46 24466899 95 a56 8.50 8.50 II , 47-76 British Coal - Confidential - a7 24806594 19.20 39 .20 Yes 88 24896598 23 a00 41a76 It 89 24936598 26.50 43 a00 11 90 24936856 2 a00 2 a00 11

MAP SJ 26 NE 3A 69212992 1961 11 a73 3 a07 3.07 I1 - 3B 69372968 16-15 4.26 4 a26 3c 69452943 I1 19.41 2a74 2a74 3D 69482909 It 27.96 2 a89 5.18 3E 69612888 I1 26.27 3.04 3 014 3F 69782942 I1 19.12 3.96 5 a18 3G 68882991 11 16.30 3 a04 3 -04 4 66752683 1861 c 112.77 22 a86 196.90 6 66742599 1878-9 c 122.83 3.04 101.49 Deeside (North Wales) Thematic Geological Mapping I I I . BGS Gri d Date of Su rf ace Dri ft Number Reference drilling -1 eve1 thi ckness Depth 10 2996 6671 1960 81.56 6 -10 6 .lo 11 2796 6598 1967 2.13 41.65 12 2797 6573 II 0.60 18 .28 13 28046577 I1 2.05 29 .36 14 2812 6578 II 2.13 6.52 15 28016559 14 2.13 32.31 16 2806 6558 II 2.13 36.27 17 25496501 1974 152 .OO 11.80 32.10 18 25546503 I1 152.00 8 .lo 34 .lo 19 25696513 I1 148.50 8.90 34 .60 20 2586 6541 I1 140 .OO 9.20 30 .40 21 29146703 1972 78.68 10 000 12.20 22 27986667 I1 92.58 7.10 9 a00 23 2866 6605 II 108.80 1a00 15.20 24 29286630 II 85 .76 8 -90 12 010 25 29426515 II 117.97 2.40 16 .OO 26 25596852 1979 102 a00 17 .lo 17 .lo 27 26316764 ll 89 .OO 13.10 13.60 28 2706 6589 II 115 .OO 6.80 9.00 29 28236871 II 74 .oo 9.50 10 10 30 27956753 II 84.00 14 .lo 14 .50 31 2825 6646 II 91 000 14.80 15.30 32 2915 6701 II 82 .OO 11.90 12 010 33 2650 6865 I1 98 .00 6.30 6.40 34 27516910 II 79 .00 4.30 5 .20 35 28356771 II 89.00 19.40 19 .40 36 25026869 1981 92.07 10a00 10 000 37 25016867 II 91.40 10 000 10.00 38 25286830 II 99.84 5 *oo 5 a00 39 25296828 I1 100.89 8.00 8 .OO 40 25346823 II 101a20 12 020 12.30 41 25356821 II 100.80 12.50 12.70 42 2536 6823 II 100 a45 12.90 13.10 I1 43 - 2540 6815 96 .78 5 000 5 000 44 25496800 II 97.36 5 000 5 -00 45A c 264 679 137.29 45B 187 .65 46-695 British Coal - Confidential 7151983 6938 2991 5.99 4.90 4.90 7 16 29856941 II 4.85 3 020 3.48 717 2975 6949 I1 4.70 3 .BO 4.25 7 18 2970 6947 11 6.06 3 000 4.31 719 29616954 II 5.96 2 000 3.25 720 29486962 II 6.15 1.90 2.50 2551 6502 1972 150.72721 1972 6502 2551 9.81 9.81 722 25636509 I1 151.58 8.30 10 000. 2763 6700 1975 90.50723 1975 6700 2763 8.90 14 .50 7 24 27616699 11 8.90 15.70 725 2761 6697 II 91 a50 5.90 12 a20 726 27486709 11 89.00 10.40 21.30 727 27536706 rI 79 050 - 15 a10 7 28 2757 6702 I1 2.70 40.00 7 29 27656696 I1 91.50 7.40 40 .OO 730 27846680 11 94 .OO 3.80 25 .OO 731 27876678 I1 94 .OO 4.70 17 .OO I12 Deeside (North Wales) Thematic Geological Mapping

BGS Gri d Surface Drift Engineering Number Reference 1 eve1 thickness Depth properties 732 27936672 94 .OO 2.50 15.00 Yes 733 27966668 94 .OO 3.50 35 000 It 734 28166648 92.50 7 000 11.50 It 735 28236641 92 .OO 6.40 17.50 i1 736 28216639 92.00 6.40 15.00 It 737 28236641 92.50 7.70 15.25 It 738 28296630 94.00 2.80 9 000 i1 7 39 28286634 94.00 4.40 30 .OO It 740 28346633 93.50 2.40 12.00 It 741 28296638 92.00 4.40 40 .OO 11 742 28286634 93.00 4.70 9.50 11 743 28396627 3.80 17 .OO 11 744 28436632 744A 2843 6632 1.30 18 .OO Yes 745 2845 6624 95.00 1.90 30 .75 11 746 28486620 96.50 2.30 37 .OO II 747 2857 6619 2.30 20 eo0 II 748 28636617 104 .OO 1.40 20 000 11 749 28646613 106 .OO 0.80 14 .20 11 750 28666619 100.50 1.40 20 000 II 751 2074 6617 95.50 2.70 14 .OO 11 752 28726613 100 000 1.80 14.00 11 753 28706614 2.20 14.10 11 754 28676618 100 000 2.80 9 000 11 755 28686613 103.50 1.50 8.80 It 756 28666613 105 .OO 1.80 14.00 11 757 28746614 99 000 0.90 40 .00 11 758 28776616 95.00 2.90 a .oo It 759 2885 6613 93.00 2.80 10 000 It 760 2895 6606 95 .OO 3.20 18.00 11 761 2896 6616 90 000 4 .OO 12.80 It 762 28976614 89.00 3.20 19.30 11 11 763 . 28976612 3.70 18.60 764 -2898 6610 88.50 4 000 8 -00 11 765 29006611 88 .OO 3.30 9 035 11 766 28996612 88 .OO 3.20 30 .OO 11 767 28996614 88 .OO 3.50 19 000 II 768 28996616 3.20 9 010 11 769 28976625 88 .OO 4.80 20 .oo II . 770 29056614 87 .OO 3.50 25 .OO 11 771 2913 6628 86.50 15 .OO 24 .00 It 772 29156616 86.00 8.50 12.20 11 It 773 29226624 6.90 24 .OO 773A 29366623 774 29396626 82.50 10 000 35.90 11 774A 29406627 775 29446629 84 .OO 10.30 44 .OO 11 776 29516635 83 .OO 5 -80 26 .OO 11 777 2956 6639 9 e50 25 .OO 11 It 778 29616644 82 .OO 6.70 28 .OO 779 29686649 81.OO 6.80 30 .OO 11 29636649 81.50 8 .OO 28.00 11 780 11 781 29736653 78.50 6.50 39 .OO 11 29716653 79 .OO ?4.50 39 000 782 I1 -- 783 29716656 78.00 6.50 39 085 Deeside (North Wales) Thematic Geological Mapping 113

BGS Gri d Date of Surface Dri ft Engi neeri ng Number Reference drilling 7 eve1 thickness Depth properties

784 , 2970 6655 1975 79 .oo 6 -40 39 .oo Yes 785 29746655 II 7.20 40.55 If 786 2973 6658 11 78 .OO 7 .OO 41.OO II 787 29846656 II 78.00 7.50 39.85 11 788 2976 6660 11 78 .50 8.70 39 .50 11 789 29816664 11 78.50 7.80 41.50 11 790 29796663 II 78.50 9 .50 44 .oo I1 791 29786661 II 78.50 8.80 40 .OO II 792 29826662 11 78.50 8.90 40.30 II 793 29846669 11 77.50 ? 42.30 II 794 2983 6664 11 80 .00 ?24 .OO 40 -00 I1 795 29856665 II 80 .OO 11.35 42 -00 II 796 2987 6663 11 80 .OO 10.90 43 .70 It 797 29866660 I1 78.50 9 -40 50.35 I1 II II . 798 29836657 78.50 ? 50.15 799 29116605 II 89.50 ?3.40 25.00 I1 800 29026602 II 95 .oo 1.30 23.50 II 801 29056593 11 99.00 1.50 30 .OO II 802 I1 99 .oo 2 20 3 .OO I1 803 I1 96.50 1.70 3.90 I1 804 II 102.50 c 4.70 7 .60 11 805 11 101.50 5 20 8.30 I1 806 29186550 I1 100 .oo 4 .OO 15 .OO II 807 29206545 II 102 .50 4.10 25.00 II 808 29246536 11 108 -00 c 2.00 10 .oo 11 809 29296527 II 113.50 2.70 10.60 II 810 29326522 II 116 .OO 2.50 15 .OO I1 811 29376520 II 117.00 2.40 20.80 II 812 29416516 II 120 .oo c 9.50 24 SO I1 813 29396514 II 121.50 9 .50 27.50 II 814 29386513 I1 123 .OO 4 20 26 .UO I1 815 29426517 I1 117 .OO ?5 -00 55 .UO I1 816 29426516 11 119.00 6.50 23 .OO II 817 29406513 I1 121000 5.90 27 .90 I1 8 18 2943 6513 It 120 000 3.50 22 .oo II 819 29466509 II 119 000 11.70 27 .OO If 820 2950 6506 I1 114.50 3 -20 20 .oo I1 8 21 29576500 II 114.00 1.80 25.00 II 822 29576503 II 114 .OO 2.80 3.20 II 823 29576503 11 114.00 - 25 .OO I1 824 2956 6501 II 114.50 11.80 35 .oo I1 825 2956'6503 II 113 .OO 1.60 25 .OO II 826 29586500 11 113 .OO 2.90 25 .OO I1 827 25436609 - 20.12 I1 8 28 25536610 - 20.73 II 829 25616614 - 23.30 II 830 25836617 - 19.20 11 11 831 25916617 I 29.80 832 2598 6617 3.05 31.39 I1 1170 28786918 1984 39.07 4 .oo 4 000 II 1171 2896 6922 I1 38.62 4 .OO 4 .OO II 1172 29026920 II 37.20 3.20 3.80 I1 II 1173 2910 6914 It 35.40 4 .OO 4 .oo __ I1 1174 29506987 1982 5 -80 9.70 11 000 I1 1175 29566988 I1 6 .OO 18.90 19 .oo 114 Deeside (North Wales) Thematic Geological Mapping

BGS Gri d Date of Surface Dri ft Engi neeri ng Number Reference drillinp -1eve1 thickness Depth properties 1176 6.502962 6987 1982 20.20 20.50 Yes 1177 29676987 II 6.20 20 .So 20.50 II 1178 29736987 II 6 .So 21 .lo 21.60 II 1179 29796986 I8 6 .lo 21 .So 21.80 II 1180 29466982 1981 4.60 4.60 4.60 II 1181 2946 6981 It 3.50 4.00 II 1182 2952 6975 1977 5.70 5 000 5 000 II 1183 29496977 ll 5.80 5 000 5.00 It 1184 29486982 II 4.50 5.45 8.23 11 1185 2952 6986 II 4.50 7.72 14 .OO II 1186 29346951 1979 5 000 5 .OO 11 1187 2932 6960 11 4 000 4 .OO II 1188 29286976 II 2 .oo 2.80 I1 1189 2935 6987 II 0.80 2 000 II 1190 29536926 II 24.30 10.00 53 .90 II 1191 29496929 1978 23.30 8.40 22 000 II 1192 29446923 II 27 .go 16 .OO 40.00 II 1193 29396914 I1 33.20 18.80 22.50 II 1194 29456932 I1 24.00 8.00 12.40 II 1195 29356917 II 31.80 U.80 23 .So II 1202-1313 British Coal - Confidential

MAP SJ 26 SW

3 24186348 1934 C 103.63 13.41 122.83 8A 2470 6241 1879 18 .13 77.18 8B 2494 6190 II 45.18 8C 24836193 11 ? 18.90 8D 24506240 II 14.73 44.82 8E 24226162 II 8.23 31.39 8F 24086129 11 11.63 36.65 10 2111 6221 1957 ? 206.04 11 22986271 1975 144.50 13.60 29 .80 12 24126256 11 116 .OO 6 .So 27.60 13 24166256 1974 115.00 18.20 38.30 14 24296259 197415 106 .50 5 010 30.70 15 24286255 II 106 .SO 6.65 31.40 16 2431 6260 1974 106.50 5.50 27.30 17 24376262 II 106.50 9.50 31 .lo 18 24796311 197415 97 000 13 .OO 33.20 19 24826312 II 97.50 16.75 36 .OO 20 24786316 II 97 .50 14 .lo 34 000 21 2203 6476 1979 142 .OO 18 .10 18.10 22 22646473 II 122.00 17.80 17.80 23 22606375 135 .OO 13.30 13.30 24 22996264 1978 145 .OO 13 .OO 14 .OO 25 23336153 II 155.00 5.80 5.80 26 2355 6197 II 149.00 12.80 12.80 27 23666019 176 .OO 13.80 13.80 28 24006080 1978 148 .oo 12.20 12020 29 24246162 1979 142 .OO 8.80 10.70 30 24626271 II 107 .OO 20 000 20 000 31 24996355 II 100 000 6.50 8.00 32 23706001 1981 175 .O5 32.00 60.40 Deeside (North Wales) Thematic Geological Mapping 115

