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Geological notes and local details for 1:10,000 sheets: SP38SW (Coventry North). Part of 1:63,360 Sheet 169 (Coventry). British Geological Survey Technical Report WA/89/25

R A Old

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British Geological Survey Onshore Geology Series Technical Report WA/89/25

Bibliographic reference Old, R.A., 1989Geological notes and local details for 1:10,000 sheets: SP38SW (Coventry North). British Geological Survey Technical Report

© Crown Copyright 1989 Keyworth, Nottingham, British Geological Survey, 1989

Geographical Index UK, Central England, Warwickshire

Subject Index Geology, Quaternary, Triassic, Upper Carboniferous, Cambrian

Production of this report was partly funded by the Department of the Environment, but the views expressed in it are not necessarily those of the Department.

Summary

The geology of Sheet SP38SW (Coventry North) is described with emphasis on significant exposed sections and borehole logs.

The Cambrian and older Carboniferous formations are known only from boreholes, shaft sections and underground mine workings. The top of the Keele Formation, the lower formations of the Enville Group and the basal part of the Bromsgrove Sandstone all crop out in this area, but are generally poorly exposed.

The lithologies of the extensive glacial and post-glacial deposits are described.

Important coal reserves underlie the area; other mineral and groundwater resources are described and a full schedule of boreholes is appended.

Introduction

This report describes the geology of 1:10 000 Sheet SP38SW (Coventry North) (Figure 1), which lies within 1:50 000 geological sheet 169 (Coventry). The area was first geologically surveyed on the one-inch scale by H H Howell and was included in Old Series One-Inch Sheets 53 and 63SW published in 1855. An explanatory memoir for the Warwickshire Coalfield was published soon after (Howell, 1859). The primary six-inch survey was made by C H Cunnington and T Eastwood in 1913–14, and some local details are given by Eastwood and others (1923). An account of the Warwickshire Coalfield, again with some local details, is given by Mitchell (1942). The whole are was surveyed at 1:10 000 in 1986–88 by R A Old.

The mapping and production of this report were completed under a contract jointly funded by the Department of the Environment, and the British Geological Survey. Palaeontological contributions to this report are by Drs N J Riley and A W A Rushton.

Copies of this report and uncoloured dyeline copies of the 1:10 000 map may be purchased from the British Geological Survey, Keyworth.

Similar reports covering adjoining 1:10 000 sheets are:

SP 28 SE Allesley (Rees, 1989)

SP 37 NW Coventry Central (Old, 1988)

SP 38 NW Bedworth West (Bridge, 1989)

SP 38 SE Coventry North-East (Bridge, 1988)

An account of the whole area of the contract is given by Old and others (1989).

Geological sequence

The Quaternary deposits, Bromsgrove Sandstone, Coventry Sandstone and the upper part of the Keele Formation are represented at outcrop. The remaining parts of the sequence are known only from boreholes.

Cambrian

Cambrian rocks have been penetrated beneath Coal Measures in seven British Coal boreholes, but specimens were preserved from only three of these and the logs of the remainder are of poor quality. The junction between the Monks Park Shales and the overlying Merevale Shales is drawn tenatively NE–SW from just to the south of the Hollyfast Borehole [3302 8369] to Keresley (Old and others, 1987 p.4).

The Monks Park Shales recorded in the Hollyfast and Hazel Grove [SP 3015 8375] boreholes, are dark grey fissile mudstones with minor pale grey siltstone bands and laminae. At Hollyfast these yielded an acrotretid brachiopod and ‘Prooneotodus’.

The Merevale Shales recorded, from the Birch Tree Farm Borehole [SP 3102 8288], consist of medium grey-green fissile mudstone, with numerous burrows and trails, and yield a few tiny sponge spicules.

