Clee Hills Research Articles

John Robert Lawrence Allen. 25 October 1932—18 October 2020

John Allen was one of the leading British geologists of the late twentieth century, who changed his primary research focus in mid career from clastic sedimentology to geoarchaeology. He read for a BSc degree in geology at the University of Sheffield, graduating with first class honours in 1955. He continued at Sheffield as a postgraduate student researching the geology of the Old Red Sandstone of the Clee Hills in Shropshire, but never submitted a PhD thesis. However, in 1958 the University of Reading offered him a research fellowship to investigate the geology of the hydrocarbon-rich River Niger delta region. In 1961 he became a lecturer in geology and a member of the new purpose-built Sedimentology Research Laboratory at Reading. The international renown of the laboratory was largely based on his prodigious sedimentological research output relating to sedimentary structures, river and coastal environments and Devonian continental deposits. He was appointed reader in 1967 and professor in 1972. In 1974 he led the founding of a taught MSc course in ‘Sedimentology and its applications’, which soon became a world leader. In 1988, in the context of the rationalization of university geology departments, Reading's department was selected for closure. However, John Allen's research esteem was such that a special case was made and a postgraduate-only institute specializing in sedimentology was established with him as director. He resigned the directorship after five years in favour of a research professorship. His objectives changed from orthodox old-rock studies to research on recent muddy estuarine sediments. By selecting the estuary of the River Severn as his new field area, he soon realized that this opened up a rich area of collaboration with colleagues in archaeology. His geological skills were subsequently applied to a range of archaeological problems. He became a key contributor to a new MSc degree course in geoarchaeology.

Opencast coal mining: a unique opportunity for Clee Hill Quarry

Abstract Clee Hill Quarry is an active hardstone (dolerite) quarry located 5 miles to the east of Ludlow, Shropshire. The quarry is in Carboniferous Coal Measures which have been intruded by a thick ( c. 60m) conformable fine-grained olivine-dolerite sill. The whole sequence is now folded into a broad synclinal structure and is extensively faulted. The area is blanketed by glacial deposits, 2–12m thick. Historically, quarrying operations have been closely allied to the geological structure being confined to the margins of the syncline where the dolerite is devoid of overlying Coal Measures. In 1973 a programme was undertaken to assess the viability of using Coal Measures material for the production of lightweight aggregate. This programme was initiated because virtually all remaining, albeit substantial, planned reserves of dolerite were overlain by considerable thicknesses of Coal Measures and glacial deposits. While initial results from a technical viewpoint were encouraging, the project was abandoned for commercial reasons. The Coal Measures sequence overlying the dolerite sill comprises in excess of 30 m of mudstones, siltstones and sandstones as well as four recognized coal seams. Piecemeal mining of this coal had taken place on the Clee Hills for centuries, and in the area for future quarrying abundant evidence was available at surface of former bell-pit workings. In the early 1980s a decision was taken to evaluate the coal deposits at Clee Hill Quarry. The area for detailed assessment was defined using existing borehole data and evidence from old workings identified from site survey and aerial photographs. Exploration in two separate phases comprised the drilling of 44 open holes with spot coring and borehole geophysical logging. Coal quality was determined by analysing all relevant borehole core samples. Although coal reserve estimates assumed a high degree of past shallow mining activity, the economic viability of working the coal seams by opencast methods was established. In 1986 a planning application was submitted to Shropshire County Council to work and remove all coal overlying the dolerite, over a 3 year period. The proposal would allow exploitation of a valuable mineral asset, release substantial reserves of hardstone (dolerite) and allow restoration at an early date of large areas of former mining and quarrying dereliction. Planning permission was obtained in August 1988. Negotiations with the Opencast Executive of British Coal culminated in the granting of a licence to work both British Coal (vested) and ARC (alienated) coal. Coal mining was commenced in October 1988. Predictions of seam thickness and faulting were consistently accurate and vindicated the site investigation programme. In two aspects more detailed/accurate information would have been useful. Firstly, with regard to coal quality, borehole core samples did not accurately reflect in situ moisture content. Secondly, the extent of old workings in the upper coal seams was significantly overestimated. Neither aspect significantly affected the viability of the project. The mining phase including the major restoration works was completed in July 1992.