BGS Gri d Date of Surface Dri ft Engi neeri ng Number Reference drilling 1eve1 thickness Depth properties 33 1986007 2373 1 176.30 39.90 60 .OO 34 1311974 6456 2494 .OO 11 .oo 40.20 35 24986461 It 134 .OO 19.50 39 .50 36 25006463 It 134 .50 17.40 37 .OO 37-144 British Coal - Confidential 156- 182 British Coal - Confidential 185 6334 2392 c 109.00 8.70 154.30 239 621 137 186 621 239 .oo 18.14 77.11 187 606c 235 c 166.00 14.94 61 37 I 188 269196861002000 a 50 2.13 2.13 189 20206100 11 284.96 2.44 2.44 190 20346009 11 286.36 2.44 2.44 191 209.4020321967 6266 2.44 2.44 192 64112355 1979 10 .oo 10 .oo 193 23446403 11 10.oo 10 .oo 194 2351 6400 11 10 .oo 10 .oo 195 23476403 I1 2 .oo 2 .oo 196 23536403 11 2 .oo 2.00 197A 197663392421 5 30 5 .50 1978 2430 6340 I1 6.50 6 .50 197C 24256335 I1 6.50 6.50 197D 2422 6330 I1 6.50 6.50 197E 24306333 I1 6 .OO 6 .OO 197F 2436 6335 11 6.15 6.15 1976 2427 6325 It 5a50 5.50 198 24406326 It 4 .oo 4 .OO 199 2444 6333 II 4 .OO 4 .OO 200 24486329 I1 3.50 3 .50 201 24396319 it 6 -50 6 .50 202 2446 6320 It 4 .oo 4 .oo 203 24486316 II 4 .OO 4 .oo 204A 63282439 I978 8 .OO 8 .OO 2046 24416332 It 3.80 6.50 204C .24436331 I1 2.70 6.50 2040 24416328 II 4 a40 8 a00 204E 24436335 I1 5.50 5.50 204F 24476334 I1 3.30 4.50 205 2452 19796309 4 .OO 4.00 206 24546296 11 5.00 5 .oo II 207 24566287 11 4 .oo 4 .oo It 209 6287 2390 122.71 1983 13.50 13.50 II 210 23876284 It 118.81 7.30 7.30 It 211 23946281 II 117.38 6 .OO 6.00 I1 212 23956262 I1 121.12 2 000 2 .oo I1 21 2A 23956262 It 121..12 2 .oo 2 .oo I1 I1 11 212B 23956262 121.12 2.50 2.50 . 21 3 23926260 I1 122 a37 2 .oo 2 .oo II 11 213A 62602392 It . 122.37 2 .oo 2.00 II 214 24416268 11 111 21 6 .OO 5 .OO II 21 5 24436227 11 109.89 6 -00 6 .OO 24346266 11 110.88 6 .OO 6 .OO I1 216 I1 217 24356263 I1 106.43 7.40 7.40 217A 24356263 It 106 a43 5 .50 5.50 24336280 I1 104.64 10.70 15 .oo --Yes 218 11 219 2436 6281 It 103.83 14.60 45 20 I16 Deeside (North Wales) Thematic Geological Mapping

BGS Gri d Date of Surface Dri ft Engi neeri ng Number Reference dri 17 ing -1eve1 t hi ckness Depth properti es 220 24496272 1983 105.14 18.50 20.50 221 24346278 1984 8.90 30 .OO 222 24486275 1984/ 5 18.20 57 000 223 24336262 1985 8.90 10.50 224 24506324 1977 19.50 40 .OO 225 24506331 II 2%000 41 .OO 226 24456335 II 19.50 45 .OO 227 24046334 1976 109 .98 4 000 4 000 228 24056334 It 110.06 4.30 4.30 229 24076333 I1 109.87 4.50 4.50 230 24796400 1972 103.90 5.30 7.85 230A ? 2479 6400 I1 101.28 6.40 10.50 231 24806410 11 116.12 ?13 .lo 13 SO 232 24746412 II 119 001 5 090 7.03 233 24816418 I1 120 047 9.80 9.80 234 24846418 11 122.54 10 000 10 000 235 2480 6429 I1 127 .11 15.20 18 .OO 236 24836428 I1 127.97 11.60 14.60 237 24866428 II 129.38 10.30 10.30 238 2487 6439 I1 124.21 8.40 18.10 239 24886446 I1 123.78 6.60 18 .OO 240 24916456 II 130.85 6 .OO 6 .OO 241 22856261 I1 151.99 8.80 8.80 I1 242 22786276 * * 147.60 8 .OO 8.00 243 22746288 I1 145.27 7.50 7.50 244 22726294 I1 144.05 6.30 6.30 245 22996270 II 145 -05 10.50 10 .50 246 23136266 11 142.62 8 .OO 8 .OO 247 23426261 I1 135 -23 6 .OO 6 .OO 248 23556261 II 130.12 1.80 1.80 248A 23556261 II 130.12 1.80 1.80 If ' 2488 23556261 130.12 4.80 4.80 249 23716259 II 129.52 4 .lo 4.10 11 249A - 23716259 129.52 5.10 5.10 249B 23716259 It 129.52 4.30 4.30 249C 23716259 It 129.52 9.20 15.30 250 23866257 II 127.80 13.50 20 000 I1 251 24036256 , 120.90 9.60 18.00 252 24106255 II 116.34 ?6 .OO 18.00 252A 24106255 II 116.34 5.10 . 5.80 253 24186257 I1 112.98 22 000 25 .30 254 24306260 II 108.02 7.50 18.00 2 54A 24306260 II 108.02 7 020 8.70 255 24426264 11 105 .17 7.30 7.30 255A 24426264 II 105.07 14.70 14.70 256 24586270 It 105 .OO 20 000 21 045 257 2460 6273 I1 104 .96 19.50 19 050 258 24776299 II 98.72 11 -50 11.50 259 24786311 I1 97 95 13.40 13.40 260 2480 6315 II 97 099 16.50 16 -50 261 2480 6325 If 98 .OO 10 000 10 000 262 24786334 I1 98.16 10 -50 10.50 262A 24786334 I1 98.16 2.50 2.50 263 24756346 11 104.04 10 000 10 000 264 24736360 II 101.51 10 000 10 000 Deeside (North Wales) Thematic Geological Mapping I I7

BGS Gri d Date of Su rface Drift Engi neering Number Reference drilling -I eve1 thickness Depth properties 265 24826372 1972 99 037 8.50 10.50 Yes 266 24766384 I1 99.60 8.20 9.75 11 267 23206271 I1 136.66 6.40 6.40 I1 268 23566233 II 127.63 2.50 2.50 11 268A 23566233 11 127.63 3.80 3 .80 I1 2688 23566233 II 127.63 3 095 3.95 I1 . 269 2410 6256 II 109.88 7.90 20 .oo II 270 24216260 11 111.70 16 -00 17 .90 It 27 1 24286236 I1 106.59 1.00 1.00 I1 271A 24286236 II 106 -59 1.80 1.80 I1 27 1B 24286236 II 106.59 4.10 18 .OO 11 316 24676293 1981 11 000 30 -00 317 2473 6303 11 16.80 30.00 318 24576275 II 15.60 30 .00 319 2463 6283 II 15.10 30 .OO

MAP SJ 26 SE 1 c 2537 6307 19 37 ?17.72 99 .36 1A 1939 ?13.87 67.06 5 2684 6491 c 136.55 8.71 62.15 9 10.67 78.69 10 28516086 1927 12.34 12.34 16 26366180 1955 99 .97 4 -57 333.14 17A 26246460 1975 158.702 010 15 .00 17 0 26366461 II 154.30 2.10 10 -50 17 C 26286466 ll 154.60 1.50 16 .00 17D 26326455 It 156.40 3 000 16.80 17 E 26306459 It 156.40 1.80 16 .20 17F 2625 6456 I1 . 158.50 2 080 15 .OO 17G 26346464 tt 154.90 2.10 21 .oo 17H 26216468 11 155.80 2.90 15 .OO II 17 I 26786469 153.50 1.80 23 .OO 9 II 17J 26366464 153 .OO 1.50 7.70 9 17K 26436458 II 152.20 2.10 21 000 -. 17L 26376458 II 155.202 -40 11 000 17M 26356458 11 155.80 2 010 22 000 17 N 26376455 I1 154.80 1.80 18 .00 17/ 0 26366458 II 155.502 020 10 000 17P 26376458 I1 155.20 2 020 10 000 If 17 26386467 151.60 2 000 12 .oo Q II 17 S 26496457 2.40 19 000 I 17T 26526460 I1 5.30 22.50 17U 26506462 II 4 .OO 18.00 17V 26326446 I1 4.30 20 .oo 17W 26406449 11 3 000 15 .oo It 17X 26456441 3.40 8 .OO I 17'i 2648 6452 II f .80 8.00 II 17 2 26726448 3.40 17 .OO I 18 25256483 II 146 -50 20.40 40 .OO 19 25526498 II 152.00 10 *lo 32.90 20 2990 6468 1972 116.31 Ni 1 2.16 Yes 21A 29516362 1975 124.30 c 3.00 31.OO '- I1 It 21B 29526359 I1 124.20 4 .00 8.40 118 Deeside (North Wales) Thematic Geological Mapping

BGS Gri d Date of Surface Dri ft Number Reference drilling -1eve1 thi ckness Depth

21c ' 29536356 1975 124.60 4 000 6.30 II ' 21D 29496361 124.90 4 -00 6.30 21E 29496358 I1 125.20 3.50 7 .So 21F 29506355 II 125.60 3.26 30.00 21G 29466360 I1 126.40 3.80 30 .SO 21H 29466357 I1 126.90 4.60 7.70 21I 29476354 I1 127 .OO 4.70 7.30 215 29436362 I1 128.50 6.90 9 .So 21K 29506351 II 125 .OO ?3.80 5.70 21L 29506346 II 123.80 3.20 5 020 21N 29506352 11 124.80 4 .So 30 .OO 21/0 29496349 II 125.30 ?3.80 34.00 21, P 29476348 I1 125.40 6.40 35.00 214 2952 6347 I1 123.70 3.50 20.80 23 25556483 1979 155 .00 4 .So 5.50 24 25356304 II 122 .OO 13.80 14.50 25 25186074 II 148 .OO 13.00 13.10 26 25616207 I1 95 000 19.50 20 .00 27 26446309 I1 144.00 11 000 11 .So 28 26756245 I1 100 000 18.70 19.30 29 26806212 I1 97.00 22.50 22 -50 30 26586061 II 166 .OO 16 .OO 16 SO 31 27726277 11 113.00 16 .2O 16 20 32 27666160 II 96.00 23 .So 23.80 33 28566250 II 114.00 16 .OO 16 .OO 34 28526108 I1 98 .OO 18.50 18.50 35 28716037 I1 ?93.00 14.00 14.00 36 29586305 I1 121.oo 7.20 8 .OO 37 29266089 11 86 .OO 18.30 18.30 38 29906233 II 115.00 4 000 5.20 39 25646218 1948 97.23 12.19 12.19 40 25426208 II 99.35 10.97 10.97 41 25436224 I1 98.40 9 .I4 9 .I4 It 42 - 2543 6248 96.74 14.33 14.33 43 25486223 II 98.17 13.41 13.41 44-489 . Bri ti sh Coal - Confidential 512 c 25306274 70.56 513 c 25696253 65.07 514 c 2573 6265 34.82 515 c 25406293 89.18 529-545 British Coal - Con fi dentia 7 546A 29276303 1971 120 000 546B 29276303 I1 120 .oo 11.40 100 000 547 2849 6327 I1 134 .20 13.00 100 000 548 28496347 I1 134.30 12.40 62 .OO 549A 28526325 II 122.70 14.20 42 .OO 5498 28516325 II 133.10 10 000 68.00 550 28576325 II 133.70 10 .oo 100 000 551A 27536155 I1 93.80 10 000 103.00 551B 27536155 II 93.80 10.30 57 .go 552 27516153 II 93 .30 12.40 21.40 553A 26626107 It 170.80 3.50 94.00 5530 26626107 II 170 -70 3 .so 68.40 554A 26286474 II 151.10 3 .oo 100 000 554B 64742628 I1 151.lo 3.50 44.40 Deeside (North Wales) Thematic Geological Mapping 119

BGS Grid Date of Surf ace Dri ft Engi neeri ng Number Reference dri 11ing 1 eve1 thickness Depth p ropert i es

* 555A 2644 6020 1971 170.40 6.40 52 .OO - 555B 2647 6019 11 169.40 5.40 94eOO - 555c 2648 6019 II 169.50 5 .OO 92.00 - 556A c 284 610 2 -90 18.29 - 5568 c 284 610 3.66 19 020 - 556C c 284 610 12.37 12.37 I 557 2999 6076 1982 111.66 5 000 5 -00 Yes I1 II ' 558 2998 6080 112.37 5 e00 5 000 559 2998 6082 I1 112e56 5 000 5 e00 11 560 2995 6083 II 110.98 5 000 5 .OO II 561 2992 6088 II 107.52 5 e00 5 .OO II 562 2990 6088 II 106 e64 5 e00 5 000 II 563 2991 6091 II 106 e35 5 eo0 5 .OO I1 564 2989 6092 II 106 e93 5 000 5 .OO II 565 2988 6094 II 106 e94 5 000 5 000 II 566 2986 6095 II 108.03 5 000 5 000 II 567 2982 6099 II 108.11 5 000 5 .OO I1 568 2979 6103 II 108.21 5 000 5 000 11 569 2975 6109 II 108.03 5 .OO 5 .OO II 570 2972 6115 II 107.34 5 000 5 .oo 11 571 2970 6122 I1 106 e58 5 000 5 .OO I1 572 2968 6130 II 106.65 5 e00 5 .OO 11 573 2968 6140 11 103 e71 5 000 5 e00 II 574 2968 6146 II 102.66 5 000 5 .oo II 575 2970 6150 II 102.51 5 000 5 .OO II 576 2973 6159 II 105.62 5 000 5 e00 II 577 2975 6165 II 106.72 5 000 5 e00 II 578 2978 6168 II 106.08 5.00 5 .OO II 583 2951 6141 II 101.52 0.70 2.00 II 584 2925 6109 I1 84.86 5 000 5 .OO II 603 2719 6231 604 2722 6162 605 2722 6210 32 .OO 606 . 2717 6201 34 .75+ 608 2645 6404 3.35+ 609 2642 6393 10 e06 615 2587 6004 616 2524 6175 44.81 617 2530 6174 43.89 633-638 British Coal - Confidential 644 2956 6300 c 3.66 645 2957 6280 646-739 British Coal - Confidential 763 2655 6080 68.58 765 2650 6109 766 2629 6096 767 2662 6105 ?42 e06 768 2796 6097 [British Coal "Shaft" No 2771 80 7 2786 6066 14.63 808 2761 6074 27.43 809 2788 6026 81 0 2792 6027 [Possi bly same borehole as No 8091 2794 6189 54.86 6189835 2794 -- - 2748 6141 56.69 6141 83 6 2748 - 2675 6113 31.09 6113 863 2675 - 120 Deeside (North Wales) Thematic GeologicalMapping

BGS Gri d Date of Surface Drift Engi neeri ng Number Reference dri 11 ing, 1 eve1 thi chess Depth properties