Post-Cambrian sills

The Hazel Grove and Hollyfast boreholes both encountered sills (0.5 m and 1.2 m thick respectively) cutting the Cambrian. Neither sill has been examined in thin section, but they are probably altered lamprophyres similar to those known at outcrop near Nuneaton (Taylor and Rushton, 1971). The sill at Hazel Grove exhibits 'saw-tooth' contacts with the Cambrian mudstone, implying that the latter was lithified before intrusion occurred. In detail, however, the same contacts show slight lobate protrusions of igneous rock into mudstone, suggesting that lithification was incomplete, and that the sill is of late-Cambrian age.

The mudstone adjacent to the sills is baked, and patches and veins of pyrites have developed.

Upper Carboniferous (Westphalian)

The Westphalian beds rest directly on Cambrian strata; below the upper part of the Keele Formation they do not come to crop in the area, but are known only from boreholes (Figures 2 to 4). The sequence consists mainly of mudstones, siltstones and seatearths. The Productive Coal Measures and the Halesowen Formation are grey-coloured and coal-bearing; the intervening Etruria Marl Formation is variegated grey, green and red brown. The Keele Formation and the Coventry Sandstone consist almost entirely of red measures, predominantly argillaceous in the former and arenaceous in the latter. The only well identified Westphalian subdivision is that between Westphalian B and C marked by the Aegiranum Marine Band, some 10–50 m below the Etruria Marl. Brief accounts of the Keresley 1A and Whitmore Park boreholes are given by Gibson (1915), and of the Coventry Colliery shafts by Eastwood (1920).

Productive Coal Measures

The Productive Coal Measures include all the Westphalian below the Etruria Marl. Because the Vanderbeckei Marine Band is not developed in this area the position of the Westphalian A/B boundary is uncertain. In those areas of the Warwickshire Coalfield where the marine band has been proved, it lies just above the Seven Feet coal (Cope and Jones, 1970).

The beds below the Thick Coal are typically 45 to 50 m thick, but increase locally to 80 m around Hazel Grove (Figure 2). They consist of grey mudstone, siltstone, seatearth, impersistent sandstone and numerous, mainly thin, coal seams. Near the base of the sequence a group of three coal seams occurs, known collectively as the Bench. At Hazel Grove the Bench consists of an upper leaf of 1.16 m and a lower leaf of 1.44 m separated by 2.44 m of mudstone and seatearth. Elsewhere the leaves are much thinner.

A 0.6 m seam 25 m above the Bench at Hollyfast, and a 0.4 m seam 21 m above the Bench in the Coventry Colliery South Exploration Drift [SP 3250 8382], are tenatively correlated with the Double.

The Seven Feet varies in thickness from 0.5 to 1.0 m, and is usually 5 to 8 m below the Thick Coal. In the Hollyfast and Hazel Grove boreholes the interval increases to about 30 m, and mudstones close above the Seven Feet contain non-marine bivalves.

The Thick Coal is the only seam of economic importance in the area (see Economic Geology). It is an amalgamation of seven seams, each of which is named separately in other parts of the Warwickshire Coalfield where there are intervals of other rocks between the seams (Cope and Jones, 1970; Old and others 1987). In ascending order the constituent seams are: Smithy, High Main, Nine Feet, Ell, Ryder, Bare, Two Yard and Thin Rider, although Fulton (1987) excludes the Smithy.

All the above seams are probably present in the area, but they are not clearly identified in the older records, and the more recent records are confidential. The Thick Coal is generally 5 to 6 m thick except at Hazel Grove where the seams below the Two Yard are absent, due to a combination of faulting and lateral passage into mudstone and siltstone. A few small washouts are shown on the Two Yard working plans of Coventry Colliery.

The Productive Coal Measures above the Thick Coal are from 58 to 100 m thick, the variations being mainly due to the diachronous base of the Etruria Marl. The beds are predominantly grey mudstone, seatearth and siltstone, and thin impersistent coals, of which only the Half Yard and Four Feet are named. There is appreciably more sandstone than in the beds below (Figure 2).