Palynological evidence for an early Namurian age of the Cornbrook Sandstone Formation, Clee Hill, Shropshire

SUMMARY The formational name Cornbrook Sandstone has been applied to a variable succession of conglomerates and coarse-grained sandstones, with thin mudstone and coal intercalations, which occurs between the Carboniferous Limestone (Dinantian) and Coal Measures (Westphalian) in the Clee Hills area of Shropshire. Previous biostratigraphical investigations have proved inconclusive, suggested ages ranging from Tournaisian to Westphalian B. Palynological investigations on material from surface exposures and from three cored shallow boreholes, which penetrated most of the Cornbrook Sandstone sequence together with part of the underlying Carboniferous Limestone, provide new evidence for the age of the formation. Well preserved miospore assemblages indicate an early Namurian (Pendleian-Arnsbergian) age. The palynological evidence suggests that the base of the Cornbrook Sandstone is younger than the base of the Drybrook Sandstone of Gloucestershire, which exhibits broad similarities in tectonic and depositional settings. The two sandstones may, therefore, represent unrelated sand bodies, located north and south of St George’s Land. Alternatively, if they represent remnants of a more extensive deposit, its base may have been diachronous, becoming younger to the north.

Sedimentology of the Old Red Sandstone (Siluro-Devonian) in the Clee Hills area, Shropshire, England

The sequence of approximately 1300 m is divided by a major unconformity (Middle Devonian) into the thick Lower Old Red Sandstone (Siluro-Devonian), resting disconformably on Ludlovian (Silurian) marine strata, and the much thinner Upper Old Red Sandstone (Upper Devonian) overlain by the Carboniferous. The Lower Old Red Sandstone commences with littoral sediments (Downton Castle Formation) followed by tidal mud-flat deposits (Temeside Formation) formed after a brief marine transgression. The predominant remainder of the sequence (Ledbury Formation, Ditton Group, Abdon Group, Woodbank Group), characterized by fining-upwards cyclothems, records the establishment during a marine regression of extensive and persistent alluvial plains. Prior to Ditton Group times, detritus came from relatively distant regionally metamorphosed rocks lying to the north or west of the Clee Hills. Subsequently, apparently as the result of river-capture or drainage-reversal consequent on the commencement of the final (mid-Devonian) phase of Caledonian movement, high-level crustal rocks closer at hand (largely Wales) replaced the metamorphics as the sources of sediment, the earlier Lower Old Red Sandstone itself being recycled. To judge from the calcretes preserved in the alluvial formations, the area lay near the Equator and experienced a relatively dry hot climate. The Upper Old Red Sandstone likewise reveals fining-upwards cyclothems. The overlying Carboniferous rocks evidence the renewed marine transgression of the area, after the removal of the effects of the mid-Devonian movements.

A Field Test of Palaeomagnetic Stability

Summary A field test of palaeomagnetic stability is described, based on a comparison of the magnetizations in mineralogically identical baked and unbaked sedimentary rocks. If successful, the test demonstrates the stability of the magnetization acquired during baking. Two instances are given of its actual application, one of which has led to a re-interpretation of the palaeomagnetism of certain Carboniferous formations. The test is compared with the three main field tests in common use. This is an account of a new field test for the stability of magnetic directions in ancient rocks, which may supplement the three field tests already in use. The new test is based upon measurements on baked rocks. Many years ago, Brunhes (1906) pointed out that if the magnetic directions in associated baked and igneous rocks agreed, they could probably be regarded as stable. Our work is essentially an extension of this idea, for which measurements are made not only on the baked rock but also on neighbouring unbaked material. As a result one can eliminate the main weakness of Brunhes test, which is that occasionally both baked and igneous material can become simultaneously remagnetized after cooling by regional metamorphism. It will be most convenient to describe the test by means of two concrete examples: the first occurring in material associated with a Tertiary dyke, 40-50 million years old, from Port-na-Traigh-Linnhe near Oban, Argyllshire ; and the second in materi'al associated with the Carboniferous sill about 250 million years old that forms the Clee Hills in Shropshire. 2. The Tertiary dyke The Tertiary dyke at Port-na-Traigh-Linnhe is about ten feet wide, running north-west and practically vertical through a stretch of compact red mudstones of Devonian age. The mean tilt of the mudstones is 11' down at 200° E. Measurements of the intensity, direction and scatter of the natural remanence, and of the intensity of saturation remanence, were carried out both on the dyke and on samples of mudstone at different distances from the contact. These data, together with sampling details, are presented in Table I. The values of scatter, derived from a formula due to Wilson (1959), represent the standard deviation between individual disks I# in. diameter, $in. thick.