864 26746112 31.09 885 29076364 9.14 886 29116364 894 29876401 38.10 904 . 28696348 [British Coal "Shaft" No 581 - 10111972 6464 2500 136.16 5.70 5.70 Yes 1012 25076472 I1 139 .22 4 .OO 6.30 I1 II II ~ 1013 25156480 142.12 2.50 6.30 1014 25246484 I1 12.00146.36 12.00 II 1015 25346491 I1 150.33 11.30 12.50 11 1016 25506499 I1 152.03 11 010 11.60 II 1017 197564952966 111 000 Ni1 11.70 I1 1018-1043 British Coal - Confidential

MAP SJ 27 NW

1A 194777112015 18.28 18.28 1B 20207718 I1 18.28 18.28 1c 20207748 I1 18.28 18.28 1D 20277754 II 18.28 18 28 4 British Coal - Confidential 8 19867557 2070 c 67.00 9.30 12 000 Yes 9 19732075 7724 6.85 5 .OO 5 .OO I1 10 20787713 I1 4.30 4 .OO 4.00 I1 I1 11 11 20887717 1e10 5 .OO 5 000 12 20847712 I1 4.15 4.50 4.50 I1 13 20807707 It 4.85 12.00 12.00 I1 14 20767704 I1 4.05 12.00 12.00 I1 15 20707698 II 4 .25 4.50 4.50 I1 16 20647680 II 4.40 4.50 4.50 I1 17 20617687 I1 4 045 4.50 4.50 II 18 20517676 I1 6.15 4.50 4.50 I1 19 20457676 I1 5 075 4.50 4.50 If 21 20387678 I1 10 090 5 000 5 000 11 23 20297669 I1 17.45 5 -00 5 .OO II 24 20337661 I1 15.70 3 .OO 3 .OO I1 25 20317654 II 16.30 2 000 2 000 I1 26 20207664 11 26 .OO 4.50 4.50 II 27 20147664 li 28.50 3 -00 3 000 I1 28 20067656 II 45.05 2 000 2 000 I1 29 20127650 I1 47.10 2 000 2 000 It 30 20827695 11 3.80 3 000 3 .OO II 31 20777690 11 3 075 3 .OO 3 000 I1 32 20867687 I1 3 090 3 .OO 3 .OO I1 33 20127700 I1 13.45 7 .OO 7 000 I1 34 20147702 I1 9.60 5 000 5 .OO 11 35 20177703 I1 5 .25 5 000 5 000 It 36 2019 7706 11 4.65 4.50 4,50 I1 37 20257698 If 4.60 4.50 4.50 I1 38 20327690 I1 4 .BO 4.50 4.50 11 39 20387683 I1 4.85 4.50 4.50 II I1 I1 40 20117714 4.50 4.50 4.50 -_ 41 20047724 11 5.15 4.50 4.50 II- 42 20017720 I1 4 075 5 000 5 .OO I1 Deeside (North Wales) Thematic Geological Mapping 121

BGS Gri d Date of Surface Dri ft Engineering Number Reference drilling 1eve1 t hickness Depth properties ~~ ~~ 43 21887518 1973 20.40 7.30 34.50 - 44 21927522 II 12.20 5.50 29.00 - It 45 21897523 1 17.80 9 .lo 33.50 - 46 21897515 It 21.70 7.30 22.00 - 47 219775334 1985 .OO 4.00 Yes It 48 21817546 6 .OO 6.00 'I II 49 21597570 6 .OO 6.00 I' II 50 20377707 4 .20 5 000 5.00 It 11 51 20477698 3 4.50 .OO 3.00 I' It 52 20547690 3 4.80 .OO 3.00 It II 53 20537696 4.50 3 .OO 3.00 I' II 54 20467704 4.50 3 .OO 3.00 It 55A 2197 7515 23.40 1972 2 074 5.30 I' It 55B 21967516 22.90 6 -40 10.30 I' II 55c 21957520 18.90 9.50 10.59 I' II 55D 21937517 519.50 000 6.70 I' II 55E 21967518 6.40 18.90 8.15 I' 11 55F 2199 7515 6.50 23.80 6.50 I' II 55G 2197 7511 4.10 26.40 6.30 I' II 55H 2195 7513 ?4.1525.40 10.05 I' ll 551 21907514 -70 19 4.60 7.05 I' II 555 2189 7518 20 -80 c 4.40 5.58 I' I1 5% ' 2190 7521 9.30 16.60 11 .50 'I. II 55 L 21927522 15.SO 11.80 12.57 'I II 56 21927525 -6015 12.00 12.40 I' II 57 21957527 10 010 10.50 11.50 I' II 58 21947534 6.40 10 .oo 10.50 'I II 59 21947539 4 .OO 18,OO . 18.00 I' 60 21897541 II 5 .20 10 000 10.00 61 21887545 II 4.60 10 000 10.00 62 22207540 1973 10 000 10.00 It 63 22307530 II 10 .oo 10.00 II .64 22387520 10 000 10.00 'I II 65 . 22387534 10 000 10.00 'I II 66 22347533 10 000 10.00 II II 67 2226 7543 10 000 10.00 It 68 21087647 II 10 000 10.00 140 2055 7643 ?128.00 - 144 21887518 1978 7 000 27.00 - 145 21737504 It 9 000 24 .OO - 146 21807509 It 5 .50 36.60 - 147 2155 7523 II 49 .85 16.00 1.70 - 148 21597528 II 44.70 3 .OO 35.00 - 149 21637532 II 39.90 4.30 20.00 - 150 21607524 II 44 .74 7 000 30,OO - II 151 2164 7523 41.39 5 000 28.00 . 152 21727524 II 35.64 7 .OO 15.00 - 153 21837534 II 21.05 15.60 7.60 - 154 2174 7538 II 29.45 7 050 32.00 - 155 2197 7523 II 9.80 9.80 - 156 2162 7530 II 40.58 5.50 14.00 - 157 2171 7536 II 31.94 7.60 18.00 - 158 21987508 1979 1.oo 30.00 .. 159 2200 7513 II 1.00 30 0.0 -- - 160 21857540 1978 10.50 30.00 - 122 Deeside (North Wales) Thematic Geological Mapping

BGS Gri d Date of Surface Dri ft Engineering Number Reference drilling -7 eve1 thickness Depth properti es 161 21867541 1978 9 000 30 - I1 .OO . 162 21887541 c 3.00 30 i I1 .OO 163 21887543 11 000 30 0 II .OO 164 21887545 c 3.00 30.00 0 I1 165 21967537 9 000 30 .OO 1 I1 166 22027529 c 6.00 30.00 0 I1 167 22037532 9 000 30 .00 0 II 168 21967524 3 000 30 0 11 .OO 169 21987526 c 6.00 30 .OO 1

MAP SJ 27 SW 2 23617154 1912 36.58 40.23 233 .78 3 -2468 7036 1935 21 -34 21 034 21 2427 7290 11 -89 6.25 7.77 22 24277308 10.67 3.05 24.39 23 24347314 8.84 3.20 24.39 24 24307295 1968 11 074 3.30 5.74 25 24377286 I1 14.01 3.81 7 -42 26 24467292 I1 10.50 7.32 9.82 27 24447303 I1 8.90 7.62 10 001 28 24327292 I1 12.09 3.66 17.99 29 2441, 7292 I1 11.18 2.59 6 020 30 24507300 I1 8.65 7.60 9.34 31 24447297 I1 9 074 6.10 18.29 32 24347293 1970 1.07 60 .96 36 24777408 11 0.91 23.09 25.15 43 20427268 1972 172 20 6 .OO 6 .OO 44 20437263 If 172.30 6 .OO 6 .OO 45 20427261 II 174 .70 6 .OO 6 .OO 46 20487260 I1 169.30 10 000 10 000 47 20467259 I1 170.80 15 .OO 15 .OO I1 48 - 2046 7259 170.80 15.00 15 .OO 49 20447258 II 172 20 10 000 10 000 50 20437256 11 173 -70 10 000 10 000 51 20467257 11 171.60 10 000 10 000 52 20477258 I1 169.80 11.80 11 080 53 20497259 11 168.90 10 000 10 000 54 20477252 II 174.40 10 000 10 000 55 20507254 II 171.20 6.50 6.50 56 20567245 11 173 .lo 5 000 5 000 57 20657235 11 169.30 6 .OO 6 .OO 58 20347279 11 176.20 4 000 4 000 59 20287291 II 178.80 3 000 3 .OO 60 20237302 I1 180 .30 3 .OO 3 .OO 61 20187312 II 183 .OO 4 .oo 4 .OO 62 20127322 11 179.70 4 .OO 4 000 63 20067334 II 181090 4.00 4.00 64 24677297 1973 8 -05 4.60 7 .20 65 24687298 I1 8.00 5.20 7.80 66 24707296 11 8 045 4.50 6.50 67 24707296 II 8.45 4.50 25 .OO 68 20917203 1976 5 000 5 000 69 21067184 I1 4 .OO 4 .OO Deeside (North Wales) Thematic Geological Mapping 123

BGS Gri d Date of Surface Dri ft Engi neering Number Reference dri 11i ng level t hi ckness properties 70 21347146 1976 5 a00 5 000 Yes II ’ 71 2145 7132 5 e00 5 a00 II 72 22147061198 1 152.62 3-80 6 .OO II 73 2228 7046 II 152a61 5 045 5 045 II 74 2229 7048 I1 154.43 2 000 5 20 II 75 2236 7039 II 147.80 3 a90 5a15 II 76 2238 7040 II 149 -93 4.50 9 a00 II 77 2235 7038 II I50 .OO 2.45 6 .OO II 78 2248 7027 II 146.46 3 .oo 4 .lo II 79 2246 7024 II 145.18 5 -40 7 .OO I1 80 2253 7019 I1 146 .36 1.00 12 e00 II 81 2253 7022 II 144.74 0.30 1 a00 II 82 2251 7018 II 142.57 2.90 9 000 II 83 2266 7010 II 133 a67 5 000 5 .OO 11 84 2265 7008 11 137 a39 c 1.50 7000 II 85 2277 7001 II 123.83 5 .oo 5.00 I1 86 185.951978 7302 2013 8.OO 13.20 II 87 2048 7356 II 107.92 13.60 19.00 II 88 2032 7377 II 178.04 19.80 19.80 11 89-238 British Coal - Confidential 246A 216373611986 c 108.00 7.80 7-80 Yes II II 246B 2163 7361 c 108.00 7.70 4 8.20 247 2377 7105 II c 67.00 25 .OO 25.00 II 245 2267 7312 II c 84.00 ?25 .OO 25 .OO It 249 2495 7057 II c 69.00 11.20 11.20 II 250 2169 7060 II c 183.00 2 020 3 020 251 2073 7235 II c 167.00 12 000 12 000 252 2039 7322 II c 172.00 7.60 8a80 2538.23 1976 7317 2440 3.50 22.00 254 2439 7315 11 8.51 3.20 22 000 255A c 24227294 1964 4 a26 6.40 2558 c 2422 7294 II 6.25 7077 255C c 2422 7294 II 7.16 9 075 2550 c 2422 7294 It 4.63 6.10 256 23927326 1981 ? 17 .OO 18.00 257 2389 7335 II 6 .OO 6.OO 258 2387 7330 II 6 a00 6 .OO 259 2382 7326 II 5 000 5 000 260 2388 7323 I1 6 .OO 6 .OO 261 2391 7318 11 6 -00 6.00 262 2396 7314 11 6 a00 6 .OO 263 2393 7309 II 6.OO 6.00 264 2388 7306 - II 6 .OO 6 .OO 265A c 24097338 1985 13.10 13 .lo Yes 2658 II II 7.50 7.50 II 265C If I1 7 a40 7.40. It 265D II II 7.60 7.60 11 265E It II 13.50 30 .OO II 265F II #I 13 .OO 24.00 11 2656 II II 12.50 23.10 It 12.10 12.10 II 266 16.111982 7304 2388 II 267 2396 7304 I1 11 091 12 a00 12 000 11 loa77 6.50 6 a50 II 268 2390 7312 I1 II 15 .OO 15 .OO 15.00 __ 269 2383 7317 11 270 2378 7326 II 13.65 1 a16 1 a-16 I24 Deeside (North Wales) Thematic Geological Mapping

BGS Gri d Date of Surface Dri ft Engi neeri ng Number Reference drilling -1 eve1 thi chess Depth properties 270A 23787326 1982 13a65 11 a00 11 m00 27 1 2384 7371 I1 10 mol 12mOO 12a00 272 23997294 I1 10 a00 7 a40 10 m08 274 23697356 1981 . 7 a05 18.00 275 23757356 11 19 m20 30 a13 27 6 23807358 c 57a90 70 a00 277 23787338 28 a90 42 a65 278 23817334 32 a45 43 a 00 283 23497375 10 .oo 284 2377 7364 15m00 285 23957351 10 a00 286 23357365 10 a00 287 23567337 15a00 288 23717340 10 a00 289 23857328 10 a00 290 23897301 10 a00 29 1 22497498 1976 9 a00 9 a00 292 22537491 If 8 a00 8 m00 293 2260 7487 11 8 .OO 8 a00 294 22597481 11 8 a00 8 m00 295 2267 7481 II 8 a00 8 a00 296 22697472 II 8 a00 8 .OO 297 2276 7473 I1 8 a00 8 m00 298 22757467 II 8 a00 8 m00 299 22817462 I1 8 a00 8.00 300 c 22957454 II 9 a15 9 a15 301 c 22897453 11 9.15 9 a15 302 c 2282 7463 II 9a15 9.15 303 c 22967450 I1 7 m79 7a79 304 c 22907456 I1 8a38 8.38 305 24827314 1974 5 m74 7 a35 9 a05 306 24817303 II 6 a04 1a45 5 a00 24947292 II 6 a72 5 a75 7.90 P" P" 307 309 2350 7313 1984 19a62 3 a80 5 m80 I1 310 23587317 19 a 75 2a90 5.10 311 2367 7320 II 16 a96 6 a25 6 a25 312 23537308 II 19 a75 3-60 6 a07 313 23597310 I1 Om50 2 a40 314 23667310 II 7 a50 7.50 315 23717317 I1 6 a20 6 a20 316 23557302 II 19 a76 Om30 2 a26 317 23707308 I1 6 a20 6.20 318 23547296 1983 25a39 10 a75 10.75 320 23757202 II 10 a00 10 a00 321 2360 7293 I1 22 a82 4 a40 6 a00 322 23677293 It 20 a57 6 a05 6 a05 323 23757294 II 1 m67 1a67 323A 23757294 I1 10 a05 10.05 324 2390 7297 II 13.68 10 .oo 10 000 325 23627284 I1 26 a67 1m30 5.55 326 23747290 II 18 m14 21 a25 21.25 327 2370 7281 I1 24m30 6 a45 6 m45 3 28 23797286 11 16 mO9 10 a65 10 a65 329 23937288 II 13.06 12.45 12a45 330 23767275 11 22 a26 8.50 8.50 Deeside (North Wales) Thematic Geological Mapping I25