Mitchell (1942, p.22) records Carbontcola cf. aquilina in the roof of the Two Yard at Coventry Colliery, and British Coal borehole logs indicate sporadic non-marine bivalves, notably in the roof of the Thick Coal and above the Four Feet or its probable horizon. A marine band is also recorded by British Coal in the Brownshill Green Farm [SP 3069 8263] and Rookery Farm [SP 3106 8161] boreholes, 24 m and 15 m above the Thick Coal respectively, but no specimens were collected. The Aegiranum Marine Band is widespread, although it was not recorded at Rookery Farm, and is apparently replaced by a wash-out in the Coventry No. 2 Shaft. The only faunas collected were from the Birch Tree Farm Borehole and await identification. On the basis of British Coal logs Fulton (1988) considers that the faunal facies of the Aegiranum Marine Band is "fully marine, Productoid’. Vernon (1912, p 619) records Sphenophyllum mysiophyllum 19 m above the Thick Coal in the Keresley 1A Borehole.

Etruria Marl Formation

The Etruria Marl is between 33 and 76 m in thickness. There is a gradual passage upwards from grey Productive Coal Measures to multicoloured Etruria Marl, and the boundary is diachronous (Figure 2). The top of the Formation is usually marked by a massive sandstone at the base of the Halesowen Formation, but locally in the north (Figure 2) that sandstone is absent, and there is a gradual passage upwards from grey and brown mudstone to grey mudstone.

The Etruria Marl consists of mudstone and seatearth, either grey, or variegated in shades of red, brown, purple and, green-grey. Up to half the Formation consists of sandstones, which are generally coarse and gritty, pale grey, micaceous and false-bedded. They may include mudstone clast breccias, or 'espleys', containing ironstone pebbles and clasts of green and red mudstone, some of which may have been derived from Cambrian rocks. The 0.5 m coal near the base of the Formation in the Birch Tree Farm Borehole is exceptional.

Halesowen Formation

Complete Halesowen Formation successions have been recovered at four localities (Figure 3). The base of the Formation has also been cored in the other coal exploration boreholes (Figure 2).

The base of the Formation is normally taken at the base of a thick, massive sandstone overlying variegated mudstone of the Etruria Marl. Locally, where this sandstone is absent (Figure 2), the junction is gradational. The top of the Formation is known with much less precision. Of the four sections shown in Figure 3 only that at Birch Tree Farm has been reliably recorded. The predominantly pale grey Halesowen mudstones give way upwards, over about 25 m, to interbedded grey, chocolate brown and multicoloured mudstones, and finally to predominantly chocolate brown mudstones at the base of the Keele Formation. The Halesowen sandstones are generally coarse-grained and micaceous, while those in the Keele Formation are red-brown and non-micaceous. At Birch Tree Farm the top of the Halesowen Formation is placed above the highest sandstone of ‘Halesowen’ type. Another indication of the top of the Formation, useful in uncored boreholes, is a distinctive high gamma ray value recorded throughout the area and beyond. In the Birch Tree Farm Borehole the gamma peak occurs 48 m below the base of the Keele Formation, and it is assumed to be in the same position in the uncored boreholes. As defined above, the Formation varies in thickness from 110 to 165 m.

The sandstones, dominant in the lower part of the Formation, are pale-grey, coarse-grained and micaceous. Individual units commonly exhibit erosive bases, a calcareous cement or calcareous nodules, and coaly plant debris. Intraclast mudstone breccias are also common, and the ‘conglomerates’ of some of the older logs may be similar breccias.

The remaining beds are mainly grey or grey-green mudstones with lesser amounts of seatearth and siltstone. Red or multicoloured mudstones occur sporadically, and increase in abundance towards the top of the Formation. There are a few thin coal seams of which the lowest, in the Keresley 1A Borehole and Coventry Shafts, may be the Milton, a seam which is developed widely in the area to the south (Old and others, 1987). Vernon (1912, pp 619–620) records Asterotheca (Pecopteris) miltoni and Sphenophyllum emarginatum at 509 m in the Whitmore Park Borehole.

