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Geology of the Leeds district — a brief explanation of the geological map Sheet 70 Leeds

A H Cooper and A Gibson

Bibliographic reference: Cooper, A H, and Gibson, A. 2003. Geology of the Leeds district — a brief explanation of the geological map. Sheet Explanation of the British Geological Survey. 1:50 000 Sheet 70 Leeds (England and Wales).

Keyworth, Nottingham: British Geological Survey © NERC 2004 All rights reserved

Copyright in materials derived from the British Geological Survey's work is owned by the Natural Environment Research Council (NERC) and/or the authority that commissioned the work. You may not copy or adapt this publication without first obtaining permission. Contact the BGS Intellectual Property Rights Section, British Geological Survey, Keyworth, email ipr@bgs.ac.uk. You may quote extracts of a reasonable length without prior permission, provided a full acknowledgement is given of the source of the extract.

(Front cover) Almscliff Crag [SE 2682 4899] massive grits showing tor-like weathering (Photograph A H Cooper; GS 1235).

(Rear cover)

Notes

The word 'district' refers to the area of Sheet 70 Leeds. National Grid references are given in square brackets: all lie with the 100 km square SE. Borehole records referred to in the text are prefixed by the code of the National Grid 25 km² upon which the site lies, for example SE44SW.

Acknowledgements

The authors acknowledge contributions from R D Lake and J I Chisholm to the section on Carboniferous rocks; C P Royles supplied the geophysical description and images. This Sheet Explanation was edited by A A Jackson; Figures were produced by R J Demaine.

The urban area of Leeds was surveyed and described with the support of the Department of the Environment (now Department for the Environment and Regions). We acknowledge the assistance provided by members of the City of Leeds Metropolitan District local authority, the Coal Authority, Mineral Valuers Office, Environment Agency, Yorkshire Water, National Rivers Authority, British Waterways, British Rail (now Railtrack) and numerous civil engineering consultants. Landowners, tenants and quarry companies are thanked for permitting access to their lands.

The grid, where it is used on figures, is the National Grid taken from Ordnance Survey mapping. © Crown copyright reserved Ordnance Survey licence number GD272191/2003.

Geology of the Leeds district (summary from rear cover)

(Rear cover)

The Leeds district includes gritstone moors in the north-west, rolling farmland of the Carboniferous and Permian terrain and low-lying glacial lake deposits of the Vale of York. Leeds city in the south-west of the district developed as a focus for industry, fueled by local coal mining and encouraged by transport along the waterways of the Aire valley. The bedrock of the district divides into three: Carboniferous rocks in the west, Permian in the central part and Triassic strata in the east. Thick glacial deposits occur in the north-east.

The Carboniferous strata are oldest in the north and youngest in the south ranging from about 323 to 310 million years old. In the north, they include the Millstone Grit Group with its massive sandstone units separated by mudstone, siltstone and subordinate coal sequences. The sandstones form moderately elevated ridges with steep scarp slopes, especially overlooking the Wharfe valley. The Coal Measures in the south of the district grade gently down to the Aire valley, and consist of mudstone, siltstone, coal and sandstone.

The Permian is dominated by dolomite sequences separated by mudstone with gypsum. The dolomites form easterly dipping escarpments with steep west-facing scarps. The mudstone and gypsum form clayey valleys between the escarpments. In some places the gypsum is responsible for natural subsidence features. The area is largely arable with some dolomite quarries.

Triassic sandstones in the east of the district are almost completely concealed by thick glacial deposits. Hummocky terrain in the north-east reflects the presence of moraines and eskers. The land in the south-east corner is flat and underlain by clay and sand deposited in a former glacial lake.

The new geological map and this Sheet Explanation provide valuable information on a wide range of earth science issues. These include traditional aspects such as sedimentology and stratigraphy, but also cover applied aspects such as mineral, energy, and water resources, waste disposal, foundation conditions and conservation.

Chapter 1 Introduction

This Sheet Explanation provides a summary of the geology of the district covered by the geological 1:50 000 Series Sheet 70 Leeds published in solid and drift editions in 2002. A fuller description of the geology for the urban area of Leeds can be found in the Technical Reports for the 1:10 000 Series maps and thematic report for planning and development in Leeds (Lake et al., 1992).

Approximately half of the district lies within the administrative area of City of Leeds District of West Yorkshire, and the other half is in North Yorkshire, including parts of Harrogate District Council, Selby District Council and York District Council. The main population centre is the conurbation of Leeds part of which lies in the south-west of the district.

Carboniferous strata crop out in the west of the district, Permian in the centre and Triassic in the east, with a cover of glacial deposits that is particularly thick in the north-east. The Carboniferous strata include the Millstone Grit Group with massive sandstones that form moderately elevated ridges with steep scarp slopes, especially overlooking the Wharfe valley. Southwards, it is overlain by Coal Measures, which are generally softer lithologies consisting of interbedded mudstone, siltstone, coal and sandstone and grade gently down to the Aire valley. The Permian rocks are dominated by dolomite that forms easterly dipping slopes with steep west-facing scarps. Interbedded mudstone and gypsum form clayey valleys between the escarpments. Triassic sandstone in the east of the district is almost completely concealed by thick glacial deposits that give a distinctive character to the landscape. In the north-east, hummocky terrain reflects the presence of moraines and eskers; in the south-east, flat lying clay and sand were deposited in a former glacial lake.

History of research

Sheet 70 Leeds was originally surveyed on a scale of six inches to one mile and published in 1870 at a scale of one inch to one mile (1:63 360) [Old Series] Sheet 93SW. A description of the district was given by Aveline et al. (1870). A resurvey was undertaken between 1931 and 1938 and the first edition of Sheet 70 was published with separate solid and drift editions in 1950, together with a memoir (Edwards et al., 1950). Between 1989 and 1992, the urban area of Leeds was resurveyed; thematic maps were produced and a report to the Department of the Environment (Lake et al., 1992). Subsequently, the remainder of the district was resurveyed. The ground to the south-east of Leeds was surveyed as part of a special study for the Department of the Environment (Barclay et al., 1990) when Sheet 78 Wakefield was also mapped. The geology of the area to the north of Leeds was compiled from information gained from sand and gravel investigation along the River Wharfe (Price et al., 1984) and airborne remote sensing using digital imagery. The digital imagery allowed the 1930s mapping to be checked and modified where necessary. The eastern part of the district was partially resurveyed using aerial photography allied with the interpretation of digital borehole data and a limited amount of resurveying.

Chapter 2 Geological description

During the late Devonian and Dinantian, a phase of crustal stretching resulted in the formation of rapidly subsiding basins that were separated from relatively slowly subsiding horst and tilt-blocks by extensional faults (Leeder, 1982; Kirby et al., 2000). The Leeds district is located mainly within the area of the Harrogate Basin, which is separated from the Askrigg Block by an eastwards extension of the North Craven Fault system (Figure 8). These early basin and block structures strongly influenced the later sedimentation.