BGS Gri d Date of Surface Drift Engineering Number Reference drilling -level thickness Depth DroDerti es 331 23827276 1983 17 e33 8e45 8 e45 Yes 332 23957289 II 13e68 10 e45 10 e45 iI 333 23817309 II 8.10 8 e10 11 334 23897336 1981 3 9e73 e05 3 e05 11 - 335 23947340 3 I1 e58 6 e00 II 336 23937335 11 9 e55 12e50 II 337 23967332 I1 9 e67 12e50 II I1 338 23907327 10 e85 * 15.05 339 23957326 10 e27 15e45 11 340 23957319 10 e68 12 e00 11 341 2397 7345 6 e12 3 e00 11 342 c 244738 1985 Boreholes in tip, up to 15 m 347 23337351 ? 10 e40 11.30 348 23587356 ?9 e00 11 e50 349 23767370 9 e50 9.50 350 23987354 14.50 14 e50 351 23817346 ?22e60 30.30 352 23607326 8 e00 23 e00 353 23887328 25 e25 25 e25 355 23267426 1974 9 e10 7 e80 9 e60 Yes 356 23297423 I1 4 8.30 e50 6 e10 I1 412 22317465 1978 2 e20 13.80 41 3 22347468 11 - 16 e00 I1 414 22287463 3 .oo 28 e 00 415 22357464 11 1.oo 26 e00 416 22337461 3 e00 52 e00 417 22367458 1e50 23 e00 418 22157492 1.80 18 e00 419 22307499 4 e60 20 e00 420 22017490 1974 2 e80 18 e30 424 23137312 ?36.58 ?36e58 425 2281 7250 c 9.14 c 9.14 43 5 23927091 26-52 26 e52 436 . 24997120 15 e24 15 e24 43 7 24997108 12.19 12.19

MAP SJ 27 SE 1 2776 7058 c 9e14 62e17 - 2A 2616 7161 123.75 - 2B c 71502628 ?1943 114.78 3 CeEeGeBe - Confidential 4 c 70872643 - 38.25 - 5 7035 2850 4.87 1939 2.79 4e57 - 9-15 British Coal - Confidential 16-30 CoEeGeB. - Confidential 35 2561 7370 1970 7370 2561 35 0 e46 ?20 e73 21 e03 Yes I1 11 43 74772603 Oe30 30 e 48 30.48 46B 73262650 II 2 e41 21 e34 21 e34 61 2751 73742751 61 II 2 e59 15 e24 15 e24 64 72482777 I1 2 e32 20.27 20.27 66 71702806 I1 3e87 25 e45 25 e45 11 79 2902 7224 5 e06 18 .29 18.29 -- 95 2896 95 5 1978 7223 e41 15 e45 15e45 I26 Deeside (North Wales) Thematic Geological Mapping

BGS Gri d Dateof Surface Dri ft Engineering Number Reference drilling 1eve1 thickness Depth ProDerti es 96-166 British Coal - Confidential 175-176 British Coal - Confidential 177 19867072 2545 c 57eOO 17e10 17 .lo Yes 211-213 CoEeGoBe - Confidential 214 28467034 1984 6 e38 3 e30 4.70 Yes I1 II 215 28547028 6 e57 4.60 5 .OO 216 28507033 II 5 e39 3.50 4 -00 II 217 25027289 1974 6 e51 4 e10 6 e00 If 218 27397260 1983 2 e66 20.00 20 000 II If II 219 27117273 1e79 20 e00 20 e 00 220 27287291 II 1.75 20 000 20 000 II II 11 221 27687262 2 e55 20 e00 20 eo0 222 27487240 II 3 e84 20 e00 20eOO 11 223 . 27217284 II 1e61 20 eo0 20 000 II II II 224 27497279 1e71 20 000 20 e 00 225 27587251 11 3 e14 20 e00 20 000 11 I1 II 226 27297257 2 e87 20 e 00 2OeOO 227 26977265 11 1.54 20 eo0 20 e00 I1 228 26867275 I1 1.I6 20 e00 20 e00 11 229 26967287 I1 2e37 20 .oo 20 e00 11 230 2784728% 11 2.43 20 e00 20aOO 11 231 26747292 I1 2 e63 20 000 20 e00 11 232 27007277 11 1e68 20.00 20 .00 11 233 27287278 II 1e84 20 e00 20 e00 II II 11 234 27177261 2 e33 20 000 20 e 00 235 27247261 II 2.31 20 e00 20 000 I1 236 27357282 It 1e82 20 e00 20 000 It 237 27447254 II 2.94 20 e00 20 e00 I1 23% 27547265 I6 2 e89 20 e00 20 e00 I1 239 27627241 I! 3 e59 20 000 20 .00 II 240 27707250 11 3 e38 20 000 20 e00 I1 I1 II 241 27787260 2 e00 ZO eOO 20 e00 242 27107280 II 1.19 20 e00 20 000 I1 11 11 243 - 2734 7262 2 e80 20 000 20 e00 244 27447274 11 2 e58 20 000 20 000 II 245 27907257 I1 1e93 20 e00 20 000 11 246 28087247 11 2.44 20 e00 20.00 I1 247 27907242 II 3.85 2OeOO 20 e00 11

MAP SJ 36 NW 1 69743091 ?1913 3.66 43.89 67 e67

2 69943116 1905 ' ?3.66 48.01 66.85 3 ? 31706966 ?4.57 ?62.58 4 69733186 189 1 c 6e10 46.89 179.98 Boreholes 3 and 4 may be the same 5 ? ?1820/3068373382 c 6.10 91.44 91.44 3228 6813 18917 6813 3228 5.49 44.81 225 20 86701 3331 5 049 50 e29 85.80 9 19006751 3393 c 5-49 43 .13 44 e04 10 67483332 c 5.18 11 67493333 5 e18 59 e59 209 e 22 12 3383 67023383 12 c 5.18 59 e40 204 e80 13 3338 66703338 13 c 5e18 92.68 Deeside (North Wales) Thematic Geological Mapping 127

BGS Gri d Date of Surface Drift Number Reference dri 1 ling 1eve1 t hichess Depth 14 3326 6814 43 e97 113e94 15 3114 6997 1913 51 e66 61 e 37 21 ? 1853 7e92 91 e74 24 c 328 688 '59 e44 72 e54 25 3280 6874 1957 67 e06 76 e20 26 3202 6572 1913 c 53e34 26 e97 141 e63 27 3202 6572 1911 27 e74 51 e21 28 ? 3394 6539 1890 c 9e14 15e24 15 e24 29 3466 6630 c 10e67 50 e90 51 e82 30 c 316 664 130 e20 31 3314 6540 ? 1862 38 e40 124 e59 32 3288 6516 ? 1862 c 33.53 23.47 120.88 33 3339 6512 ? 1862 c 19.81 40 e23 163.85 34 3405 6561 1862 c 6e10 69 e49 69 e 49 35 3321 6566 ?1862 15 e24 39.62 73e30 36 3371 6516 1862 c 12.19 59 e44 77.24 37 3331 6592 ? 1862 c 12.19 36 e58 179 e58 38 3352 6586 ?1862 c 9.14 46 e79 124.08 39 3179 6614 26 e97 101 e73 40 3167 6654 91.14 43/ 1 3021 6926 1961 4 e26 6.10 6 e10 II 43/ 2 3019 6924 4.34 6 SO * 6e10 431 3 3011 6929 II 4.69 3 e05 3 e05 43/ 4 3019 6913 II 9 e44 3e66 3.66 431 5 3000 6915 I1 6.70 1 e98 1 e98 43/ 14 3030 6936 11 4.26 3 e05 3 e05 43/15 3028 6938 I1 4 e26 6.10 6 e10 43/ 16 3032 6937 II 4e26 4 e88 4 e88 431 17 3035 6938 I1 4e26 1.52 1 e52 11 43/ 18 3030 6940 4.26 1 e52 1 e52 43/19 3033 6941 II 4 26 6.10 6 e10 43/20 3026 6942 II 4 e26 7.62 7 e62 441 1 3018 6914 1959 7.92 3 e20 3 e66 It 441 2 - 3021 6914 5 a49 2 e67 2 e82 441 3 3021 6911 11 6 e71 3 e35 3 e51 441 4 3021 6907 II 6 e45 2 e29 3.05 4415 3018 6904 II 6e71 1 e83 2e26 44/ 6 3016 6902 11 7 e16 3.35 3 e78 441 7 3014 6902 I1 8 e84 5.94 7.60 I1 44/8 3010 6904 11 e58 10 a 21 10 e36 451 1 3227 6846 1960 7.01 22,86 22 e86 45/ 2 3275 6883 II 81.56 6.10 6.10 45/4 3008 6678 11 82 e30 10 e06 10.06 4515 3018 6684 II 78.58 12e19 12.19 45/ 6 3007 6683 II 81 e44 9.14 9.14 451 7 3003 6680 11 83 e61 11 e28 11 e28 4518 3001 6674 11 83.70 10 e67 10 e67 4519 3015 6681 11 81 e08 10 e67 10 e67 45/10 3019 6679 11 74 e07 10 e67 10 057 47111 3026 6678 11 78.49 9 e14 9 e14 45/12 3029 6691 II 63 A2 9 e14 9 e14 451 13 3023 6688 I1 72.79 11 e58 11 e58 45/14 3014 6689 IJ 77 -52 6 e10 6.10 451 15 3035 6683 If 75 e83 6e10 6.10 45/ 16 3035 6677 II 78 e24 11 e58 11 e58 128 Deeside (North Wales) Thematic Geological Mapping

BGS Gri d Date of Surface Dri ft Engineering Number Reference drilling -1eve1 thickness Depth properties 45117 30386677 1960 76 a35 10 a97 10 a97 451 18 30396679 II 71 a24 4 a57 4 a57 45119 31336786 11a13 6 a10 6.10 45/20 31306784 11 a89 6 a10 6a10 45/21 31486795 7 a47 6 a10 6a10 45/22 31796805 5 a21 4.57 4 a57 45123 31926808 5 a09 6 a10 6 a10 45/24 32236846 5 a03 17 a 30 17 a 30 45/25 33176930 4 a48 6 a10 6a10 45/26 33156923 4 a57 6 a10 6a10 45127 33146914 1960 4 a54 6a10 6 a10 45128 30476705 1961 5 a08 18.29 18 a29 I1 45/29 30446703 51a25 18a29 18 a 29 I 45/30 30436704 I1 51 a25 11 a13 11 a13 451 31 30456702 51.51 10 a36 10 a36 45/32 30466706 50 a02 9.45 9 a45 45133 30486704 50.06 9.45 9.45 - 47/A1 33236937 1971 4-33 12.95 12.95 Yes It I1 47/ A2 33216936 4 a48 12 a 19 12.19 47/A3 33226938 I1 4 a48 12.19 12.19 II 47/A4 3324 6936 I1 4.30 10 a67 10 a67 I1 47/A5 3325 6937 II 4.27 12a50 12 a50 I1 4711X 33236936 11 4 a30 20 a42 20 a42 11 47/A6 33276925 I1 4 a36 6.10 6 .lo If 47/A7 33296929 11 4 a15 9 .I4 9 a14 I1 4711 33216931 11 4 a66 3.96 3.96 II 4712 33286948 If 4 a57 3.96 3 a96 I1 4713 33296957 II 4a60 3 a96 3 a96 It 4714 33326967 I1 4 066 3 a96 3 a96 11 4715 33326973 II 4 a85 3 a96 3.96 I1 4716 33376982 I1 4 a66 3 a96 3 a96 I1 48 31486795 1973 8 a22 15a45 15 a45 I1 49 31606803 II 6.34 10 a00 10 a00 11 50 31596794 11 6 a90 10 a00 10 a00 I1 I1 I1 51 31716799 6.84 30 a00 30 a 75 52 31796804 II 6a33 25 a00 25 a00 11 53 31866806 II 5 a48 15 a00 15aOO II 54 31936813 I1 5 a48 15 a00 15 a00 II 55 31576793 1974 7 a19 ?25 a00 45 a00 II 56 31716796 If 5 a36 28 .OO 49 a00 I1 I1 57 31536791 c 8.20 20 a 50 20 a50 58 31616791 I1 c 6.40 c 24a20 25 a40 59 31646792 I1 c 5a50 16.40 16 a40 60 31696796 I1 c 5a30 20 a20 20 a20 61 31756796 II c 6a30 15 a40 15 a40 II 62 31766799 C 7.00 20 a10 20 a 10 63 31806798 I1 c 6aOO 15.30 15.30 64 31846806 It c 5a05 5 a00 5 a00 65 3165 6814 I1 c 6.00 5 .OO 5 -00 66 31656808 I1 c 6.15 5 a40 5 a40 67 3162 6801 11 c 5a85 5 a00 5.00 68 31666786 I1 c 7aOO 5 a20 5 a20 69 30246687 1972 71a89 15 a30 15a30 70 30796661 I1 65 a02 8 a80 8 a80 71 31136644 II 56a30 10.50 10.50 Deeside (North Wales) Thematic Geological Mapping 129