Keele Formation

The upper part of the Keele Formation comes to crop in the north-east of the area, and the complete sequence is known from borehole and shaft sections. The Formation consists of 155 to 220 m of alternating red-brown mudstone and sandstone, and is generally more argillaceous than the formations above and below. As described earlier, the junction with the Halesowen Formation is gradational, and in uncored boreholes cannot be positioned accurately. In the Birch Tree Farm Borehole the mudstones in the basal 50 m are chocolate-brown, while those above are red-brown. The top of the Formation is placed beneath the thick basal sandstone of the Coventry Sandstone. Besly (1988) reviewed the palaeontological evidence for the age of the Keele Formation, and concluded that it ranges from late Westphalian D to late Stephanian or possibly early Autunian.

The cores of the Birch Tree Farm Borehole reveal that the whole Formation is noticeably more calcareous than those above and below. Calcareous nodules, probably of pedogenic origin, are common and many of the sandstones have a calcareous cement. Mudstone beds commonly show desiccation cracks and green reduction spots. The sandstones are typically cross bedded, and some include intraclast mudstone breccias and conglomerates.

There are very few exposures in the area of outcrop. The much-publicised brickworks at Longford [SP 349 842] is now entirely back-filled. The following section is given by Eastwood and others (1923, p 81).

The limestone bed, which lies about 50 m below the top of the Formation, was named the ‘Whitacre–Longford Limestone’ (Eastwood and others, 1923 p 88), and specimens collected in 1914 yielded Spirorbis sp., Carbonita fabultna, C. pungens and Anthracopupa sp. (BGS collections). Vernon (1912, pp 612, 620) collected Asterotheca (Pecopteris) arborescens, A (P) miltoni and Acttheca (P) polymorpha about 3 m above the limestone, and Dix (1935) obtained A. cf. hemitelotdes, Odontopteris cf. schlotheimt, 0. sp., Cordattes cf. lingulatus and Calamites sp.

Eastwood (1920) considered the 0.3 m of ‘grey sandstone’ recorded in the Coventry Colliery No. 1 Shaft, 50 m below the top of the Formation, probably represents the Whitacre–Longford Limestone.

Another limestone occurs 14 m below the top of the Formation in the Whitmore Park Borehole (Gibson, 1915), and close below the Coventry Sandstone in the Courtaulds' Little Heath Wells (e.g. No. 3; Figure 4). It was incorrectly correlated by Gibson (1915) with a limestone in the Keresley 1A Borehole,

Enville Group

Coventry Sandstone Formation

Almost the whole area is underlain by the outcrop of the Coventry Sandstone Formation, all of which is represented apart from the top 15 m. The Formation consists of about 520 m of red-brown sandstones with interbedded mudstones, some of which combine to form thick units (Figure 4). There are a few conglomerates and pebbly sandstones, notably in the Corley Member and towards the base of the Formation. The junction with the Keele Formation is taken where thickly bedded sandstone gives way downwards to mudstones and thin sandstones.

Beds below the Corley Member

Comparative sections of these beds are shown in Figure 4. The sandstone units within this sequence are imperstent , as is well illustrated by the outcrops north of Rowley's Green [SP 24 84]. Conglomerate lenses, which crop out here about 80 m above the base of the Formation, probably represent point bar deposits. Similar conglomerates occur somewhat lower in the sequence in the Whitmore Park Borehole and Coventry No. 1 Shaft (Figure 4). The conglomeratic beds were included in the ‘Sandstone and conglomerates of Arley and Exhall’ by Eastwood (1923, p.77) but he also (p.82) termed these beds the ‘Arley and Exhall Conglomerates’ and placed them, incorrectly, at the base of the Corley (Enville) Group (1923, plate VIII). Shotton (1927) followed the latter terminology and stratigraphy. However, because of their impersistence, it is doubtful whether the conglomerates have any value for stratigraphical correlation.