Namurian

In previous surveys, the Millstone Grit was defined as a chronostratigraphical unit, the Millstone Grit Series comprising all strata of Namurian age including the dominantly argillaceous Upper Bowland Shales (Edwards et al., 1950). The Millstone Grit Series was subdivided into six groups defined as goniatite genus-zones: the Skipton Moor Grit Group and Upper Bowland Shale (E1), Silsden Moor Grit (E2), Middleton Grit (H), Kinderscout Grit (R1), Middle Grit (R2) and Rough Rock (G1) groups (Stephens et al., 1953). During this resurvey, and following usage in Bradford district to the west, the Millstone Grit Group has been mapped as a lithostratigraphical unit that includes all strata of Namurian age above the base of the Pendle Grit Formation; the Upper Bowland Shale is a formation within the dominantly argillaceous Bowland Shales Group. The term 'grit' is well established in the literature for this area, and consequently grit and sandstone are used synonymous in the following text.

The Namurian Epoch is divided into seven stages, which are in turn subdivided into chronozones (Ramsbottom et al., 1978). The boundaries of these chronostratigraphical subdivisions, are recognised biostratigraphically by the presence of diagnostic ammonoid (goniatite) fauna.

During the Namurian Epoch (about 320 million years ago), northern England lay within a large, actively subsiding basin. Sediments eroded from the surrounding land surfaces to the north were transported by rivers into the basin and deposited as fluvial and deltaic sediments that prograded basinward into turbidite fan deposits. The lithified fluvial and deltaic deposits are mainly sandstones, whereas the fine-grained background deposits that formed in the quiet basin areas are mudstones and siltstones.

The Upper Bowland Shale Formation of Pendleian age consists predominantly of dark grey mudstone, and is approximately 105 to 125 m thick. It is concealed beneath the Millstone Grit Group, but crops out in the Bradford district to the west. The Millstone Grit Group is about 1700 m thick and comprises interbedded mudstone, siltstone and sandstone. The sandstone crops out in natural bluffs (Plate 1) and is exposed in quarries. The Pendle Grit Formation is the lowest unit of the Millstone Grit. It consists of feldspathic, medium to coarse-grained sandstone interbedded with fine-grained sandstone, siltstone and mudstone. Details of the sequence and named sandstones are given in (Figure 1).

Westphalian

The Westphalian strata (around 310 million years old) crop out in the south-western part of the district and are present beneath the Permian rocks in the south-east. These strata represent a change from the deltaic sedimentation of the Millstone Grit Group to shallow-water conditions and subsequent episodic emergence on coastal and delta plains where land floras flourished and died, eventually forming extensive coal seams.

The Coal Measures are divided into the Lower, Middle and Upper formations, but only the Lower Coal Measures (LCM) of Langsettian (Westphalian A) age and the lower part of the Middle Coal Measures (MCM) of Duckmantian (Westphalian B) age are present here. They rest conformably upon the Millstone Grit Group; the base is taken at the base of the Subcrenatum (Pot Clay) Marine Band. The Coal Measures comprise cyclic sequences of interbedded mudstone, siltstone and sandstone with beds of coal, seatearth and ironstone. A typical coarsening-upward cycle comprises grey to black mudstone, weathering to orange-brown and mottled pale grey. It is commonly micaceous with planar lamination, or massive bedding, and containing ironstone nodules. It passes up gradually into siltstone that is typically medium grey, with plant debris, flaser and lenticular bedding, ripple cross-lamination and parallel lamination. The siltstone grades both vertically and laterally into sandstone, and it is this lithology which forms topographical features that allows them to be separated from the interbedded mudstone and siltstone sequences. In the lower part of the succession the sandstones are thin and laterally impersistant, but higher up they are thicker and laterally persistent. The sandstones (Figure 2) are mainly fine grained, varying from very fine to medium grade, and consist mainly of subangular to sub rounded quartz and feldspar grains with a variable mica content. They are grey where fresh, but weather to yellowish brown. Sedimentary structures include planar lamination, cross-lamination and climbing ripples, together with flaser and lenticular bedding. Coalified plant fragments are common and so are trace fossils. Seatearths are also present, characterised by rootlets, which commonly include Stigmaria that grew in the palaeosols during floral colonisation. The seatearths are termed gannisters where they formed in sandstones and fireclays where they formed in mudstone. In these rocks, the disturbance of the palaeosols by plant growth has destroyed the original sedimentary fabric making them more homogeneous, and penecontemporaneous weathering has leached the rock.

Coal seams are widespread, and many are developed on a regional scale. However, they are laterally variable in thickness, composition and in the number of the various 'dirt' partings that they contain. In general, the coal rests on seatearth and thus caps the sedimentary cycle. Twenty-two coals are named in the Lower Coal Measures and nine are recognised in the Middle Coal Measures of the district (Figure 3). Marine bands containing a characteristic fauna (Calver; 1968) represent eustatically controlled flooding events, and thus form widespread marker beds. They usually occur above the coals in the lower part of the sequence, where the Subcrenatum, Honley and Listeri marine bands are present. They are generally 2 to 3 cm thick, but may reach 2 to 3 m in places.

Permian

The Variscan earth movements at the end of the Carboniferous resulted in faulting, folding and uplift. By early Permian times, the land surface took the form of a major land-locked basin extending from eastern England across to Germany and Poland. The Leeds district lay at the western margin of this basin in tropical palaeolatitudes (Smith, 1989). The newly uplifted areas were subjected to severe erosion in a desert environment, and the more resistant Carboniferous sandstones, such as those now found near Wetherby, formed subdued hills (Cooper and Burgess, 1993). The softer Westphalian rocks were worn down to a rocky pediment plain on which breccia accumulated in places. These basal breccias and the desert sand dunes that overlie them make up the Rotliegend Group (Figure 4). In the late Permian, the basin flooded rapidly and became a major enclosed sea. In the hot dry climate evaporation from this sea resulted in the formation of evaporites and dolomites that comprise the Zechstein Group.

Rotliegend Group

At outcrop, from Garforth southward, the Rotliegend Group comprises patchy basal breccia and sandstone that rest unconformably on the Carboniferous strata. The sandstones of the Yellow Sands Formation (formerly the Basal Permian Sands; (Plate 2)) are lenticular in form, with rounded wind-blown grains. In boreholes, they are a light bluish grey in colour due to the oxidation state of the ferruginous component and pellicles that coat the sand (Smith, 1992). At outcrop, along the base of the 'Magnesian Limestone' escarpment, the yellow sands range up to a maximum thickness of about 6 m; at depth, beneath the Vale of York, they increase to about 20 m (with a maximum of 46 m to the north of the district). The sandstones are aeolian in origin and form north–east-trending dune structures or draa.