BGS Gri d Date of Surface Dri ft Engineering Number Reference dri 1 ling -1 eve7 thickness Depth properties 72 19726627 3145 51a13 15 a00 15 a00 73 32226583 II 39.60 8.10 8 a10 11 74 32546533 41 a 17 9.30 9.30 751 1-6 PSA - Confidential 76/ 1 197565783010 4.60 19 a80 76/ 2 30076580 II 7a60 22 a90 7613 30056570 It 1a80 5 a20 78- 154 British Coal - Confidential 160 British Coal - confidential 162 c 3251983 678 5 .oo 51.OO 51 .00 163 British Coal - Confidential 165 32806559 166 32866565 167 33376535 168 33446666 1867 53.04 91.44' [Boreholes 168 and 13 may be the same] 169 33316674 1867 47.55 166.42: 170 33676678 1867 62.18 146.30+ 175 32406657 10.97 103.33+ 176 32916652 31a09 177 32106823 [? same boreho'le as 1781 178 32186825 126 a49' 180 30616820 91.44 181 30806827 41.15 182 30736827 57.61 183 30466523 3.35 196 30436911 1985 4 eo0 4.50 197 30446910 It 3 a80 4.50 198 30406907 II 3.50 5 .OO 199 33096754 1977 5.45 6.50 6 a50 11 200 ' 33066749 5 a30 6.50 6 a50 201 33136752 II 5.45 6.50 6 a50 202 33086748 11 5.30 6.50 6 -50 11 203 - 33116758 5.50 12.50 12.50 204 30096928 1983 4.98 4 a90 4 a90 205 30016935 It 4 e54 4.90 4.90 206 31686885 207 3153 6862 71.32+ 233 31256819 36 a58 243 31896757 16 a20 36.88 244 3% 6763 17.79 43 000 245 31966767 19 a70 42.00 246 31826753 16 a80 36.58 247 31976768 20.60 31.80 248 33606738 1978 c 4.90 11 .oo 11 .oo 249 33696735 II c 4.60 11 a00 11 .oo 250 33666735 Ii 3.103 a14 3.10 251 33676734 I1 3a31 3.50 3 a50 252 33346786 1973 18 a50 18-50 253 33246773 11 15.30 15 a30 254 33146758 II 15-30 15.30 255 33326763 II 15 .20 15.20 256 33346755 11 15.20 15.20 257 33526775 11 14.17 14a17 - 258 33526756 It 15 20 15a20 I30 Deeside (North Wales) Thematic Geological Mapping

BGS Gri d Date of ' Surface Dri ft Number Reference drilling -1eve1 thichess Depth 259 33516736 1973 15 a20 15 a20 260 32806750 1972 6a55 6a55 26 32996738 II 6 a55 6 a55 262 33076748 I8 6 a55 6 a55 263 33276735 I1 6.55 6.55 264 33076718 II 6 a10 6.10 265 32906733 II 18 a59 18.59 266 32716741 II 9.30 9 a30 267 32906724 11 9 045 9 a45 268 33106732 II 6 a55 6.55 269- 295 Bri ti sh Coal - Confi dential 296 33776742 1987 0 a48 55 .OO 55 a00 297 33676989 1986 4.75 12 a00 12.00 298 33716989 II 4.70 8aOO 8 a00 299 33696986 II 5 000 8 a00 8.00 I1 300 33646988 ' 4.85 8 a00 8 a00 301 33656991 II 4 a90 8.00 8 .OO

MAP SJ 36 SW 1 32796483 1862 c 45a70 25 a53 70 a61 2 33346463 II c 27.40 ?29 a51 97 a41 3 33936493 42 a01 42 a01 5 32306205 1899 57 a30 2 a82 52-88 6 32216175 11 57 a30 2 a06 32.92 8 c 32306225 1938 c 54a80 ?loa36 36 a58 9 c 32856220 1937 c 30-50 37 a80 10 3372 612'1 1947 46 a63 72 a54 11 33746136 1945 40 a84 106.55 12 33766134 1948 40.84 152.40 13 30696386 1972 113a34 3-10 12-31 14 30996368 11 126.27 Ni 1 18.00 11 15 . 3124 6361 120.93 Ni 1 13.00 16 32716315 II 43 a35 10 a10 10 010 17 33936309 II 22 a83 7.20 7a20 18 30606485 1979 13a50 13.80 19 32026454 II 7 -30 7a50 20 32836290 II 9 a20 9 a80 21 30386036 1982 117 a86 5 000 5 a00 22 30346045 II 116.49 5 a00 5 a00 23 30356049 II 117 a03 5 a00 5 a00 24 30286052 II 116 a72 5 a00 5 a00 25 30206059 II 113.55 5 a00 5 000 27 30056072 II 109 a99 5 a00 5 a00 28 30026200 It 107 a49 5 a00 5 a00 29 30086208 11 110 a59 1.30 3.80 30 30146216 II 112 a38 3.20 5 a00 31 3019 6224 11 113 a58 2 a90 4.75 33 30246233 II 114 a31 3 a50 4 a00 34 30296242 II 114 a43 2.50 5 a00 37 30066392 Ni 1 75 044 39 33406153 1939 c 29aOO 15.85 28.96 40 3307 6026 c 37aOO 0 a30 7 .OO 41 30336289 4 a57 Deeside (North Wales) Thematic Geological Mapping 131

BGS Gri d Date of Su rf ace Dri ft Engineering Number Reference drilling 1eve1 thickness Depth p ropert ies MAP SJ 37 SW

4 31997258 1938 c 4.57 17 e67 183 e 18 5 32937183 II c 4.88 16 e46 182 e88 7 33677124 II c 4e88 14 e48 174 e04 8 c 33167080 4 e57 ?155 e45 9/ 7 33467006 1971 4.57 3 e96 3 e96 9/8 33497015 I1 5 e15 3 e96 3 e96 9/ 9 33537024 11 4 e88 3.96 3 e96 9/10 33577034 II 4 e66 3e96 3 e96 9/ 13 33747073 11 4 e63 3 e96 3 e96 9/14 33787083 II 4.69 3.96 3 -96 9/ 15 33817092 II 4e88 3.96 3 e96 9/ 16 33857100 II 4 e88 3 e96 3e96 9/ 17 33887107 II 5.18 3 e96 3 e96 9/ 18 33837063 II 4 e66 3.96 3-96 9/ 19 33427043 II 4.66 3 e96 3 e96 9/ 21 33517067 I1 4e82 3.96 3e96 9/ 22 3347 7081 II 4.88 3.96 3 e96 9/61 c 33707065 11 5 e27 19.51 19 e51 9/ 62 II II 5 e18 20e12 20.12 9/B3 II II 5 e12 17 e37 17.37 9/ B4 II tl 4 e88 16 e76 16.76 9/B5 II II 4 e88 17 e22 17 e22 9/B6 33587071 It 4 .57 8.53 8-53 9/ 68 33707037 II 4 e88 6 .lo 6-10 9/B9 33747062 II 4 e97 12 e04 12e04 9/610 3379 7066 II 4 e94 9 e14 9.14 9/Bll 33807074 II 4 e57 9 e14 9.14 11 32027256 II 15 e39 183e49 12 33677124 1969 14 e32 185.01 13 CeEeGeB. - Confidential 14 3244 7150 1974 12.10 12.10 II 15 . 32087165 12.10 12.10 16 31797172 II 9.10 9.10 17 31457191 II 12 e10 12e10 18 32207114 II 12.10 12 e10 19 31697138 II 9.10 9.10 20 31287144 II 12.10 12.10 21 31777095 II 9 e10 9 e10 22 31817044 II 9 .lo 9 e10 23 32097018 II 9 e10 9 e10 24 30977211 1984 ?33.50 38 e 50 25 30977209 II ?35 e00 37 e50 26 31027210 11 34.00 39 e00 27 31047205 II 34 e00 38 e50 28 31097207 11 35 e50 39e50 29 31257205 11 34 e00 43 -50 30 30907208 II 36.50 41 e00 31 30827211 II 35 e00 40 .OO 32 30887205 II 40eOO 42.50 33 30727207 II 38 .OO 46 .50 II 34 30377134 1949 c 47.24 54 e86 I1 35 30467135 45.72 49.68 - 36 30407167 II c 42.67 45.72 132 Deeside (North Wales) Thematic Geological Mapping

APPENDIX D List of shafts sunk for coal

6GS British Gri d Drift -No . Coal No. Reference thickness Depth Coments MAP SJ 17 NE

59 16 19077799 150.88 122 17 122 1906 7796 ?36 -58 ?Adit 123 18 19077794 69.49 134 29 19617746 59.44 ?Posi ti on

MAP SI 26 NW

2 7 or 8 79.85 (See SJ26NW/97 and 98) 3 uncertain Site 4.11 57.30 4 14 2469 6563 2469 14 4 3.04 60 .42 (See SJ26NW/104) 91 1 24156594 Adi t 92 2 24126592 Adit 93 3 93 24146588 Adi t 94 4 94 24156586 7.01 95 5 24166582 Adi t 96 6 2412 6578 Adit 97 7 24896593 79.85 (Depth may apply to this or next shaft) 98 8 24906595 Capped 99 9 24946593 100 10 24996585 ?70.10 101 11 24986580 64.01 102 12 24476561 103 13 24506563 104 14 24696563 3 -04 60.42 Same as 26NW/4 105 15 2465 6557 106 16 24386541 67 .97 Capped 107 17 24406538 67.97 108 18 24416534 109 19 24506538 110 20 24536539 111 21 24486530 112 22 2446 6511 113 23 24516513 114 24 2460 6504 7.92 Borehole to 50.90 115 25 24926520 ?32 .OO 116 26 24886514 Adi t 117 27 2489 6514 Adi t 118 28 24896513 119 29 24896512 120 30 24866507 121 31 24946507 122 32 2337 6723 123 33 24926504 Deeside (North Wales) Thematic Geological Mapping 133

BGS Bri ti sh Gri d Dri ft -NO a Coal NO. Reference thi chess Depth Comments 124 34 124 2493 6501 125 35 24716623 126 36 126 24896501 127 37 24036842 128 38 24086837 13-72 129 2070 6766 130 20696764 131 20746758

MAP SJ 26 NE 1 45 or 46 c 27266757 11a88 135 a94 See 26NE/877 and878 2 British Coal - Confidential 5 162 5 26486501 85 a 34 Borehole to 122-22 7 85 2986 6608 ?303a58 8 124 8 ?28466535 147 a19 Capped 833 1 2669 6883 85.95 834 2 834 26686882 85 a 95 835 3 835 26906880 c 86.87 836 4 2688 6877 837 5 28476908 838 6 29326925 839 7 839 2978 6835 840 8 840 2999 6836 841 9 29896823 842 10 29886821 843 11 2990 6818 844 12 844 29716808 845 13 845 2972 6811 846 14 29736812 847 15 847 2977 6813 848 16 29816814 849 17 2984 6813 850 18 2988 6810 851 19 2994 6788 137 a46 (Depth may apply to this or nextshaft) 852 20 852 29956790 137 a46 853 21 2624 6797 Capped 854 22 2630 6806 Capped 855 23 855 26336805 25 a91 856 24 26566814 857 25 26546806 91a59 858 26 26766821 859 27 26746809 860 28 2685 6813 861 29 2685 6812 862 30 2694 6805 863 31 2704 6796 864 32 26566796 865 33 . 2659 6790 866 34 866 2638 6780 130 a58 Capped 867 35 26416781 101a41 Capped 868 36 868 2686 6787 1.52 870 38 2690 6787 134 Deeside (North Wales) Thematic Geological Mapping

BGS Bri ti sh Grid Dri ft -No. Coal No. Reference thickness Depth Comments 2687 6784 1.52 87 1 6784 39 2687 872 40 26686770 873 41 873 26726764 874 42 26976763 87 5 43 5 87 27026763 876 44 27046764 877 45 2727 6760 (Section for SJ26NE/l may apply to this or next shaft) 878 46 878 2726 6753 879 47 27466769 880 48 880 27746711 Adi t 881 49 27756713 Adit 882 50 27816717 Adi t 883 51 27876717 ?24 .38 884. 52 27816710 Adit . 885 53 885 27816708 Adit 886 54 2895 6753 2895 54 886 887 55 28946749 14.63 888 56 28986747 889 57 28906736 890 58 28846732 89 1 59 29036737 892 60 29056729 a93 61 6722 2897 8 94 62 894 29366720 895 63 895 29456702 896 64 896 2950 6693 897 65 897 26026696 8982607 66 6663 899 67 26316645 94.18 900 68 26336645 94 .18 901 69 26356633 902 70 27446625 305.41 903 71 27496625 317.60 904 72 904 27546624 168.86 Capped 905 73 905 28456633 19.80 Capped 906 74 906 28486631 88.30 5.00 907 75 28506627 Capped 908 76 28536627 909 77 909 28396614 21.64 910 78 28346607 911 79 28446607 912 80 912 29406640 913 81 29416635 914 82 914 29616612 915 83 29696613 916 84 916 2977 6613 917 29626829 Adi t 918 86 2651 6593 919 87 919 26476587 73.15 920 88 2645 6583 54.86 921 89 921 26596584 36.58 922 90 26666585 923 91 923 26556566 924 92 26526561 Deeside (North Wales) Thematic Geological Mapping I35

5GS British Gri d Dri ft -No. Coal No. Reference thicknessDepth Comnent s 925 93 26516557 926 94 26636563 927 95 26586548 928 96 2658 6547 929 97 2653 6539 930 98 26546537 931 99 26566534 22.86 932 100 26606536 99.06 Capped 933 101 26586523 Adi t 934 102 26636512 17.37 935 103 26966557 Adi t 936 104 27056561 25.60 937 105 27056559 Adi t 938 106 27226596 Adit 939 107 27286559 940 1oa 27296554 Capped 941 109 27466567 Capped 942 110 27536570 943 111 2765 6512 944 112 27686510 945 113 28276570 946 114 28286571 947 115 28366566 948 116 28376566 949 117 28426564 950 118 28446564 951 119 28436556 952 120 2855 6562 953 121 28586560 954 122 2829 6543 955 123 28276535 116.13 956 29446791 957 125 28456531 118.87 Capped 958 126 28786538 959 127 28806540 960 128 28596590 961 129 28576584 54 86 Capped 962 130 28626589 Capped 963 131 29376593 164.59 964 132 29396590 164.59 965 133 29216542 26.60 Capped 966 134 29176535 27.43 967 135 28986502 27 .43 968 136 29326531 969 137 29276527 46.80 970 138 2925 6508 54 0 86 971 139 29306509 45.72 972 140 29666565 8.84 973 141 29676563 13.11 974 142 29746559 ?82 .30 Capped 975 143 2979 6564 Capped 976 144 29856572 977 145 2964 6549 ?59.44 Capped 978 146 29696550 -_ 979 147 29746541 136 Deeside (North Wales) Thematic Geological Mapping