Conglomerate boulders in fields around Barratt's Farm [SP 340 844] contain well rounded pebbles up to 3 cm in diameter, mainly of fine-grained, brown quartzose sandstone, orange chert and grey Carboniferous Limestone. Shotton (1927) concludes that the sandstones are derived from Silurian outcrops and gives (p.612) a pebble count for a conglomerate ‘about a mile and a half south-south-east of Exhall’ ?[SP 345 822] as follows: limestone 46%, chert 36% and quartz and quartzite making up most of the remainder. The ‘quarry near Exhall’ which yielded Calamites and Lepidodendron (Ramsey, 1855), Sternbergta (Phillips, 1871, pp.95–6), and gymnosperm seeds (Old and others, 1987;originally identified as ‘Strophalosta’, Howell, 1859, p.32), cannot becertainly located. The Old Series one-inch field slips have "fossils" marked at Ash Green [SP 335 839] and at Neal's Green [SP 337 844], but both localities are now built over.

Sections at Websters, Hemming and Sons Ltd Brickworks [SP 342 806], which expose beds about 200 m above the base of the Formation, show rapid variations between mudstone and sandstone. In the following composite section [SP 3419 8072] to [SP 3416 8058] all the beds are red-brown unless otherwise stated:

The active workings in 1988 [SP 343 805] exposed beds corresponding to those above the 3.8 m sandstone in the section just detailed. Here, however, there is a preponderance of mudstone in the sequence, and the sandstone beds are generally less than 1 m thick. Individual sandstones are very variable in thickness, with the greatest variation displayed in east–west faces, suggesting that currents were perpendicular in direction. Load casts occur abundantly below and within many of the sandstones, and some sandstones show parting lineations or in-fill mud cracks.

Besly (1988, p.213) figures a section of this pit, and concludes that the beds represent ‘an alluvial sequence in which most of the discharge was concentrated in large flood events’.

Vernon (1912), and Eastwood and others (1923) both recorded Walchia here. This identification was corrected by Florin (quoted in Wagner 1983) to Lebachia piniformis, and he also identified L. frondosa var.zeilleri and Ernestiodendron filiciforme here.

The pit was notified as an SSSI in 1986, but unfortunately planning permission had already been granted for restoration. ‘Coventry City Council, as local planning authority, decided that the pressing local need for sports pitches and public open space outweighed the national importance of the SSSI and have decided to completely infill the pit’ (Nature Conservancy Council, 1988 p.33).

The remaining part of this sequence, up to the base of the Corley Member, is mainly obscurred by drift or buildings and it has been left largely undivided.

Vernon (1912) recorded Calamites sp. at a depth of 120 ft (36.6 m) in the Whitmore Park Borehole.

Corley Member

The Corley Member consists of about 85 m of coarse, characteristically pebbly sandstone, and minor mudstone and conglomerate. These beds were termed ‘Corley Conglomerates and Sandstones’ by Eastwood and others (1923), but unfortunately they also used the term ‘Corley Conglomerate’ which has been perpetuated by later writers (e.g. Shotton, 1929; Old and others, 1987). Because the proportion of conglomerate in these beds is always small the latter ascription is inappropriate, and they are here named the Corley Member.

The Corley Member can be traced right across the area between Burrow Hill [SP 305 849] and Sandy Lane [SP 332 802]. Its component sandstones form strong features particularly in the north, and in the agricultural areas soils derived from these beds are seen to be very pebbly.

In a lane at Burrow Hill [SP 3062 8499] 2 m of very weathered conglomerate are exposed. The pebbles are mainly rounded, up to 10 cm in diameter, and comprised of a variety of sandstones, quartzites and chert. Shotton (1927 p.673; localities 25 to 30) gives the following pebble count for this area: Valentian (Silurian) sandstone 73%, Quartzite 7%, Vein quartz 2%, others 4%. Limestone is notable by its absence.