Zechstein Group

During the Late Permian, the Zechstein Sea inundated the desert landscape burying the hills, sand dunes and breccias. The Leeds district lay at the margin of this sea and organic-rich argillaceous dolomite was deposited in the deeper parts of the basin farther east. Subsequently, evaporation followed by further episodes of flooding, possibly caused by glacio-eustatic changes, led to the deposition of sediments that show a strong cyclic pattern. Smith (1970, 1974, 1989, 1995) recognised five cycles, which he named the English Zechstein Cycles EZ1–EZ5. Tucker (1991) recognised seven 'Sequence-stratigraphic Cycles', ZS1– ZS7. In both schemes, individual cycles show variable associations of evaporitic sedimentation. The order of deposition is interpreted by Smith as the evaporitic cycle carbonate-anhydrite-halite-sylvinite, but Tucker (1991) interprets it as highstand (mainly carbonate) and lowstand (mainly evaporitic) cycles. The carbonate and sulphate phases are generally best developed near the margins of the basin, which approximate to the outcrop in the Leeds district. These two lithologies, along with calcareous mudstone, form most of the Permian succession here; total thickness of the Permian strata is about 150 m. The halite and sylvinite deposits are restricted to the more central parts of the basin near the Yorkshire coast and farther east (Smith 1989; Smith and Taylor, 1992).

The Zechstein Group rests with marked unconformity on the carboniferous rocks and shows a transitional boundary with the overlying Sherwood Sandstone Group. New formation names (Smith et al., 1986) replace the traditional Permian nomenclature, which is given here in parentheses. The Cadeby Formation (formerly Lower Magnesian Limestone) forms a broad outcrop of dolomite and dolomitic limestone in the central part of the district. This formation has a complex diagenetic history and locally includes vugs some of which are mineralised with hematite, galena and copper minerals (Marshall, 1856; Harwood and Smith, 1986). The formation is divided into two members separated by the Hampole Discontinuity. The lower one, the Wetherby Member consists mainly of bedded dolomite with local reef deposits, and broad algal stromatolite domes (Plate 3), such as those exposed along the A1 road cuttings at Aberford. The overlying Sprotbrough Member comprises massive cross-bedded ooidal dolomite formed by deposition as subaqueous ooidal dunes; these can also be seen in the cuttings at Aberford. These members can be recognised in exposures, (Smith, 1974; Smith et al., 1986) but otherwise are impossible to separate into mappable units.

To the east, the Cadeby Formation is overlain by the Edlington Formation (formerly Middle Marl) comprising red calcareous mudstone with gypsum. The Hayton Anhydrite Formation occurs at the base of the Edlington Formation in the subsurface, but towards outcrop it has hydrated to gypsum and is largely dissolved away. The Brotherton Formation (formerly Upper Magnesian Limestone) overlies the Edlington Formation and forms a narrow outcrop. It comprises a thin uniform sequence of dolomitic limestone, but where the underlying gypsum has dissolved, the rock is generally folded and slightly brecciated. It is overlain by the Roxby Formation (formerly Upper Marl), which consists of red calcareous mudstone with gypsum. Like the Edlington Formation, this contains anhydrite and gypsum in the form of the Billingham Anhydrite Formation and the Sherburn Anhydrite Formation. Both these units pass laterally into gypsum up-dip towards outcrop, where they are largely dissolved away causing the overlying strata to founder; continued dissolution yields dissolved calcium sulphate to the local water flow (Cooper, 1986).

Triassic

Sherwood Sandstone Group

During the Triassic period, lithospheric extension and rifting continued on the sites of the former Permian basins. The climatic regime was one of continental desert; sedimentation was mainly aeolian with fluvial red beds that now make up the dominantly arenaceous Sherwood Sandstone Group. In Yorkshire, the Sherwood Sandstone Group ranges up to 400 m thick, but in this district only the lower 75 m is present. It comprises fine to coarse-grained reddish brown, fluvial sandstones. These are commonly cross-stratified and contain channel structures, sporadic layers of mudstone clasts and a few pebbly beds. The Sherwood Sandstone Group is locally important as the major groundwater aquifer.

Quaternary

The Quaternary era (from 1.8 My to 10 000 BP) was characterised by dramatic climatic oscillations that caused repeated ice ages (glacials) separated by temperate (interglacial) phases (Figure 5). Several major glacial periods probably affected the district from the Anglian to the Wolstonian. During the early phases, glacier ice probably covered the entire region, and eroded remnant deposits are preserved in the west of the district mainly as valley fill, and in the east below later deposits. During the younger Devensian Stage, ice cover was less extensive, affecting mainly the Vale of York and the eastern half of the Leeds district (Gaunt, 1976).

The several older phases of glaciation, which probably affected the region are difficult to disentangle, and so are combined as 'pre-Devensian'. Most of the pre-Devensian glacial deposits within the district probably date from the Anglian Stage, several hundred thousand years ago when ice extended as far as southern England. Because of their considerable antiquity, the pre-Devensian deposits are now heavily dissected by erosion and only relicts remain on the plateaux to the west of the Devensian ice limit, which includes the western half of this district. These deposits vary considerably depending on the local bedrock, but generally range from sandy clay to clay, with local and exotic rock clasts.

In the Wortley area of Leeds, (around [SE 285 331]) ancient excavations in the Aire valley yielded the remains of Hippopotamus preserved in clay that was dug from a terrace of the Aire (Edwards et al., 1950). This deposit has been carbon-dated; the results are inconclusive but suggest an Ipswichian age (Figure 5) and indicate that a warm temperate environment prevaled prior to the Devensian ice age.

Devensian

During the last glaciation ice covered most of northern Britain. The Pennines were glaciated as far south as Leeds and a tongue of ice occupied the Vale of York. Within the district, the Devensian ice sheet retreated, perhaps as late as 14 000 years ago, leaving extensive glacial and proglacial deposits.

During the glaciation, the Vale of York ice advanced as far south as Doncaster, and the North Sea ice advanced to Norfolk blocking the drainage through the Humber gap (Figure 6). In front of the ice, fluvioglacial outwash deposits and proglacial lake deposits were formed in the dammed pre-glacial valley system. Subsequently, as the ice advanced to the Devensian maximum at Doncaster (Gaunt 1976, 1994), it overrode these deposits and built up a marginal belt of gravels and till, the Linton-Stutton kame belt (Edwards et al., 1950). The ice then retreated northwards and the lobate York Moraine and Eskrick Moraine mark temporary still-stands in the vale (Figure 6) and (Figure 7). The moraines deposited by this ice sheet cross the north-eastern part of the district. Between and around the moraines, a spread of glacial till with some glacial sand and gravel was deposited. The ice in the Vale of York blocked the Pennine drainage, which spilled southwards through a channel at Spofforth to join the river Wharfe diverted round to the south of the Eskrick Moraine (Figure 7). As a result, the Wharfe valley commonly has a narrow course and is incised into a gorge between Wetherby and Boston Spa. Upstream of Linton, erosion of pre-existing till deposits resulted in erosional terraces that were incised, and at the wider points along the Wharfe valley terraces of sandy gravel were deposited. These deposits grade eastwards into proglacial lake deposits formed in front of, and around, the glacial topography of the York–Eskrick moraines.