BGS Bri ti sh Gri d Dri ft -No. Coal No. Reference t hi ckness CommentsDepth

980 148 29646530 , 73.15 98 1 149 29736531 982 150 25436506 983 $51 25466508 984 152 26086657 985 153 26106656 986 154 26226646 987 155 26236615 988 156 26236610 989 157 26416601 990 158 26456595 99 1 159 26686584 992 160 26606558 993 -161 26516537 994 28946758 995 163 27056577 996 164 27296562 997 165 27316548 Capped 998 166 27406542 . 999 167 27456531 1000 168 27116522 1001 169 27136510 1002 170 27176515 1003 171 2726 6514 1004 172 27306506 1005 173 27376511 1006 174 27406511 1007 175 27386518 1008 176 28446585 Capped 1009 177 28506585 Capped 1010 178 28656614 ?Shaft 1011 179 28586649 1012 180 28616667 1013 181 29156636 1014 182 28356643 1015 183 29616679 54.86 1016 184 29636680 54.86 1017 185 29996640 1018 186 29996640 10 19 187 29066575 36 -58 1020 188 2946 6564 1021 189 29716560 1022 190 29766563 ?Same as SJ26NE/975 1023 191 29626549 59.44+ 1024 192 29756536 1025 193 29746534 32 .OO 1026 194 29486522 1027 195 29376515 49.20 1028 196 29156531 1029 197 29596520 1030 198 29656500 1031 199 25246568 ?91.44 1032 200 25096544

1033 201 2656 6529 Adi t -. 1034 202 2703 6570 Adit Deeside (North Wales) Thematic Geological Mapping 137

BGS Bri ti sh Gri d Dri ft -No , Coal No, Reference thickness Depth Comments 1035 29546808 1036 2956 6808 1037 205 2850 6609 1038 206 29646566 Adi t 1039 207 2965 6573 1040 208 29256617 1041 209 28756572 Capped 1042 210 2845 6606 Adi t 1043 211 2980 6573 1044 212 2980 6573 1045 29536806 1046 214 26526517 14.63 1047 215 26436590 1048 216 2709 6862 1049 217 25086547 1050 218 28426999 ?Same as SJ27SE/ll 1051 219 29016742 Adi t 1052 220 29006739 Adi t 1053 221 28946720 1054 222 27246600 1055 223 2849 6659 1056 224 28696662 1057 225 2980 6661 77.70 Capped 1058 226 29796660 55 000 Capped 1059 227 29086598 1060 228 28406597 1061 229 28266550 1062 230 28336565 1063 231 28216573 1064 232 2830 6566 1065 233 28206565 1066 234 2780 6715 ?Adi t 1067 235 27866690 Adi t 1068 236 27876687 1069 237 29716808 1070 2 38 27226544 1071 239 27206537 1072 240 27016521 1073 241 27276519 1074 242 27356530 1075 243 2606 6717 1076 244 27476550 1077 245 27516547 1078 246 29996624 1079 247 29236627 8 .OS 1080 2 48 29246623 1081 249 2952 6634 1082 250 2959 6628 1083 251 2955 E625 1084 252 2824 6600 1085 253 2822 6596 1086 254 28616595 1087 255 28486540 1088 256 28396520 1089 257 29886652 138 Deeside (North Wales) Thematic Geological Mapping

BGS British Gri d Dri ft -NO l Coal No, Reference thi ckness Depth Comments 1090 258 28636623 1091 259 29226560 1092 260 2940 6530 1093 261 29976842 1094 262 29846808 1095 263 29846796 1096 2 64 29866791 1097 265 2983 6790 1098 266 29996856 1099 267 29586671 1100 268 2925 6704 79 m25 1101 269 29286703 109.73 1102 270 29696635 1103 271 29836632 1104 272 29846626 1105 273 29816624 1106 274 2987 6622 1107 275 29816616 1108 276 29446598 1109 277 26086647 1110 278 26096679 1111 279 26106676 1112 280 26136664 1113 281 26196660 1114 28 2 26086662 1115 283 26086660 1116 284 25986671 1117 285 25996669 1118 286 25976667 1119 287 2600 6673 1120 288 26036672 1121 289 26286600 1122 290 29666531 1123 291 27366785 1124 292 27496998 1125 293 27496997 1126 294 27486995 1127 295 29166502 1128 296 29316501 1129- 297 - 1137 305 c 29486503 (Bell-pits, not individuallysited) 1138 306 1138 29206500 1139- 307-1139- 1143 311 1143 c 2950 6512 (Bell-pits, not individuallysited) 1144 312 1144 25036542 1145 313 1145 27066767 i146 314 i146 2680 6830 3.05 1147 31 5 114731 26136653 1148 316 1148 26146651 1149 317 26106651 1150 318 1150 26156649 1151 319 1151 26166648 1152 320 1152 26176647 Deeside (North Wales) Thematic Geological Mapping I39

BGS Bri ti sh Gri d Dri ft -No . Coal No. Reference thi chess Depth Comments 1153 321 26186614 1154 322 26146613 1155 323 26176612 1156 324 26206613 1157 325 27126790 1158 326 27086787 1159 327 1160 328 1161 329 1162 330 1163 331 28416632 19.50 Capped 1164 332 28576620 Capped 1165 333 29576639 23.50 Capped 1166 334 29586642 25 .OO Capped 1167 335 29546639 26 .OO Capped 1168 336 2924 6539 Capped 1169 337 29326520 Capped 1196 29116574 1197 29446603 1198 2992 6829 1199 25486717 ? Shaft 1200 26276635 ?Shaft 1201 26926806 1314 29346782 ?Shaft 1315 28916754 ? Shaft

MAP SJ 26 SW 1 11 2449 6464 11.28 85 a95 4A 23 24226328 222.81 ?13.79 48 24 24176331 192.02 5 48 2430 6375 132.54 6 42 24216145 9.25 49 .37 7A 27 23826284 13.96 201.78 78 26 23796286 ?4 .57 ?133.50 Drilled to 150.00 7c 25 23836288 146A 1 2377 6450 100.58 Capped 146B 2 23746454 85.95 Capped 147A 13 24706412 137 -16 Capped 1478 14 24726409 137.16 . Capped 148A 37 24346205 ?42.67 148B 38 24346203 149 43 23746023 222 .50 183A 31 23786220 93.27 1838 33 23986227 82 .30 184 20 23596335 19.81 ?132.59 185 22 23896332 68.58 ?Drilled to 153.82 208 53 2435 6271 272 10 24546466 72 .24 273 3 24906496 274 4 24916483 275 5 24806468 46.63 276 6 24826464 31.09 277 7 24836463 16 -46 140 Deeside (North Wales) Thematic Geological Mapping

BGS Bri ti sh Gri d Dri ft -NO a Coal NO. Reference thickness Depth Comments 278 46 8 6463 2479 a63 279 ?66 9 6461 2474 a75 280 12 24866437 281 15 24926406 28 2 16 24946404 283A 17 23906412 28.96 283B 18 23926411 284 28 24136285 285 29 24136258 286 30 23716224 111 a56 Capped 288 32 23906224 ?91 a44 289 34 24056227 73.15 290 35 24086226 54.86 291 36 24416217 12 a80 292 39 23466150 ?82m30 or 171.13 293 40 2348 6150 ? I71 a 13 or 82 a30 294 41 24206150 295 44 23776023 122 a07 296 45 24346011 c 176.48 297. 46 24246004 Adi t 298 47 24246002 Adi t 299 19 24356372 ?Capped 300 49 24236373 14.63 - 301 50 23936375 45.72 302 51 24196358 304 52 24416135 9.14 9.14 305 54 24486292 59 a44 306 55 2427 6267 45.72 307 56 24286272 308 57 2439 6381 21 95 309 58 24216333 310 59 2420 6228 311 60 24306247 45 a72 312 61 24386238 14.63 313 62 24406239 14.63 314 63 24396236 315 64 24286230 79 e55 320 21 23636335 129 a84 321 65 23786218 322 66 24666292 ? Shaft 323 67 24366258 ?Shaft 324 68 24296257 ?36 a58 ?Shaft

MAP SJ 26 SE 3 13 25076344 15.24 164 a59 Capped 4 100 29356400 132.59' Capped 6 102 6 29516395 121a61 7 33 27246384 15 a84 87.17 Capped 8 48 28296428 6.62 195 a88 Capped 11 120 27216286 26 a67 52.73 12 36 27246359 5 a48 31.69 Deeside (North Wales) Thematic Geological Mapping I41

BGS British Gri d Drift -No. Coal No. Reference thickness Depth Comnent s 13 ?121 (See BGS No. 600 ) 14 162 14 2766 6143 169.67 15 118 29266244 (Adjacent to S326SE/586 . Depth 110.94 may be either shaft) 17R 26496456 14.60 Drilled to 17,OO 22 108 29406365 67.05 Capped.Dri 11 ed to 69.00 490 163 2772 6145 4 e57 144 -48 586 119 29246244 See SJ26SE/15 587 233 29386244 45.72' 588 29336243 ?Shaft 589 117 29376273 590 169 28076146 591 170 2814 6140 592 171 2800 6131 18 .29 593 172 2804 6114 594 124 28076246 ?36.58 595 2829 6288 36.58 596 28566884 54.86 597 28306286 598 173 28106103 599 174 28116102 600 121 27236242 10.97 27 e43 601 123 27776246 ?13.72 ? 602 122 27776250 607 26916393 ?Shaft 610 2643. 6449 ?Shaft 611 247 26056030 612 248 25906024 613 249 2602 6023 614 250 25916003 618 125 25556183 89.92 Capped 619 126 25556180 36.58 Capped 620 127 2561 6180 621 212 25546190 622 18 2539 6283 79.55 623 17 25356292 624 2544 6271 625 25506278 626 25326285 91.44 627 16 25336307 628 14 25086341 82.30 Capped 629 15 25116334 ?Shaft 630 8 25016377 64.01 Capped 631 9 25096374 64.01 632 10 25196376 639 115 2947 6298 Adi t 640 116 29466297 Adit 641 218 2941 6296 18.29' 642 226 29516296 13.11 643 230 29596297 8.53 740 2 38 26536005 741 251 26206070 142 Deeside (North Wales) Thematic Geological Mapping

BGS British Gri d Drift -No . Coal Nom Reference thicknessDepth Comments 742 187 742 6067 2636 23.77' 743 188 743 26366064 744 26376071 745 189 745 26466064 ?77.72+ 746 190 26266055 16m15+ 747 191 26286056 10.06 748 252 748 2638 6055 749 192 749 26296041 15.54 750 193 750 26316041 45.42 751 194 751 26436039 78.64 Capped 752 195 752 26506042 753 26546041 c 18.29 (?Same shaft as No. 752) 7 54 243 2672- 6051 755 282 26966006 756 152 26556102 ?54.86 757 153 2659 6101 ?54 m86 758 154 26656098 759 155 26806093 82.30 Capped 760 156 2681 6093 ?82.30 Capped 76 1 157 2691 6097 762 158 27016700 Adi t 764 26546092 ?25 .60 768 244 26806062 Adi t 769 159 2715 6100 51 m21' 770 286 27056096 771 287 27186075 772 27106094 773 198 27126027 23 m77f 774 199 27146029 28 .35' 775 196 2702 6007 24.99 776 197 2702 6005 Adi t 777 2 39 2727 6010 778 240 27226009 779 27326013 780 201 27396014 1 781 200 2742 6029 782 202 2753 6027 Capped 783 203 27506036 Adit 7 84 204 27516035 28.35 Capped 785 205 27526034 Adi t 786 206 27526055 Adi t 787 207 27526051 ' 18.29' 788 208 27586044 789 209 27586042 Adi t 790 225 2783 6045 36.58' 791 210 2795 6050 Adi t 792 211 27966047 794 - 175 27846088 795 176 27876085 796 177 27946085 797 178 27726084 27.131 27736081 27 .13+ 798 179 -_ 799 180 27746079 9 m14 800 185 27806070 ?Borehole Deeside (North Wales) Thematic Geological Mapping 143

BGS British Gri d Dri ft -No . Coal No. Reference thicknessComentDepth s 801 186 27936070 802 168 27596095 27.43' 803 181 27596079 71.32 804 182 27616076 80 5 183 27646078 65.43 806 184 27666066 36.58 811 11 25826373 812 12 25846375 813 219 25886370 814 1 2515 6499 27.74 815 2 25026432 91.44 816 3 25096413 9.14' 817 4 25266412 Capped 8 18 5 25256411 Capped 819 6 2577 6401 820 7 25876404 821 25166484 822 25016401 823 25016396 824 2507 6402 825 25086400 826 25266414 828 160 27316137 829 161 27366143 830 164 2753 6130 64.01' 831 165 27516127 ?Same as No. 830 832 166 27526113 ?31.09 833 167 27716106 160.02 834 27576107 837 128 2683 6142 32 .OO 838 246 26606126 Adi t 8 39 144 2665 6123 14.63 840 145 26706124 ?82.30 Capped 841 146 26726120 Adi t 84 2 147 26796116 Adi t 843 148 26846115 Adit 844 149 26886112 845 150 2691 6110 Adi t 846 228 26926110 Adit . ?Same as No. 845 847 151 26946106 Adi -t 848 129 27016147 Adit 84 9 130 27006145 Adi t 850 131 27026141 Adi t 851 132 27006139 Adi t 852 133 26996137 7.32 853 134 26926131 Adi t 854 135 26946130 Adit 855 136 26826135 85 6 137 2683 6134 Adit 857 138 26846124 Adit 858 139 2689 6127 Adi t 859 140 26896127 Adit 860 26616152 86 1 2675 6134 862 26856130 144 Deeside (North Wales) Thematic Geological Mapping

BGS BriGri ti sh d Dri ft -No . Coal No. Reference thickness Depth Comments 865 141 26926124 Adi t 866 142 26936123 Adi t 867 143 867 26946120 Adi t 868 229 26906123 Adit 869 227 26976127 Adi t 870 113 870 29646315 87 1 114 29576306 872 231 872 29576320 873 29596342 73.15 (Depth may refer to this or next shaft) 874 29606344 73.15 875 236 875 29606316 876 232 876 29256332 877 29206301 36.58 (Depth may refer to this or next shaft) 878 29206300 36.58 87 9 2953 6307 880 29536305 881 111 (253)29546345 ?73.15 882 29436311 8 .23 883 29346331