Conglomerate can be traced for 450 m along the ridge south-south-east from Burrow Hill. The same bed crops out in fields 200 m to the south-west on the opposite limb of a shallow syncline.

Flaggy, red-brown, cross-bedded sandstone, with rare pebbles, is exposed to 3 m in a quarry at Bennett's Road [SP 3187 8280].

A well at Brownshill Green Pumping Station [SP 3063 8270], starting near the top of the Corley Member, penetrated sandstone with thin mudstones to 65.5 m, including 10 m of conglomeratic sandstone at 46.0 m.

Sections near Radford Road, described by Eastwood and others (1923, p.86), are now limited to exposures on the north side of the railway cutting for 150 m south-west of Sandy Lane [SP 3311 8020]. Here up to 5 m of cross-bedded, coarse sandstone is channelled for at least 3 m by the sandstone above. The upper sandstone has a 15 cm pebbly basal lag, containing ironstone and mudstone clasts up to 3 cm in diameter. Cross-bedding in the lower unit has dips towards 236° and 10°, while in the upper unit it dips towards 6°.

Beds above the Corley Member

These beds, which consist mainly of sandstone with a few persistent mudstones, form well-developed dip and scarp features between Allesley Park [SP 302 802] and the Jaguar Works [SP 302 820]. A quarry at Church Farm [SP 3036 8125] exposes the following section of red-brown beds:

Weathered, flaggy, cross-bedded sandstone, dipping south at 4° is exposed in 3 m high banks along Staircase Lane [SP 3018 8115].

Small exposures in Allesley, at Butcher's Lane [SP 3002 8082] and Birmingham Road [SP 3013 8061], are of pebbly sandstone and channel lag conglomerate. These are the ‘Allesley Conglomerates’ of Eastwood and others (1923) and later writers, but they appear to be a local development with little value for stratigraphical correlation. Shotton (1927, p.613) gives the following pebble counts for these localities respectively: Valentian sandstone 26%, 20%; Quartzite 0%, 19%; Vein quartz 1%, 0%; Chert 12%, 10%; Limestone 50%, 39%; others 10%, 12%, as well as many marl pellets.

The Birmingham Road locality is notable for the occurrence of large, prostrate trunks of silicified wood (Buckland, 1836; Eastwood and others, 1923). These are referred to as Dadoxylon by Vernon (1912) and Cordattes brandlingt by Eastwood and others (1923).

Triassic

Bromsgrove Sandstone Formation

About 5 m of Bromsgrove Sandstone occur in a small outcrop, which unconformably overlies the Coventry Sandstone in the extreme southeast of the area. Small exposures of pale buff sandstone and red mudstone occur in the railway cutting south of Mercer Avenue [SP 3499 8060].

Structure

Pre-Westphalian structures

Viewed in their regional setting (Old and others, 1987 fig. 2) the Cambrian rocks lie on the north-west limb of a broad NE-SW syncline, which has been identified by plotting the faunal zones proved in boreholes. Dip azimuths from dip-meter logs of the Brownshill Green and Staircase Lane boreholes (5 to 15° at S20°W and 5 to 100 at S10°E respectively) are consistent with this structure. No other dip-meter logs have been examined; but dips measured on borehole cores fall within the range 50 to 20°. Folding in the Cambrian rocks presumably dates from the Caledonian orogeny.

Post-Caledonian - Pre-Triassic structures

The structures within the Carboniferous rocks are shown in Figure 5. The beds lie on the eastern limb of the Warwickshire Coalfield syncline (Mitchell, 1942) and dip gently to the south-west or south. Faults and minor folds trend mainly NNW-SSE or N-S, with minor NE-SW faults. In detail the structures at the level of the Two Yard differ from those at the surface. The Keresley Reverse Fault, with a maximum easterly downthrow. of 27 m, has been proved in mine workings and by seismic surveys. No displacement was detected at the surface, but gentle folding occurs parallel to the northern part of the fault, and surface faults with a parallel trend occur to the southeast. The gentle folds proved in the Two Yard near Coventry Colliery do not appear at the surface.