The proglacial lake deposits comprise laminated silt and clay with interbedded and overlying sand, especially where drainage from the west entered the lake. Consequently, the sand is concentrated where the Wharfe entered the proglacial lake to the south-east of Tadcaster. Silt and clay glacial lake deposits are present to the south-east of the district southwards from Church Fenton. The sand, silt and clay were once referred to as the '25 foot' drift of the Vale of York or as the deposits of glacial Lake Humber. In the nonglaciated areas, periglacial weathering and solfluxion on the Pennines have produced deposits of head. These include the Collingham Head deposits of the Wharfe valley and the later head deposits that are recognised in many places throughout the area. Periglacial conditions were also ideal for the development of landslips, which developed preferentially on slopes that were mainly steeper than about 10º. They formed in areas covered with either thick till or where there was deeply weathered mudstone on the slopes capped by water-bearing sandstones at the top of the hill. Numerous landslips of this kind are present along the sides of the Wharfe valley.

Late Devensian and Flandrian

In the Late Devensian, the ice retreated from the Humber Gap and the proglacial lake of the Vale of York drained eastwards into the North Sea. The drainage followed its previous course into the vale around the front of the Eskrick Moraine cutting into the glacial till, glaciofluvial outwash terraces and the associated glacial lake deposits. The River Wharfe produced its present flood plain and alluvium; localised peat deposits formed in poorly drained areas.

Artificial (man-made) deposits

The long history of industrial development in the district has left an extensive legacy of human modification of the natural environment. The man-made deposits shown on the map represent those that were identifiable at the date of survey. They were delineated both by recognition in the field and by examination of documentary sources, in particular, topographical maps, aerial photographs and site investigation data. Only the more obvious man-made deposits can be mapped by these methods and the boundaries shown may not be precise. Generally, only the deposits in excess of about 1.5 m thick are shown, and on the 1:50 000 Series map these have been generalised. Because of the time scale over which the survey was undertaken, the mapped distribution is of variable detail and content.

Made ground represents areas where the ground is known to be deposited by man on the natural ground surface. The main categories include:

• civil engineering constructions such as road and railway embankments and reservoir dams
• spoil from mineral extraction industries such as colliery and quarry spoil
• building and demolition rubble
• waste from heavy industries such as foundry sand, slag from ironworks, ash and cinders from factory boilers
• domestic and other waste in raised landfill sites, including those occupying topographical depressions

The most extensive areas of made ground are in the urban areas, where the topographical features associated with specific areas of made ground, especially colliery spoil, have been smoothed over prior to development. In such areas, the extent of made ground is based largely on site investigation data.

Infilled ground comprises areas where the natural ground surface has been removed and the void partly or wholly backfilled with man-made deposits. Mineral excavations and disused railway cuttings have been used in the district for the disposal of waste materials, and some, quarries have been partly filled with spoil after the cessation of mineral extraction. The common types of fill include excavation waste, construction and demolition waste, domestic refuse and industrial waste. Where quarries and pits have been restored and either landscaped or built on, there may be no surface indication of the extent of the backfilled void. The location of these sites is determined from archival sources, in particular, old topographical and geological maps.

Because of restriction due to scale, the 1:50 000 Series Sheet 70 Leeds does not show all the areas of worked ground or disturbed ground, but they are shown on the constituent 1:10 000 scale geological maps, as well as landscaped ground. Worked ground is where material is known to have been removed, for example in unfilled quarries and pits, excavations for roads and railways and general landscaping. Disturbed ground is indicated where ill-defined, surface mineral workings include a complex association of excavations, subsidence induced by near-surface mineral workings and made ground, for example areas of bell pits and shallow mine workings. Landscaped ground comprises those areas where the original surface has been extensively remodelled, and it is impractical or impossible to delineate areas of cut or made ground. Most areas of urban development are associated with landscaped ground.

Structure and concealed geology

The depositional patterns within the district have been influenced by major basement faults, and block and basin structures, which manifest themselves in the surface fault and fold pattern (Figure 8). The Askrigg Block to the north is separated by the Craven Faults from the Harrogate Basin that extends southwards onto the Leeds district (Kirby et al., 2000) and can be seen in the magnetic and gravity maps (Figure 9), (Figure 10). The top of the basement rocks lies at a depth of between 2750 and 4500 m below OD. The district lies within the Harrogate depositional basin, which contains a thick sequence of early Carboniferous strata. The basin was created in an extensional regime that caused major subsidence. Extensional fault movements along a line that approximates with the Leeds monocline have resulted in the preservation of between 1000 and 2000 m of Courceyan to early Chadian rocks in the northern part of the Leeds district (Kirby et al., 2000).

Between 2000 and 3000 m of Dinantian (Courceyan to Brigantian) strata are preserved. These deposits are thickest toward the north of the district, south of the Harrogate anticline and thinnest over the Leeds monocline, thickening again to the south into the area of the Morley–Campsall fold and fault belt. During the Namurian, basement influence on sedimentation was less evident across the district; and between 800 and 1200 m of strata was deposited. By Westphalian times, the influence of the basement structures had become less important and the sequence is fairly uniform in thickness across the area.

In late Carboniferous times, the area was subjected to compressive tectonism related to the Variscan earth movements caused by the closure of the Rheic Ocean and the associated continental collision. This resulted in inversion of the depositional basins and reactivation of basement structures. Along the edges of the blocks and basins en échelon folds developed to the north of the district, against the Askrigg Block. The Leeds monocline with its underlying fault structure extends across the Pennines to the west en échelon with the Pendle Monocline (Kirby et al., 2000). These structures control the northern boundaries to both the Yorkshire and the Lancashire coalfields. Between these coalfields, an anticlinal fold, the Pennine Line, runs approximately north–south up the middle of the Pennines. This fold was partly responsible for controlling the margin of the Permian Zechstein basin, and subsequent tilting produced the easterly dip of the strata on the east of the Pennines. The intersection of the Pennine structure and the Leeds monocline is responsible for the angled termination of the Yorkshire coalfield just west of Bradford.

Normal faults (and associated folding) fall within two main trends, north–west and south–west, which form approximately conjugate sets. Movement on these faults is post-Triassic, probably in Jurassic and Cretaceous times. Minor mineralisation has occurred in the Permian dolomites over the basement structures, and copper mineralisation was recorded at Newton Kyme (Marshall, 1856). This pattern is repeated in several places along the Permian outcrop (Smith and Harwood, 1986).