' 884 29186351 887 112 29426340 12.19 888 110 29426350 Adit 889 107 29356366 890 109 29526368 891 101 29266391 89.61 Capped 892 103 29586395 77.72 .. 893 104 29596394 64.01 895 69 29016397 104.24' 896 70 29026400 Capped 897 71 2915 6393 ?73.15 898 52 28316345 899 53 28386328 900 54 28546331 901 55 28576320 902 56 28636337 903 57 28676344 Capped 905 59 2865 6354 906 60 28746356 109.73 Capped 907 61 2875 6360 Capped 908 62 28846362 909 63 28866350 910 64 28866350 911 65 28636408 912 66 28666403 196 .20 913 67 28906401 914 68 28936399 27.43' 915 49 . 2835 6382 100.58' 916 50 2834 6380 917 51 2823 6371 9 18 105 28956377 9 19 106 28926371 920 217 2880 6334 9 21 279 2820 6350 Deeside (North Wales) Thematic Geological Mapping I45

BGS Bri ti sh Gri d Dri ft -No . Coal No. Reference thickness Depth Comments 922 2887 6331 923 32 27216383 18.29 Capped 924 34 2730 6383 925 35 27326384 926 37 27246354 Adi t 927 38 27426392 928 39 27486381 Capped 929 42 27786384 19.80 Capped 9 30 43 27706371 931 44 27716321 152.70+ 932 45 27706309 60.96 933 46 27706305 934 220 2755 6367 935 221 2763 6366 936 222 27696366 937 223 27716356 938 224 27576341 939 27716363 940 234 27646348 941 271 27486334 942 272 27466326 943 273 2746 6335 944 274 27456334 945 275 27436329 946 275 27466330 947 27436345 948 27036467 106 .98+ 949 2705 6469 97.84+ 950 27106479 73 .15+ 951 27146483 69.49+ 952 27306496 46.03 953 27596470 954 27466464 17 .OO 955 2739 6439 141.73' 956 27386436 Adi t 957 2725 6424 958 27266419 44 .20 Capped 959 2717 6413 960 27456421 961 27716412 Capped 962 27796411 Capped 963 27126480 ?69.49 964 27366444 965 27186423 966 28306429 196.90 Capped 967 2883 6486 968 28886497 208.48" 969 28916499 c 208.48 970 2894 6476 97 1 28986469 ?129.84 972 28926462 973 28976458 974 2915 6490 -_ 975 29196492 976 2911 6466 Capped 146 Deeside (North Wales) Thematic Geological Mapping

BGS Bri ti sh Gri d Drift -NO a Coal NO, Reference thi chess Depth Cments 977 82 ?1292910 6462 a84 978 96 29196434 979 97 29126424 980 98 29156417 Capped 981 99 29406426 98 2 83 29216458 983 29236459 984 84 29136476 54.86' 985 85 (237) 29366467 986 86 29406462 30aOO 987 a7 29376450 988 213 29396449 989 214 29416449 990 241 2927 6449 991 280 2933 6454 18 a 29+ 992 88 29536468 77 a72+ 993 89 29576496 74 a98 994 91 2957 6466 77.72' 995 92 2967 6461 20.12 996 93 29686459 6.40 997 94 2970 6461 998 95 29706460 999 270 2930 6483 1000 ?642776 6436 a01 ?Borehole 1001 254-269 (Closely adjacentbell -pits, not individually sited) 1002 6485 2906 1003 2916 6487 2916 1003 1004 ?45 2946 6483 a72 1005 2961 6463 2961 1005 2941 6478 54.86 10066478 2941 1007 2768 6335 2768 1007 10082843 242 6331 1009 2935 6485 9.14 6485 2935 1009 1010 6360 2960 1088 278 ?2925 278 1088 25.60 6160 I 1089 28 1 12a19 Capped 1090 283 1090 1091 284 1092 285 1093 288 14.60 1094 289

MAP .SJ 27 NW

2 5 21587603 a37 25 394 a11 69 1 2105 7588 70 2 21367595 71 3 2137 7594 269.75 72 4 2i40 7590 74 6 21567598 388 a 16 Capped 75 7 75 21347578 256 a03 __ 76 8 2127 7574 77 9 77 21297560 63 a09 Deeside (North Wales) Thematic Geological Mapping 147

BGS Bri ti sh Gri d Dri ft -No. Coal No. Reference thickness Depth Comnent s 78 10 21327551 ?292.60 79 11 21377549 80 12 21237542 81 13 2131 7540 82 14 21367543 83 15 21387540 84 16 21367538 85 17 2140 7531 86 18 21377523 87 19 21317519 ?64.01 88 20 20927507 Adi t 89 21 20897505 90 22 21427545 91 23 21457545 ?159.10 Capped 92 24 21497542 93 25 21477537 94 26 2154 7540 95 27 2157 7542 96 28 2158 7551 97 29 21617562 98 30 2151 7595 269.70 99 31 21647558 ?146.90 100 32 21687560 ?147.04 101 33 21657548 102 34 2166 7543 103 35 21787552 104 36 21817550 105 37 21737531 106 38 21797523 107 39 21787515 Capped 108 40 21847512 51.80 109 41 21977522 110 42 2198 7515 ?I .80 ? Shaft 111 43 21287543 112 44 2143 7574 ?Same as No. 139 113 45 2116 7563 114 46 21367578 ?Same as No. 75 115 47 21547550 116 48 2177 7518 117 49 2181 -7518 118 50 - 21687564 119 51 21847552 120 52 22157521 121 53 22207517 122 54 21087618 82.30 123 55 21147614 124 56 21317619 ?Shaft 125 57 21387612 ?Shaft 126 58 21467617 ?Shaft 127 59 2135 7596 128 60 21397952 129 61 21727561 130 62 21037456 Adi t 131 63 20887640 -_ 132 64 2089 7633 27.40 148 Deeside (North Wales) Thematic Geological Mapping

BGS Bri tish Gri d Drift -No . Coal No. Reference t hi chess Depth Comments 133 65 133 7617 2106 82.30 134 66 134 21437552 135 67 135 21657559 136 68 136 21687561 137 69 137 21907589 138 20947508 139 21457576 ?Same as No. 112 141 21047638 142 2106 7636 143 21637555

MAP SJ 27 SW

4 36 23527321 201.52 5 34 23287323 ?110 moo 279 23207336 ?70 .OO 28 2 55 23617322 343 35 23297313 246.89 Capped 344 24 22717320 45.72 345 57 23617318 346 37 24137343 354 21 23267426 Drilled to 156.20 356 22 23297423 Drilled to 189.00 358 1 21587482 359 2 21737488 360 3 22007469 36 1 4 22007466 362 5 22207479 128.02 363 6 22227470 95 010 364 7 22387478 365 8 22487471 366 9 22477469 ?128.63 Capped 367 10 22487467 ?128.63 368 11 22107452 97.84 ?Same as No. 369 369 12 22137452 ?Same as No, 368 370 13 22237447 371 14 22077442 ?Same as No, 372 372 15 22097443 ?Same as No. 371 373 16 22107430 374 17 22507443 375 18 22457438 376 19 2262 7426 377 20 22597422 378 23 21897400 7.62 379A 25 22677295 3798 26 22677292 379c 27 22727300 379D 28 22747302 379E 29 22777300 Capped 379F 30 22837300 379G 22787297 379H 22777295 380 31 22907306 381 32 23017303 Deeside (North Wales) Thematic Geological Mapping 149

BGS Bri ti sh Gri d Dri ft -No . Coal No. Reference thi chess Depth Comnent s 382 33 2287 7384 383 38 24247345 384 39 24267344 246 .89 385 40 24137337 386 41 24337333 387 42 24157328 388 43 24087316 389 44 24187290 114.30 390 45 24097266 117.04 39 1 46 24047261 392 47 23967249 112 000 393 48 24207239 130.15 394 49 23867230 395 50 2385 7226 396 51 24647242 ?18 28 397 52 24797240 ?18.28 398 53 24127164 149.96 399 54 24927169 ?54.86 400 56 24107268 100.58 401 58 23897212 402 59 23957265 403 60 24297271 404 61 2474 7236 c 15.24 405 62 22767265 406 63 22077422 407 64 21767442 408 65 22507443 Same as No, 374 409 66 24247227 6.71 Capped 410 67 411 68 24177288 421 22117305 422 2075 7436 Adi t 423 21917405 3 -05 426 21297260 427 2116 7216 428 21357219 429 21407219 430 21447220 431 2197 7199 432 22127189 433 22147187 434 2243 7100 438 22077194 439 22107194 440 22907120 Adi t 442 22907223

MAP SJ 27 SE 179 2 26677142 ?54 .86 180 3 26217141 181 4 26227119 182 5 26257105 183 6 26217088 150 Deeside (North Wales) Thematic Geological Mapping

BGS Bri ti sh Gri d Drift -No. Coal No. Reference thickness Depth Comnent s 184 7 25927027 185 8 2587 7025 186 9 25917024 187 10 28397010 188 11 2845 7000 30.48 Drilled to 31.09. Capped 189 12 27537008 190 13 27537004 19 1 14 27537002 192 15 26697139 193 16 26177117 194 17 26187124 195 18 26217123 196 19 26247121 197 20 26217095 198 21 26227094 199 22 26207092 200 23 26227092 201 24 26297089 202 25 26327090 203 26 26307087 204 27 26327088 20 5 28 26287084 206 29 26287082 207 30 26207090 208 31 25927023 209 32 26817105 Adi t 210 33 248 26197119 249 26287095 250 26307086 251 27517003

MAP SJ 36 NW 16 1 31286846?24 082 88.06 Capped 17 2 3113 6845 ?12 -80 92.91 18 3 26.316770 3181 153.62 19 6 67403165 7.95 161.09 41 32 65663323 39.62 145.47 77 7 31926720 ?10 .O6 94 .O6 171 23 32406614 172 38 32016636 173 21 32056647 8.53 ?94.18 m deep 174 22 32056644 66 .OO+ ?94 -18 m deep. Capped 179 50 31676636 7.62 184 24 30046570 Capped 185 25 3005 6569 Capped 186 26 30306563 Capped 187 27 30466567 Capped 188 28 30586570 Capped 189 29 30676571 Capped 190 49 30696571 191 39 30836565 Deeside (North Wales) Thematic Geological Mapping 151

BGS Briti sh Gri d Dri ft -No. Coal No. Reference thickness Desth Comments 192 30 3084 6564 193 31 30876563 194 30886562 ?Shaft 195 30916560 Adit 208 4 31786774 156.36 20 9 ?5 31666741 91.49 210 36 31676739 211 33 31726764 36.58' 212 34 31656760 82.30' 213 35 3165 6758 54.86 214 8 31856715 215 9 31296699 95.10: Capped 216 10 3135 6697 92.35 Capped 217 47 31846728 218 48 3182 6727 220 40 31176748 221 46 31886702 222 11 31706696 223 37 31716695 224 12 31846689 30.33 225 13 3183 6688 30.33

* 226 14 31786681 34.75 227 17 3175 6676 30.33+ 228 15 31706682 15.24+ 2 29 16 31726681 18.90 230 18 31826674 36.58 231 19 31816672 34.14 2 32 20 31786670 25.60 234 31326813 235 41 31206807 236 31246801 237 31266797 238 45 3142 6805 239 31396799 240 44 31436800 241 42 31226807 242 43 31236802

MAP SJ 36 SW 30126485 19.20 Bored deeper 152 Deeside (North Wales) Thematic Geological Mapping

APPENDIX E

List sf shafts and adits identified as being open at surface, at the time of survey (1985-87) (All sites are shafts unless atherwise stated).

Comments N.B. These aresubjective assessments made SJ 17567634 atthe time of survey; fencing/capping may havechanged subsequently. 17657622

17217574

17047568

1721 7567

17247566

1741 7560

17307553

17397543

17947559

1793 7545

1809 7542

18537542

18787517

17677526 Surrounded by double wire fence; beside golf course

17377482 Inadequate capping; wire fence surround; on golfcourse

1771 7437 Surrounded by doublewire fence; actively collapsing . 1877 7367 Wi refence surround; on common land 1871 7354 Inadequatecapping; on cornonland

1863 7359 Inadequatecapping; wire fence surround; on common land

7345 Open?;1841 7345 shaft ledstone-wal __ Deeside (North Wales) Thematic Geological Mapping I53

19157334 Surrounded by double wire fence;actively collapsing

19107316 Surrounded by doublewire fence;actively collapsing

19387306

18717294 Deep; very poorly fenced off; on common land

1876 7297

18837296 High wire fencesurround; on comon land

18227238

18207237

19287199 Stone-wall ed shaft; on comnon land

1925 7164 Covered with rustingcar door; adjacent to footpath on common 1 and 1943 7154 Wire fencesurround; actively collapsing; on comon land 1564 6993

18656918 Wire fencesurround

18936927 Covered with sheet of corrugatediron 20026965 On common land

1999 6918 Poorly fenced off; on common land

2075 6939 Wire fencesurround; on common land

21036929 Wire fencesurround; on common land

21206925 On comnon land

19416886 Poorly fenced off

19606884 ?Open

1867 6888 Wi re fence surround 19076870 Wire fence surround

19526886 ?Open

. 1930 6776 Overgrown

20696764 Adit; partlysealed

2070 6766 Wire fencesurround

2181 6700 Deep 154 Deeside (North Wales) Thematic Geological Mapping

2005 6687 Acti vely coll apsi ng

20106682 to 20226688 Several shafts

19676743 Deep coI1 apse structure

19666724

19126736

19096732

19066710 to 19326712 Several shafts

18776653

1874 6644

19006646 to 19126645 Several shafts

18906632 to 19286641 Several shafts

18986560 to 19126562 Several shafts

20556507 Flooded at depth

20116488

18956448

18936444

19596465

19676468

19746402 Several shafts

19106364 1905 6363 Two adits 1978 6310 to 19986299 Several shafts

21566228

22116242

21786126

22006099

21016088

2086 6067 Deeside (North Wales) Thematic Geological Mapping 155

APPENDIX F Logs of boreholes sunk as part of the project to prove sand and gravel resources, with deri ved partide size data