The structures in the Two Yard which are not apparent at the surface may have originated during intra-Westphalian movements which led regionally to an unconformity at the base of the Halesowen Formation (Old and others, 1987). Those which post-date the Enville Group are probably contemporaneous with the pre-Triassic movements which led to the major unconformity at the base of the Bromsgrove Sandstone.

Post-Triassic structures

Because the Bromsgrove Sandstone is very poorly exposed its structure is unknown. Regionally, however, it dips very gently south-east (Bridge 1988).

The NW-SE fault at Coundon is known to have a post-Triassic throw in the area to the south (Old, 1988).

Quaternary

The older Quaternary deposits are the product of the Wolstonian glacial stage, although they do not occur in a readily identifiable stratigraphic sequence of characteristic lithologies like that found in the type-Wolstonian area to the south-east (Shotton, 1953). The glacial drift was deposited on a bedrock surface rising to the west, and without major rockhead depressions (Figure 6).

Boulder Clay (Till)

Boulder clay forms the bulk of the glacial deposits, and occurs as extensive remnants of what was probably a continuous drift plateau (Figure 6). In the agricultural areas the boulder clay gives rise to heavy clay soils with abundant "Bunter" quartzite pebbles, and scattered blocks of angular quartzite probably derived from outcrop of the Cambrian Hartshill Quartzite 10 km to the north-north-east.

At Coventry Colliery excavations for new coal plant [SP 3203 8443] revealed:

Excavations for lagoons at Coventry Colliery [SP 3232 8420] did not encounter any chalky till but showed:

Sand and Gravel

No clear relationship between the sand and gravel bodies and boulder clay could be established, but it is probable that the sand beds described above thicken sufficiently in places to be mapped.

In a sand pit south of Exhall Grange School [SP 3350 8390] Eastwood recorded (MS field map):

‘8 ft (2.4 m) sand varying from almost white to red-brown, the latter cemented into sand-rock. Occasional lenticles of pale clay; lenticles and pockets of gravel, usually fine; in parts entirely of small flints, in others small Bunters. Nuneaton (Cambrian) rocks rare. Top part clayey in pockets with larger pods’.

Sand and gravel crops out along the eastern margin of the area at Little Heath [SP 348 825], and boreholes along Foleshill Road have proved thicknesses of up to 5 m.

The county series 6-inch sheet Warwickshire 21NE shows what appear to be shallow pits at ‘Webster's Sidings’; in Narrow Lane (now Kingfield Road), which crosses these pits [SP 3353 8088], Eastwood (MS field map) recorded 4 ft (1.2 m) of sand and gravel with rounded Bunter quartzite and vein-quartz pebbles, and angular clasts of Hartshill Quartzite, diorite and Stockingford Shale.

Glaciolacustrine Clay

A small outcrop of glaciolacustrine clay underlies playing fields at Wheelright Lane [SP 3350 8382]. Soft, red-brown, laminated clay was augered here.

Laminated clay, silt and sand was augered in a few localities within the boulder clay outcrop between Edgewick Park [SP 346 815] and Paradise [SP 368 808], but it was not possible to delineate any outcrops.

Alluvium

Alluvial flood plains, rarely over 100 m wide, border the main streams. An upper layer of red-brown sandy loam about 1 m thick is underlain by gravelly alluvium. Boreholes along the River Sowe north of Barratt's Farm [SP 342 846] proved alluvium up to 3.2 m thick. In the built-up areas the outcrops of alluvium are taken mainly from the earlier six-inch survey.

Made Ground

Made ground has been mapped only where it forms topographic features with clearly defined boundaries. In addition, much of the industrialised south-east quadrant of the area is heavily disturbed to a depth of several metres, and covered with a mixture of building rubble and fill.