The magnetic map (Figure 9) shows a marked north–west-trending regional anomaly with several highs. The southerly gradient across this district coincides approximately with the northern edge of the Coal Measures and the southerly facing monocline that crosses the district. However, the main cause of the magnetic anomaly is deep-seated, and interpreted as a basement structure caused by either buried Cambrian magnetic basement, or regionally metamorphosed basement rocks (Lee et al., 1990).

The Bouguer anomaly map (Figure 10) shows a general gradient from the west to east into the Permian Zechstein Basin. The Askrigg Block and Craven faults are shown to the north–west. A well-marked high runs east–west across the district, and this coincides with the southerly facing monocline that marks the northern edge of the Coal Measures.

Chapter 3 Applied geology

Geological factors have exerted considerable influence upon the development of Leeds and the surrounding area. The location of early settlements was determined by the availability of water, building materials and fossil fuels, and major routes have crossed the district since early times (Plate 4). Those same resources were critical in the development of heavy industries that flourished in the area until the middle of the 20th century. Plans for future development are still influenced by these earth science issues but must also consider derelict and despoiled ground, part of the legacy of past industries. The key geological factors summarised in this section have been detailed by Lake et al. (1992) for the Leeds metropolitan area, Lake et al. (1999) for the Wakefield district and by Waters et al. (1999) for the Bradford Metropolitan District.

Mineral resources

Historically, the greatest mineral resource in the region has been fossil fuel. Coal was extracted initially from small opencast sites or bell pits, and eventually developed into a major industry utilising pillar and stall and then longwall mining techniques. In many places, coal seams were worked together with a seatearth or ironstone. A hiatus in mining activity was reached before the Second World War after which operations declined. Significant activity ended in 1981, although some opencast sites are still in operation in deeper excavations; these allow mining even where there is a considerable thickness of overburden. Extractive industries also exploited the Cadeby and Brotherton limestones and sandstones from the Coal Measures, the Millstone Grit and, to a lesser extent, the Yellow Sands Formation; all of these are still worked on a small scale at various sites across the region. Future expansion is unlikely in the foreseeable future, partly because of sterilisation by urban development and previous exploitation, and because of increasing environmental concerns. Mineral deposits of historical importance in the region are listed in (Figure 11).

Water resources

Groundwater abstracted within the district is generally utilised for industrial or agricultural purposes. Domestic consumption is largely catered for by surface reservoirs. Reasonable extraction rates can be maintained from the Coal Measures and Millstone Grit but water at depth is generally hard, of low quality, has high concentrations of dissolved iron compounds and locally high levels of sulphates. High mineral concentrations are generally associated with sites close to or down-dip from coal and evaporite deposits. These units tend to be impermeable; water is stored in the fissures and faults of the sandstone units while siltstone and mudstone tend to act as aquitards or aquicludes. Relatively high hydraulic conductivities can however be achieved in these argillaceaous strata as a result of fissuring, faulting and flooded mine workings. By comparison, the Sherwood Sandstone possesses both fissure and intergranular porosity, and thus has a much greater storage capacity. Within this district, extracted water tends to be hard and can contain excessive amounts of sulphate and nitrate depending upon provenance. The high hydraulic conductivities of all of these units can make them all susceptible to contamination from the ground surface (Lake et al., 1992).

Engineering ground conditions

A broad impression of how a particular unit can be expected to behave under normal conditions can be determined from its lithological and geotechnical characteristics. Such characteristics have been discussed by a number of authors (Barclay et al., 1990; Northmore, 1991). The major geological considerations for development are outlined in (Figure 12), which provides only a guide to each of the units. In addition to the physical properties of the bulk lithology, conditions are also influenced by geological structure, topography, mining, variable depths and degrees of weathering, and human activity; all these factors must be taken into consideration. A site-specific investigation is essential for any major project.

Karstic features

Karstic features are formed by the dissolution of soluble rocks by surface and groundwater percolating along joints and fissures. This process can affect the Permian limestone and dolomite of the district, but is especially prevalent in the gypsum sequences (Cooper, 1986). The dissolution results in rockhead levels that are highly variable; depressions and channels are common with foundering of strata in subsidence hollows, and voids and cavities at depth. Such conditions can reduce bearing capacity and lead to severe differential settlement below heavy structures. Superficial deposits may have infilled hollows so that the topography is subdued and evidence of karst is obscured. In many cases, it is advisable to carry out geophysical surveys prior to any development in order to obtain a detailed image of the rockhead. Swallow holes and depressions associated with karst conditions tend to follow linear patterns indicating that their occurrence is partly controlled by geological structure.

Moisture induced deterioration

Moisture induced deterioration can be a significant problem in excavations and exposures of mudstone in the Coal Measures and Millstone Grit. Rapid deterioration and softening of these rocks occurs when they are relieved of overburden pressure by excavation, and are exposed to water. This process, which may occur very rapidly, can lead to a marked reduction in shear strength and bearing capacity and a loss of side friction for piles. Exposed excavations in these materials must therefore, be covered with protective layers to prevent such deterioration.

Subsidence due to undermining

Subsidence due to undermining can pose a significant risk in the Leeds district. At any location where a workable mineral deposit is at or near outcrop, the possibility that it has been worked must be considered. The main methods of underground extraction used in the Leeds district are shown in (Figure 13). The earliest technique was bell pitting whereby a shaft was sunk up to 10 m below ground level and a seam was worked in a radial pattern up to 6 m from the centre. Poor backfilling methods and materials mean that voids are common in bell pits. Although most unsupported workings will have by now collapsed, the possibility of further settlement or even sudden collapse should be considered by developers. As most bell pitting was carried out before the Mines Register of 1872, the exact location of many is not known; the characteristic surface evidence of small spoil cones or shallow depressions may have been completely removed by subsequent development or agricultural activity. The larger mapped areas of this mining are shown as disturbed ground.

Pillar and stall techniques were widely employed up until the mid 19th century. The method involved leaving pillars of coal unworked to support the roof during working, and was often aided by wooden supports. This method was generally only employed between the depths of 6 to 30 m, below which the supporting pillars must be of a width that makes working uneconomical. Shallower seams were usually worked open cast but in one location, Richmond Hill [SE 313 331], workings were found just 3 m below surface. Workings may collapse by a number of methods. Pillar collapse and squeezing of the roof or floor usually happen soon after working has finished and pose little problem today. Roof and shaft collapses however can happen over 100 years after cessation.

Longwall mining became more popular in the later 19th century. This method involves progressively cutting away a whole coal face, leaving behind a cavity filled only with spoil (or goaf). Collapse of overlying strata into this cavity usually happens within days, with any residual subsidence completed within two years. Areas overlying workings in the Kippax and Garforth areas, however, suffered subsidence six to eight years after mine closure in the mid 1980s.

The stability of any workings is dependant upon their depth, amount extracted, the surrounding geological structure and the quality of reconstitution. Shaft linings and caps may also degrade over time and become susceptible to collapse. Workings may not have been properly backfilled. Even where backfilling has been carried out properly, the material used may be of a lower strength than the overlying strata. Development over such material could lead to compression and further subsidence.