Sandstone-Plugged Pipes in the Lower Old Red Sandstone of Shropshire, England

ABSTRACT Red sandstones and siltstones of the fluviatile Ditton Series (Lower Old Red Sandstone) are pierced at many localities in the Clee Hills by sandstone-plugged pipes lying nearly normal to the bedding. These cylinders are long and narrow and sharply cut depositional structures of the host beds. The cylinders often carry siltstone fragments and sometimes course horizontally for long distances beneath siltstone layers before rising into higher beds. The less steeply inclined plugged pipes are usually associated with lateral structures formed of alternate, arcuate bands of fine siltstone conglomerate and sandstone. At one locality the cylinders rise from a convolute bedded sandstone. The sandstone cylinders are thought to have resulted from the plugging of tubular ducts eroded by groundwater rising through unconsolidated deposits to reach the depositional surface. The lateral structures seem to indicate the migration of the loci of erosion. The Lower Old Red Sandstone plugged pipes belong to a class of structures which includes sand and mud volcanoes, spring pits, and certain cylindrical structures described from other sandstones.

Rock Magnetism and the Origin of the Midland Basalts

Summary There has been considerable dispute about the origin of the series of Carboniferous igneous formations in the neighbourhood of the Clee Hills, Shropshire. Palaeomagnetic measurements suggest that all the formations except one are intrusive. They also indicate that the accepted geological interpretation of one formation may require revision.

The Old Red Sandstone of the Cleobury Mortimer Area, Shropshire

The Lower Old Red Sandstone sequence in the area of the Cleobury Mortimer syncline is closely comparable with that in Corvedale. The ‘Holdgate Sandstones’ are recognised and it is shown that individual ‘ Psammosteus’ Limestones can locally be more accurately mapped by geophysical (resistivity) methods. White's ostracoderm zones are recognised and the unfossiliferous Breconian Clee Series is probably present. No Upper Old Red Sandstone has been detected. The relationship of the syncline to the structure of the Clee Hills is briefly considered.

Notes on the Old Red Sandstone of the Clee Hills

The stratigraphy of the Old Red Sandstone of the Clee Hills is described, and a brief account of the palaeontology is given. Within the Lower Old Red Sandstone, the subdivisions Downton Series, Ditton Series and Clee Series are recognised. The Clee Series rest conformably on the Ditton Series, and may be equivalent in part to the Senni Beds. The Upper Old Red Sandstone is represented by the Farlow Sandstones Series.

The results of a gravity survey in the country between the Clee Hills and Nuneaton

Summary Gravity observations have been made in te country between the Clee Hills and Nuneaton. It is found that the change of anomaly over the Warwickshire Coalfield is closely correlated with the thickness of Coal Measures, and over the Forest of Arden it is less closely correlated with the thickness of Trias. The corresponding differences of density agree with densities of rocks measured at the surface. Data are insufficient to establish definite correlations elsewhere. The remaining anomalities indicate a considerable thickness of rather light rocks, probably Coal Measures, amounting to 4000 feet below the Trias in the Forest of Arden and a considerable thickness of Trias, about 2500 feet with perhaps also some Coal Measures, at Kidderminster.