The made ground at Coventry Colliery [SP 320 839] and west of Wheelright Lane [SP 330 839] is mainly colliery spoil; at Longford [SP 347 834] it may include ash from the former gas works; elsewhere it is probably a mixture of ash, building rubble and locally excavated bed-rock and drift.

Economic geology

Brick clay

Bricks were formerly made from Keele Formation beds dug at Foleshill Brickworks (see p.12). A short-lived pit in the Keele Formation at Wilson's Lane [SP 349 847], shown to have been up to 9 m deep on undated plans in the Warwickshire County Council archive, was probably worked for brick clay. Both pits are now completely restored.

Beds from the lower part of the Coventry Sandstone are still exploited at Websters, Hemming and Sons Ltd. Midland Brickworks, Stoney Stanton Road (see p.15).Mudstone in the Coventry Sandstone above the Corley Member was formerly worked in a shallow pit west of Barker's Butts Lane [SP 322 801].

Building stone

Sandstone from the Coventry Sandstone was formerly worked, probably for building stone, at Church Farm, Allesley (see p.18).

Coal

The only coal seam of economic importance, the Thick Coal, is currently mined at Coventry Colliery, and workings from the former Exhall and Newdigate collieries occur east of Neal's Green [SP 335 849] and north of Woodshires Green [SP 345 845]. Seam nomenclature published by the National Coal Board (1985) shows that the current workings lie mainly within the area of Prime Thick Coal, while the older workings lay mainly within the area of Splitting Thick Coal. Some analytical data and seam sections for the Bench, Seven Feet and Two Yard seams are published (National Coal Board, 1957).

Sand and gravel

Glacial sand and gravel has been worked on a small scale west of Wheelright Lane and at Webster's Sidings. There are no economic. resources within the area.

Water supply

Wells currently in use are shown in (Table 1); actual abstraction rates for industrial wells are confidential.

(Table 3) Water abstraction data for major licenced wells in 1984. (Source: Severn-Trent Water Authority, 1986). CS = Coventry Sandstone, KF = Keele Formation, Ml/d = megalitres per day (1 Ml/d = 9164 gallons per hour).

Further information about wells, past and present, including water analyses is given by Anon (1950), Butler (1944), Eastwood and others (1923), Lyon (1949) and Richardson (1928).

References

ANON. 1950. Coventry Corporation Water Undertaking. Journal of the Institute of Water Engineers, Vol.4, 335–347.

BESLY, B M. 1988. Palaeogeographic implications of late Westphalian to early Permian red-beds, Central England. 200–221 in Sedimentation in a synorogenic basin complex. B M Besly and G Kelling (eds.). (Glasgow and London: Blackie.)

BRIDGE, D Mc C. 1988. Geological notes and local details for 1:10 000 sheets: SP38SE (Coventry North-East). (Keyworth: British Geological Survey.) ,

BRIDGE, D McC. 1989. Geological notes and local details for 1:10 000 sheets:SP38SW (Bedworth West). British Geological Survey Technical Report WA/89/24.

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Appendix. Schedule of boreholes for SP38SW

Detailed logs of non-confidential boreholes may be examined at the BGS National Geosciences Data Centre, Keyworth, by prior appointment, and on payment of the current fee. c Denotes confidential record, details of which may only be released by permission of the original source.

Figures and tables

View original figures in PDF

Figures

(Figure 1) Area of this report relative to area of whole contract is shown with bold outline

(Figure 2) Comparative Westphalian successions in cored borehole

(Figure 3) Comparative Halesowen Formation successions

(Figure 4) Comparative borehole sections in Coventry Sandstone

(Figure 5) Structure of the Carboniferous Rocks

(Figure 6) Rockhead elevation at the base of the drift and thickness of drift

Tables

(Table 3) Water abstraction data for major licenced wells in 1984. (Source: Severn-Trent Water Authority, 1986). CS = Coventry Sandstone, KF = Keele Formation, Ml/d = megalitres per day (1 Ml/d = 9164 gallons per hour).