Locating old workings may be difficult, agricultural activity or subsequent development may have radically altered the appearance of worked sites and the authorities responsible for archiving mineral workings records should be consulted prior to any development.

Made ground

Made ground in the district is of varying composition and quality. It typically occurs where disused quarries, pits or natural depressions have been used for landfill or where disused railway cuttings or pits have been infilled in order to level the ground surface. Much existing development is already constructed upon filled ground. Infilling materials range from grouted pea gravel to domestic refuse and hazardous waste. These materials and the method of their emplacement will greatly influence the quality and longevity of the fill. Detailed assessments are required prior to any development on made ground, especially where a change of use is being considered and thus design criteria of the existing fill may not satisfy the requirements of the new use.

Stope stability

Mass movements in the district are generally limited to the Wharfe valley area where landsliding is associated with the mudstone below both the Follifoot and Plumpton Grits. The west Wharfe valley is also affected by landsliding, this is associated with the Millstone Grit. Localised failures associated with sequences below the Rough Rock and with the Edlington Formation occur north-west of Leeds and south-east of Wetherby, respectively.

Large-scale failures are unlikely in this area of low relief, although artificially steepened slopes such as those found in quarries and opencast pits may be prone to falls and topples. Glacial and periglacial deposits within the area should be assumed to contain relict shear surfaces. Changes in loading or hydrological patterns in these areas may reactivate movement and detailed investigations and testing must be carried out in these areas prior to any development.

Pollution potential

In many cases, made ground must be considered to be contaminated land. Colliery spoil typically produces leachates of high acidity, sulphate and heavy metal content which may pose a risk to buried foundations as well as being harmful to the environment. Spoil may also be prone to spontaneous combustion should the iron pyrite contained within it react with acidic water and air. Other types of made ground, including landfill may contain hazardous substances or organic material that will produce methane and other gases upon decomposition. Such gases may be prone to explosion if they are allowed to build up a head of pressure under confinement. Disused mine shafts and adits may act as pathways for the migration and collection of such gases and pollution-rich water.

Information sources

Further geological information held by the British Geological Survey relevant to the Leeds district is listed below. It includes published and unpublished maps, memoirs and reports, and other sources of data held by BGS in a number of collections.

Searches of indexes to some of the collections can be made on the Geoscience Data Index in BGS libraries and on the internet https://www.bgs.ac.uk

The indexes include:

• index of boreholes
• outline of BGS maps at 1:50 000 and 1:10 000 scale and 1:10 560 scale County Series
• chronostratigraphical boundaries and areas from BGS 1:625 000 maps
• geochemical and other sample locations on land
• aeromagnetic and gravity data recording stations
• land survey records

Maps

Geology maps

1:1 500 000

• Tectonic map of Britain, Ireland and adjacent areas, 1996

1:625 000

• Solid geology map UK South Sheet, 2001 Quaternary geology, UK South Sheet, 1977

1:250 000

• Sheet 53N 02W, Humber-Trent, Solid Geology, 1983

1:50 000 and 1:63 360

• Sheet 70 Leeds; Solid & Drift, 2002
• Sheet 61 Pateley Bridge (1:63 360 scale, hand coloured, out of print)
• Sheet 62 Harrogate; Solid, 1987; Drift, 1987
• Sheet 63 York; Solid & Drift, 1983
• Sheet 69 Bradford; Solid; Solid & Drift, 2000
• Sheet 71 Selby; Solid & Drift, 1973
• Sheet 77 Huddersfield; Solid & Drift, 1978
• Sheet 78 Wakefield; Solid & Drift, 1998
• Sheet 79 Goole; 1:63 360 scale, Solid & Drift, 1972

Digital map information is available for all the above maps.

1:25 000 and 1:50 000 Thematic Maps

• Leeds: BGS Technical Report, WA/92/1 Garforth–Castleford–Pontefract, WA/91/44

1:10 000 and 1:10 560

Details of the original geological surveys are listed on editions of the 1:50 000 or 1:63 360 geological sheets. Copies of the fair-drawn maps of these earlier surveys may be consulted at the BGS Library, Keyworth.

The maps covering the 1:50 000 Series Sheet 70 Leeds are listed below together with the surveyor's initials and the date of survey. The surveyors were: I C Burgess, A H Cooper, R G Crofts, M T Dean, R A Ellison, R D Lake, D H Land, D J Lowe, and D G Tragheim. The maps are not published, but are available for public reference in BGS libraries in Keyworth and Edinburgh and the London Information Office in the Natural History Museum, South Kensington, London. Uncoloured photo copies are available for purchase from BGS Sales Desk; some sheets are available in a digital format including the marginalia (marked with *) and the remainder are available as digital 1:10 000 scale information for the map face only.

Geophysical maps

1:1 500 000

• British Geological Survey, 1997. Colour Shaded Relief Gravity Anomaly Map of Britain, Ireland and adjacent areas. Smith I F, and Edwards, J W F (compilers) 1:500 000 scale (Keyworth, Nottingham, United Kingdom: British Geological Survey). Published 1997.
• British Geological Survey, 1998. Colour Shaded Relief Magnetic Anomaly Map of Britain, Ireland and adjacent areas. Royles, C P, and Smith, I F (compilers) 1:1 5000 000 scale (Keyworth, Nottingham, United Kingdom: British Geological Survey). Published 1998.

1:625 000

• Aeromagnetic map of Great Britain (and Northern Ireland), South Sheet, 1965 Bouguer anomaly map of the British Isles, Southern Sheet, 1986

1:250 000

• Sheet 53N 02W Humber-Trent, Aeromagnetic anomaly, 1977
• Sheet 53N 02W Humber-Trent, Bouguer gravity anomaly, 1977

Geochemical atlases

1:250 000

Point-source geochemical data processed to generate a smooth continuous surface presented as an atlas of small-scale colour-classified digital maps. Geochemical Survey Programme data are also available in other forms including hard copy and digital data.

Hydrogeological maps

1:625 000

• Sheet 1 (England and Wales) 1977

1:100 000

• Southern Yorkshire and adjoining areas (Sheet 12), 1982
• Groundwater Vulnerability Map, South Pennines (Sheet 11), prepared by the Soil Survey and Land Research Centre and BGS for the Environment Agency.

Books

• British Regional Geology
• Pennines and adjacent areas, fourth edition, 2002

Memoirs

• Geology of the country around Harrogate (Sheet 62), 1993
• Geology of the country between Bradford and Skipton (Sheet 69), 1953
• Geology of the Bradford district (Sheet 69), 1999
• Geology of the district north and east of Leeds (Sheet 70), 1950
• Geology of the country around Huddersfield and Halifax (Sheet 77), 1930 Geology of the country around Wakefield (Sheet 78), 1940
• Geology of the country around Goole, Doncaster and the Isle of Axholme (Sheets 79 & 88) 1994
• Geology of the country between York and Hull, 1886
• Geology of the Yorkshire Coalfield, 1878 Concealed Coalfield of Yorkshire and Nottinghamshire, 1951
• Directory of Mines and Quarries, fifth edition. 1998
• The structure and evolution of the Craven Basin and adjacent areas, Subsurface Memoir, 2000.