Numbers arethose of the BGS 1:lO 000 record system Figures preceded by + arelevels in metres aboveOrdnance Datum

SJ 17 NE/67- 1995 7649 BagilltFarm Hall Surface 'level c + 56 Thi ckness Depth (m 1 (m 1 TOPSOIL/SLOPE WASH 0.30 0.30 TILL (BOULDER CLAY) Variegated, greenish ye1 7 ow to orange-brown fi rm si lty clay with abundant pebbles and cobb'les of sandstone, sandy in places; gradual co7ourchange at base SPT at 3.0-3.5 rn (64 bl ows) 3.70 4 .oo COAL MEASURES (Weathered) Dark bluish grey stiff silty clay with abundant fragments of darkmudstone and shale 1.oo 5.00

SJ 17 SE/103 1778 7453 Brynford Surfacelevel c + 226 MADE GROUND

Ti pped rubbi sh, stones ashes et c 0.80 0 -80 HEAD

Yellow-grey silty clay with numerous fragments of 1 i mestone and chert 3 -10 3.90 CEFN MAWR LIMESTONE Fragments of limestone (no penetration)

SJ 27 iw/a 2070 7557 Tyn-Twll Fam

Surface 1eve1 c + 67

TOPSOIL 0.30 0.30 156 Deeside (North Wales) Thematic Geological Mapping

Thickness Depth (m 1 (m 1 TILL (BOULDER CLAY) Darkbrown to reddish brown and ye1 1 ow sandy, si lty, poorly sorted fi rm clays with scattered pebbles and fragments of sandstones,coals etc 6 .20 6 -50 SPT at 3.0-3.5 m (15 bl ows) 4.5-5.0 m (9 bl ows) passes down into Gravelly sandy clay with occasional large boulders 2.80 9.30 SPT at 7.5-8.0 m (24 bl ows) Bluish grey clay with quartz pebbles and sandstone fragments gradationally passing down into SPT at 10.3-10.8 m (67 bl ows) 2.10 11.40 COAL MEASURES (Meat hered) Bluish greypebbly clay with abundant darkgrey mudst one fragments 0.60 12 .oo

SJ 27 SW/246A Fferm73612163 No 1 Surfacelevel c + 108 TOPSOIL 0.30 0 -30 ?HEAD Darkbrown to yellowish grey mottled silty clay with occasional pebbl es 0 -30 0.60 TILL (BOULDER CLAY)

Dark reddish brown and orange-ye1 low fi rm silty clay with abundantrounded pebbles and cobbl es of sandstone and coal fragments 5.60 6.20 Dark grey to brown gravel ly clay with occasi onal lenses of gravelly sands and silty sands (0.2-0.3 m thick) 1.60 7.80 SPT at 7.3-7.5 m (50 blows) Borehol e termi nated at obst ructi on

1 SJ 27 SW/246B 2163 7361 Fferm No 2 Borehol e resited 1 rn SW of SJ 27 SW/246A Surfacelevel c + 108

TOPSOIL . 0.30 0.30 ?HEAD Darkbrown si lty clay with occasi onalpebbl es 0 020 0.50

-_ Deeside (North Wales) Thematic Geological Mapping I57

Thickness Depth (m 1 (m z TILL (BOULDER CLAY) Dark reddish brown to ye11 owish green variegated silty andsandy fi rm clay with abundantpebbles and cobbles of sandstones , i gneous and metamorphi c 7 itho1 ogi es 6.30 6 .8O Coarsegravel, poorly sorted, with occasionalpockets ofclayey sand passing down into fine gravel 0 090 7.70 passing down into COAL MEASURES (Weathered) Dark grey silty clay with fragmentsof dark grey mudstone 0.50 8 -20

S3 27 SW/247 23777105 Pl as-y-Mynydd Surfacelevel c + 67 TOPSOIL

Pal e brown sandyclay with roots 0.25 0.25 TILL (BOULDER CLAY) <- Dark reddish brown to yellowish green variegatedsandy clay with pebbles and abundantsandstone fragments 1.15 1.40 Grey and brown gravellyto sandy clay;large cobbles up to 10 an, occasional thin lenses ofsand 4.25 5.40 SPT at 1.5-2.0 m (19 bl ows) 4.5-5.0 m (24 bl ows)

GLACIAL SAND AND GRAVEL Clayey to very clayey sand, medi urn brown to brown, with gravel lenses and thin beds oflaminated fine sand with organictraces 2.55 7 095 Cleandark brown sand with peatytraces I .05 9 000 Clayeysand with gravellylenses 1.80 10 A0 SPT at 6.5- 7.0 m (17blows) 8.0- 8.5 m (23blows) 9.5-10.0 m (28blows) Clayey to veryclayey fine to coarse sands, medi urn brown; bedding defined by thin peatylaminae and streaks 5 020 16 -00 SPT at 11.0-11.5 rn (25blows) 12.5-13.0 m (31blows) . 14.0-14.5 m (45blows) 15.5-16.0 m (32 bl ows) Clayey to very clayeyfine to coarsesand as above, but with numerousclay sandy beds 9 000 25.00 SPT at 17 .O-17.5 m (31 bl ows) 18.5-19.0 m (30blows) 20.0-20.5 m (51blows) 21.5-22.0 m (30 blows) 158 Deeside (North Wales) Thematic Geological Mapping

Parti cl e si ze analysis results

Mean for deposit Depth Percentages percentages bel ow surface (m) Fines Sand Gravel Fines Sand Gravel

4/16 +1/16 +1/4 +I +4 +16 +64 mrn -114 -1 -16 -4 -64 a 20 74 6 5*5- 6,5 21 17 42 5 7 80 6.5- 7.5 22 14 61 3 0 00 7.5- 8.5 20 25 47 5 2 10 8.5- 9.5 21 29 48 2 0 00 9.5-10 .O 15 9 42 14 13 70 Mean 20 20 49 5 3 30 b 20 80 0 18 11 61 10 0 00 20 11 58 9 2 00 25 21 53 1 0 00

26 b 36 38 0 0 00 18 34 47 1 0 00 11 33 56 0 0 00 20 24 52 4 0 00 a+ b 20 77 3 Mean 20 22 51 4 2 10. Deeside (North Wales) Thematic Geological Mapping 159

Thickness Depth (m 1 (m> SJ 27 SW/248 22677312 Apri 1 Rise Farm Surface level + 84 ?MADE GROUND Dark brown to orange-brownclay, ? disturbed 0.40 0.40 TILL (BOULDERCLAY)

Dark orange and brown clay with abundantpebbles andfragments of sandstone,coaly streaks 2.60 3 .OO Pal e ye1 1 ow and brown sandy clay with occasional gravel ly 1 enses 2.50 5.50 SPT 2.0- 2.5 m (13 blows) 4.5- 5.0 m (51blows) GLACIALSAND AND GRAVEL a Darkbrown quartzosesand, clayey in places with gravel lenses and scatteredpebbles 2 010 7.60 We1 1 -sorted, bedded, ye1 1 ow-brown sand 2.20 9.80 SPT at 6.5- 7.0 m (45 blows) 8.0- 8.5 m (36 blows) 9.5-10.0 m (49 bl ows) b Darkbrown clayeyand sandy gravel , dense in 1ower part 6.90 16.70 SPT at 11.0-11.5 m (121blows) 12.5-13.0 m (99 bl ows) 14.0-14.5 m (76blows) c Fine, well-sortedsand passes down intoclayey sand (0.3 m at 17.5 m) , passes down to ye71 owish brown medium-finegrained sand with thin clay beds 6.30 23 .OO SPT at 17.0-17.5 m (62 blows) 18.5-19.0 m (69 blows) 20.5-21.0 m (40 blows)

?LACUSTRINEDEPOSITS

Laminated reddi sh brown andye1 1 owish brown sandy and si 1ty c1 ays passing down into greyi sh brown laminated clay. Laminae defined by thin pale sandybeds up to 0.5 cm thick, occasionalsmall pebbles and possi bly she1 7 f ragments 2 000 25 .OO 160 Deeside (North Wales) Thematic Geological Mapping

Parti cl e size analysis results

Mean for deposit Depth Percentages percentages bel ow surface (m) Fines Sand Gravel Fines Sand Gravel

01/16+1/16 +1/4 +I +4 +16+64 IIIJI -1/4 -1 -64-16 -4

a 12 81 7 5.5- 6.0 10 10 39 19 12 10 0 7.5- 8.0 13 18 51 8 6 4 0 8.0- 8.5 13 31 54 2 0 0 0 9.0- .9.5 10 23 63 3 1 0 0 9.5-10 .O 12 31 47 5 3 2 0 Mean 12 23 51 7 4 3 0 b 748 45 10 3-11. 0 9 20 24 12 25 10 0 11.0-11.5 10 8 17 14 29 22 0 12.0-12.5 9 8 27 15 28 13 0 13.5-14 -0 11 7 18 16 35 13 0 15.0-16.0 1 1 17 26 31 24 0 Mean 7 7 20 18 30 18 0

C 11 89 0 17.0-17.5 9 62 28 1 0 0 0 18 -5-19.O 12 60 28 0 0 0 0 19 5-20 .O 4 25 67 2 1 1 0 20.5-21 .O 15 51 34 0 0 0 0 21.0-21 05 14 65 21 0 0 .O 0 22.0-22.5 15 82 3 0 0 0 0 Mean 11 58 30 1 0 0 0 a+ b+ 10 71 C 10 19 Mean 10 30 32 9 12 7 0 J Deeside (North Wales) Thematic Geological Mapping 161

SJ 27 SW/249 2495 7057 Troes -y-Mynydd Surfacelevel c + 69 HEAD

Darkbrown silty clay 0.30 0.30 TILL (BOULDER CLAY) Dark reddish brown clayey sands and stiff silty clay with abundant pebbles and cobbles 5.10 5 010 SPT at 3.0-3.5 m (34 blows) 5.0-5.5 m (63 blows)

GLACIAL SAND AND GRAVEL

Dark reddish brown clayey sand passing down into well -sorted clean orange to reddish brownsand 4.10 9.50 SPT at 6.5- 7.0 m (81 blows) 8.0- 8.5 m (74 blows) TILL (BOULDERCLAY) <- Darksbrown very clayey sand and gravelpassing down rapidly into firm stony clay 1.70 11.20 Borehol e terminated at obstruction SPT at 9.5-10.0 (71 blows) 11.0 (fai 1ed)

Parti cl e si ze analysis

Mean depositfor Depth 1 Percentages percentages I bel ow surface (m) Fines Sand Gravel Fines Sand Gravel I I 01/16+1/16 +1/4 +l +4 +16 +64 mm -114 -1 -4 -16 -64

14 86 0 5.5-6 .O ‘20 64 14 I1 0 0 6.5-7 .O 11 69 20 00 0 0 7 -0-7.5 13 49 38 00 0 0 8.0-8.5 1319 68 00 0 0 8 05-9 .o 10 65 25 00 0 0 Mean 14 63 23 00 0 0

-_ 162 Deeside (North Wales) Thematic Geological Mapping

Thi ckness Depth (m 1 (m) SJ 27 SW250 2169 7060 Penf ro Surface 1 evel c + 183 HEAD

.. .. Top soi 1 and thi n clayey wash 0.40 0.40 TILL (BOULDER CLAY) Firmye1 1 ow to greyish brown clay with coal and dark shalefragments, sandy inplaces 1.80 2 020 HALKYN FORMATION (Weathered)

Li ght grey rnudst one 1.00 3.20

SJ 27 SW/251 2073 7235 Pistyll Farm No 1 Surface 1 evel c + 167

TOPSOIL 0 030 0.30

1 HEAD

Li ght brown to ye1 1 ow-brown sandy cl ay with pebbl es 0.60 0 .go TILL (BOULDER CLAY) Reddish brown stony clay with Coal Measures mudstone pebbles 1.50 2.40 Dark greyish brown stiffclay, gravelly and pebbly near base 3.10 5 -50 SPT at 3.5- 4.0 m (16 blows) GLACIAL SAND AND GRAVEL Reddi sh brown and greyish brown clayey to very cl ayey si lty sand and gravel , beddi ng defined by thin carbonaceous lami nae 4 .OO 9.50 SPT at 6.0- 6.5 m (26 bl ows) 7.5- 8.0 m (13 blows) 9.0- 9.5 m (22 blows) TILL (BOULDER 'CLAY) . Greyish brown pebbly clay, very stiff 2.50 12.00 Borehol e terrni nated at obst ructi on SPT at 10.5-11.0 m (15 blows) Deeside (North Wales) Thematic Geological Mapping I63

Particle size analysisresu7ts

Mean for deposit Depth Percentages percentages bel ow surface (m) Fines Sand Grave7 Fines Sand ve7 Gra

-1/16 +1/16 +1/4 +1 +4 +16 +64 MI -114 -1 -4 -16 -64

19 73 8 6.0-6.5 17 8 3319 16 7 0 7.5-8.0 24 74 2 000 0 8.5-9.0 25 . 62 10 111 0 9 .o-9.5 9 45 35 650 0 Mean 19 47 20 662 0

Thickness Depth (m 1 (m) SJ 27 sw/252 2039 7322 Surface level c + 172 TOP SO I L 0.30 0.30 TILL (BOULDER CLAY) Dark to pale brown pebbly clay with lenses of grave7 ly , sandy clay 2.50 2,80 Sandy stony clay passing into a thin bed of wetbrown sand 0.80 3.60 SPT at 3.0-3A m (21 b7ows) Stiff greyish brown clay with abundant cobbles and large pebbles 4 .OO 7.60 HALKYN FORMATION (Weathered) Dark grey clay with mudstone fragments and coal f ragrnents 1.20 8.80 164 Deeside (North Wales) Thematic Geological Mapping

Thickness Depth (m 1 (m) SJ 27 SEI177 2545 7072 LeadbrookHal 1 Farm Surfacelevel c + 57 MADE GROUND Reddish brown clayey sand with occasional pebbles SPT at 2.0-2.5 m (6 blows) TILL (BOULDER CLAY) Dark reddish brown stony clay with lenses of clayey sand and gravel 12.10 17 so Borehole terminated due to difficult penetration