IX. On the fossil floras of the Wyre Forest, with special reference to the geology of the coalfield and its relationships to the neighbouring coal measure areas

In the Western Midlands of England and along the Welsh Borderland a series of coalfields occurs parallel to the course of the River Severn, and, for the most part, situated to the West of that river. The main links in this chain begin in the North with the Shrewsbury coalfield. Next follows the Le Botwood area, then Coalbrookdale and the Wyre Forest. Further still to the South is the little coalfield of Newent in Gloucestershire. This line terminates in the Forest of Dean and Bristol coalfields. In addition, a few detached areas of coal measures, of which the Clee Hills are the most important, lie further to the West. To the North of Shrewsbury, the line is continued by the Denbighshire (Wrexham) and the Flintshire coalfields, both situated for the most part to the West of the Dee. There is little doubt that the coalfields lying along this line, roughly North and South, are not all related to one another, either stratigraphically or tectonically. We are concerned here with the fields beginning with the Shrewsbury and ending with the Newent areas, and more especially with that of the Wyre Forest. We may at once exclude from primary consideration the Forest of Dean and Bristol fields in the South, and the Dee Valley coalfields in the North, as being quite unrelated, at least stratigraphically, to the Wyre Forest.

V.—The Geology of the Titterstone Clee Hills

The following is a preliminary account of the rocks overlying the Lower Old Red Sandstone of the Titterstone Clee Hills, Shrops.

The Permian Conglomerates of the Lower Severn Basin

I. I ntroduction . B etween the River Severn and the village of Enville in South-east Shropshire, and again round the southern half of the South Staffordshire Coalfield, there are certain bands of rocks cemented and hardened by calcareous matter—namely, calcareous conglomerates, cornstones, and calcareous sandstones—which constitute parts of the group classified by the officers of the Geological Survey as Middle Permian. The object of this paper is to trace the materials composing these calcareous rocks to their sources. The typical Permian sequence of the Shropshire type is, according to Prof. Hull, as follows, in descending order:— Murchison stated that at Coton and Bowhills the calcareous horizons of the Middle Permian consist of ‘( a ) coarse conglomerate, composed chiefly of fragments of Carboniferous Limestone, generally rounded ; . . . . some of them are of an oolitic structure . . . . ( b ) conglomerate, with fewer fragments of limestone, but pebbles of quartz, Old Red Sandstone, ere . . . . . and minute fragments of jasper.’ He pointed out that ‘the nearest known masses of similar [Carboniferous\ rock are in the Carboniferous Limestone of the Clee Hills.’ Ramsay collected from conglomerates, included by him in the Middle Permian, at Gatacre Hall and Four Ashes, near Enville, pebbles of He states that ‘the Carboniferous Limestone pebbles by far predominate,’ and that ‘the nearest Carboniferous Limestone is that of the Titterstone Clee :Hills . . . . The Coalbrookdale limestone contains chert . . . . and in the same district occur igneous and

Societies and Academies

LONDON Geologists' Association.—The excursion to Ludlow and the Longmynds on July 22 and five following days, the concluding and most important field meeting of the season, was under the direction of Prof. Morris, F.G.S., Mr. R. Lightbody, F.G.S., and the Rev. J. D. La Touche, B.A. After the members had assembled in Ludlow Castle the Upper Ludlow rocks on the right bank of the Teme were examined, and Mr. Lightbody gave his reasons for considering the Aymestry Limestone to be represented at a point near the old bridge, although Pentamerus Knightii is not found here. The Upper Ludlow contains Chonetes lata in great abundance, and scarcely a fragment of the rock was picked up without this species being seen on the surface. From the high ground by the river side the valley of the Teme may be advantageously seen. The river here flows through a gorge in the Upper Ludlow rocks, with the castle and town of Ludlow picturesquely situated on the left bank; while the “Old Red” country extends beyond to the Clee Hills, the igneous summits of which commandingly rise to the east, surrounded by the coal measures. The well-known section in Ludford Lane, showing the “bone-bed,” was next visited. This bone-bed, or “gingerbread,” as it is sometimes called from its appearance, is in places not more than a quarter of an inch thick, and is found only after careful search. The fragments of the remains of fish, of which it is partly made up, were until comparatively recently the oldest fish remains known. The following day (Tuesday) was devoted to an examination of sections of the Aymestry Limestone, Lower Ludlow, and Wenlock rocks, occurring in the course of a route of about twenty miles. The journey was performed by means of carriages, but abundant occupation was given for the hammers of the party at the various exposures of the richly fossiliferous rocks above named. Graptolites from the Lower Ludlow were obtained in abundance, and fine specimens of Phacops longicaudatus were found in the Wen-lock, exposed in the bed of the Teme, near Burrington; while * Making proper allowance for the precession of the equinoxes,