Technical Reports

Technical reports relevant to the district are arranged below by topic. Most are not widely available, but may be purchased from BGS or consulted at BGS and other libraries.

Geology

Technical reports describing the geology are listed with the details of the 1:10 000 scale geological sheets.

Geology and land-use planning

Parts of the district are covered by the BGS Technical Report and accompanying thematic geological maps dealing with land-use planning and development (Barclay et al., 1990; Lake et al., 1992).

Mineral resources

Price et al. (1984) provides details of sand and gravel resources in Wharfedale. Further information on mineral resources is available from BGS Keyworth.

Engineering geology

Further information on engineering geology is available from BGS Keyworth, and see Northmore, 1991.

Geophysics and Deep Geology

Kirby et al. (1994) provides information on the structural evolution and geometry of the Craven Basin.

Biostratigraphy

There is a collection of internal British Geological Survey biostratigraphical reports, details of which are available from BGS Keyworth.

Documentary collections

Boreholes and shafts

Borehole and shaft data for the district are catalogued in the BGS archives (National Geosciences Records Centre) at Keyworth on individual 1:10 000 scale sheets. For the Leeds district the collection consists of the sites and logs of about 11 000 boreholes, for which index information has been digitised and about 1300 in the north-east of the district which have digitised downhole information. Drillcore is archived from 22 boreholes.

Geophysics

Gravity and aeromagnetic data are held digitally in the National Gravity Databank and the National Aeromagnetic Databank at BGS Keyworth. Seismic reflection data are available for the whole area, except for a gap in coverage in the south-west. These have been acquired in surveys for hydrocarbon exploration by RTZ, Taylor Woodrow and other operators. These data have been used to constrain the sub-surface structural interpretation.

Hydrogeology

Data on water boreholes, wells and springs and aquifer properties are held in the hydrogeology database at British Geological Survey, Hydrogeology, Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OX0 8BB. Telephone 01491 838800.

BGS Lexicon of named rock unit definitions

Definitions of the named rock units shown on BGS maps, including those shown on the 1:50 000 Series Sheet 70 Leeds are held in the Lexicon database. Information on the database can be obtained from the Lexicon Manager at BGS Keyworth. The database can be consulted on the BGS web site: https://www.bgs.ac.uk.

Material collections

Palaeontological collection

Macrofossils and micropalaeontological samples for 168 localities collected from the district are held at BGS Keyworth. Enquiries concerning all the macrofossil material should be directed to the Curator, Biostratigraphy Collections, BGS Keyworth.

Petrological collections

Hand specimens and thin sections are held in the England and Wales Sliced Rocks collection at BGS Keyworth. A collection database is maintained and charges and conditions of access to the collection are available on request from BGS Keyworth.

BGS (Geological Survey) photographs

Copies of photographs used in this report are deposited for reference in the BGS Library, Keyworth. Colour or black and white prints and transparencies can be supplied at a fixed tariff.

Other relevant collections

Coal abandonment plans

Copies of all known abandonment plans are held by the Mining Records Office, Coal Authority, Bretby Business Park, Ashby Road, Burton upon Trent, Staffordshire, DE15 0QD. These plans are held by the Coal Authority in the public domain, but are not available for reference at BGS.

Groundwater licensed abstractions, catchment management plans and landfill sites

Information on licensed water abstraction sites, for groundwater, springs and reservoirs, Catchment Management Plans with surface water quality maps, details of aquifer protection policy and extent of Washlands and licensed landfill sites are held by the Environment Agency.

Earth Science Conservation Sites

Information on the Sites of Special Scientific Interest present within the Leeds district is held by English Nature, Headquarters and Eastern Region, Northminster House, Peterborough, PE1 1UA.

References

Most of the references listed below are held in the Library of the British Geological Survey at Keyworth, Nottingham. Copies of the references can be purchased subject to availability or to the current copyright legislation.

Aveline, W T, Green, A H, Dakyns, J R, Ward, J C, and Russell, R. 1870. The geology of the Carboniferous rocks north and east of Leeds and the Permian and Triassic rocks about Tadcaster. Memoir of the Geological Survey of Great Britain, Quarter Sheet 93S W.

Barclay, W J, Ellison, R A, and Northmore, K J. 1990. A geological basis for land-use planning: Garforth–Castelford-Pontefract. British Geological Survey Technical Report, WA/90/3.

Calver, M A. 1968. Distribution of Westphalian marine faunas in Northern England and adjoining areas. Proceedings of the Yorkshire Geological Society, Vol. 37, 1–72.

Cooper, A H, and Burgess, I C. 1993. Geology of the country around Harrogate. Memoir of the British Geological Survey, Sheet 62 (England and Wales).

Cooper, A H. 1986. Foundered strata and subsidence resulting fron the dissolution of Permian gypsum in the Ripon and Bedale areas, North Yorkshire. 127–139 in Harwood, G M, and Smith, D B (editors). The English Zechstein and related topics. Geological Society of London, Special Publication, No. 22.

Edwards, M A, Mitchell, G H, and Whitehead, T H. 1950. Geology of the district north and east of Leeds. Memoir of the Geological Survey of Great Britain, Sheet 70 (England and Wales).

Gaunt, G D. 1976. The Devensian maximum ice limit in the Vale of York. Proceedings of the Yorkshire Geological Society. Vol. 40, 631–637.

Gaunt, G D. 1994. Geology of the country around Goole, Doncaster and the Isle of Axholme. Memoir of the British Geological Survey, Sheets 79 and 88 (England and Wales).

Godwin, C G. 1994. Mining in the Elland Flags: a forgotten Yorkshire industry. Report of the British Geological Survey, No. 84/4, 1–17.

Harwood, G M, and Smith, F W. 1986. Mineralization in Upper Permian carbonates at outcrop in eastern England. 103–111 in Harwood, G M, and Smith, D B (editors). The English Zechstein and related topics. Geological Society of London, Special Publication, No. 22.

Kirby, G A, Baily, H E, Chadwick, R A, Evans, D J, Holliday, D W, Holloway, S, Hulbert, A G, Pharaoh, T C, Smith, N J, Aitkenhead, N, and Birch, B. 2000. The structure and evolution of the Craven Basin and adjacent areas. Subsurface Memoir of the British Geological Survey. (London: The Stationery Office.)

Lake, R D. 1999. The Wakefield District —a concise account of the geology. Memoir of the British Geological Survey, Sheet 78 (England and Wales).

Lake, R D, Northmore, K J, Dean, M T, and Tragheim, D G. 1992. Leeds: a geological background for planning and development. British Geological Survey Technical Report, WA/92/1.

Lee, M K, Pharaoh, T C, and Soper, N J. 1990. Structural trends in central Britain from images of gravity and aeromagnetic fields. Journal of the Geological Society of London, Vol. 147, 241–258.

Leeder, M R. 1982. Upper Palaeozoic basins of the British Isles — Caledonide inheritance versus Hercynian plate margin processes. Journal of the Geological Society of London, Vol. 139, 479–491.

Marshall, W. 1856. Notice of carbonate of copper occurring in the Magnesian Limestone at Newton Kyme, near Tadcaster. Transactions of the Geological Society of London, Vol. 2, 140.

Northmore, K J. 1991. The engineering geology of south-central Leeds. British Geological Survey Technical Report. WN/91/11

Price, D, Carruthers, R M, Lowe, D J, and Pattison, J. 1984. The sand and gravel resources of the Wharfe valley between Ilkley and Collingham. (Keyworth, Nottingham: British Geological Survey.)

Smith, D B. 1989. The late Permian palaeogeography of north-east England. Proceedings of the Yorkshire Geological Society, Vol. 47, 285–312.

Smith, D B. 1970. The palaeogeography of the British Zechstein. 20–23 in Third symposium on salt, Vol. 1, Rau, J L, and Dellwig, L F (editors). (Cleveland, Ohio: Northern Ohio Geological Society.)

Smith, D B. 1974. Permian. 115–144 in Geology and mineral resources of Yorkshire. Rayner, D H, and Hemingway, J E (editors). (Leeds: Yorkshire Geological Society.)

Smith, D B. 1992. Permian. 275–305 in Geology of England and Wales. Duff, P Mc L D, and Smith, A J (editors). (London: The Geological Society, London.)

Smith, D B. 1995. Marine Permian of England. Joint Nature Conservation Committee. (London: Chapman & Hall.)

Smith, D B, and Taylor, J C M. 1992. Permian. 87–96 in Atlas of palaeogeography and lithofacies. Cope, J C W, Ingham, J K, and Rawson, P F (editors). Geological Society of London. Memoir, No. 13.

Smith, D B, Harwood, G M, Pattison, J, and Pettigrew, T. 1986. A revised nomenclature for Upper Permian strata in eastern England. 9–17 in The English Zechstein and related topics. Harwood, G M, and Smith, D B (editors). Geological Society of London, Special Publication, No. 22.

Stephens, J V, Mitchell, G H, and Edwards, W. 1953. Geology of the country between Bradford and Skipton. Memoir of the Geological Survey of Great Britain. 1:50 000 Sheet 69 Bradford (England and Wales).

Tucker, M E. 1991. Sequence stratigraphy of carbonate-evaporite basins: models and application to the Upper Permian (Zechstein) of northeast England and adjoining North Sea. Journal of the Geological Society of London, Vol. 148, 1019–1036.

Warrington, G, and Ivimey-Cook, H C. 1992. Triassic. 97–106 Atlas of palaeogeography and lithofacies. Cope, J C W, Ingham, J K, and Rawson, P F (editors). Geological Society of London. Memoir, No. 13,

Waters, C N. 1999. Geology of the Bradford district — a brief explanation of the geological map. Sheet Explanation of the British Geological Survey 1:50 000 Sheet 69 Bradford (England and Wales).

Index to the 1:50 000 series maps of the British Geological Survey

The map below shows the sheet boundaries and numbers of the 1:50 000 Series geological maps. The maps are numbered in three sequences, covering England and Wales, Northern Ireland, and Scotland. The west and east halves of most Scottish 1:50 000 maps are published separately. Almost all BGS maps are available flat or folded and cased.

(Index map)

The area described in this sheet explanation is indicated by a solid block.

British geological maps can be obtained from sales desks in the Survey's principal offices, through the BGS London Information Office at the Natural History Museum Earth Galleries, and from BGS-approved stockists and agents.

Northern Ireland maps can be obtained from the Geological Survey of Northern Ireland.

Figures and plates

Figures

(Figure 1) Main named sandstone units in the Namurian sequence of the district.

(Figure 2) Main named sandstones in the Westphalian sequence of the district.

(Figure 3) Thickness of coal seams in the district.

(Figure 4) Permian and Triassic sequence in the district.

(Figure 5) Quaternary sequence in the district.

(Figure 6) Glacial geology of the district.

(Figure 7) Schematic cross-section through the York moraine and the Eskrick moraine.

(Figure 8) Structure of the Leeds district and surrounding area.

(Figure 9) Total field magnetic anomalies in nanotesela (nT) relative to a local variant of IGRF90. Shaded relief map illuminated from the north. Contour interval 10 nT.

(Figure 10) Bouguer gravity anomalies in milligals (mGal) calclulated against the Geodetic Reference System 1967 referred to the National Gravity Reference Net 1973, a variable reduction density has been used. Contour interval 1 mGal (1 × 10⁻⁵ m/s²). Shaded relief map, illuminated from the north.

(Figure 11) Principal mineral resources of historical importance in the district.

(Figure 12) Engineering characteristics of the principal geological units in the district.

(Figure 13) Cross-section subsidence features resulting from coal extraction.

Plates

(Plate 1) Almscliff Crag [SE 2682 4899] 1.5 km north-north-west of Huby. These massive sandstones are part of the Warley Wise Grit and are Namurian in age (GS 1236).

(Plate 2) Permian Cadeby Formation (1.8 m exposed) resting on the Yellow Sands Formation (3 m exposed), Parlington Junction, [SE 4209 3453] north-east of Garforth. The hammer handle is 32 cm long and lies just below the contact (GS1237).

(Plate 3) Dome-like algal stromatolites in the Permian Cadeby Formation (formerly Lower Magnesian Limestone) cut through at an oblique angle by the road cutting for the A1, Aberford, west of road [SE 4361 3711]. Scale rule is 1 m long (GS1238).

(Plate 4) Parlington Junction on the A1 [SE 4209 3453]. This major trunk road, which crosses the district, continues to be developed. Permian Yellow Sands Formation (4 m exposed) is overlain by the Cadeby Formation (1.2 m exposed). The surveyor's green line is approximately along the contact of the two formations. (GS 1239).

(Geological succession) Summary of the geological succession of the Leeds district.

(Front cover) Almscliff Crag [SE 2682 4899] massive grits showing tor-like weathering (Photograph A H Cooper; (GS 1235).

(Rear cover)

(Index map) Index to the 1:50 000 Series maps of the British Geological Survey

Figures

(Figure) 1 Main named sandstone units in the Namurian sequence of the district.

(Figure 2) Main named sandstones in the Westphalian sequence of the district.

(Figure 3) Thickness of coal seams in the district.

(Figure 4) Permian and Triassic sequence in the district.

(Figure 5) Quaternary sequence in the district.

(Figure 11) Principal mineral resources of historical importance in the district.