On the Carboniferous Limestone of Oreton and Farlow, Clee Hills, Shropshire

§ 1. The general physical and palseontological features of the small district referred to in these notes having been carefully and clearly described by Sir Roderick Murchison in his classic work ‘The Silurian System,’ the additional facts which a visit paid to it during the past autumn enables us to record may be considered simply as a continuation of those previously observed. The thin beds of limestone which form the basement of the Titterstone Clee Coal-field are well exposed in a marginal flexure of the strata north-eastward of the hill, at Oreton and Farlow, and also, at a somewhat higher level, around its southern abutments. Our observations upon the character of the beds and their fossil contents have bcen confined to the exposures in the first-named localities. The geographical relations of this limestone ridge with the nearlying millstone-grit and coal-measurcs, in their turn covered up by the sheets of erupted basalt which form the high summits of the Clee, are well scen from the igneous knoll of Kinlet, three miles to the emstward. § 2. Immediately below the summit of the ridge at Farlow, and on the northern side, is a quarry of yellow sandstone, from which recently a large quantity of stone has been obtained for the rebuilding of the church. It is a thick-bedded, fine-grained sandstone, having ripple-marked surfaces, and occasionally containing disseminated pebbles of quartz. The colour of the stone is a pale yellow, in places slightly stained by ferruginous oxidation. Remains of fossil Fishes were first

On The Lower Carboniferous Beds of the Clee Hills

Perhaps in all the physical geology of England there is nothing finer than the erupted heights of the Clee. Encircled by the typical “Old Red”—a wide-stretching tract of alternating sandy shores and gravel-beaches of that period—are the characteristic beds of the coal-measures, lying upon Millstone Grit and Mountain Limestone.Of the causes that have elevated these deposits into the hills of Titterstone and the Brown Clee I need not speak—their basaltic summits, where the erupted rock has assumed a rude columnar form after cooling, are sufficient evidence; but I would direct especial attention to that group of beds whose strike is along the Oreton ridge, and whose chief member, the Mountain Limestone, forms its axial line. This lies midway between the two hills; its southern side slopes down the “Common,” and is composed of Millstone Grit, cut off abruptly by a long line of fault, the effect of which has been to have depressed that deposit into a valley, and to have raised the underlying “Old Red” into a nearly continuous line of cliff. The accompanying section will better describe their relative positions.These Millstone Grits are non-fossiliferous; but the mineralogist may detect in their conglomerated structure many pebbles of a high class, jaspers and cornelians of pure quality being often met with. These beds lead up to the Mountain Limestone, which contains a fine series of organic remains, such as palatal teeth of the Cestraciont fishes. Petalodus Hastingsii and Psammodus porosus are abundant; yet, although fragments of their jaws are not uncommon, I have only met with one specimen having the teeth in their true position.

On the Physical Structure and Succesion of some of the Lower Palæozioc Rocks of North Wales and part of Shropshire

The Sections to which this notice refers are on a scale of 6 inches to a mile, vertically and horizontally. Section No. 1 passes from Mochras Island in Cardigan Bay, over Cader Idris, Radnor Forest, and Hanter Hill, to the Old Red Sandstone near Fern Hall, south of Kington, Herefordshire. It is about 65 miles in length. No. 2 commencing at Llanfair-is-gaer, Menai Straits, passes over Snowdon, Moe]-wyn, Gors-goch (near Trawsfynydd), Aran Mowddwy, and Newtown, Montgomeryshire, and the Upper Silurian rocks and Old Red Sandstone of Clun Forest, Wigmore Valley, &c., near Ludlow. It is 90 miles in length. No. 3 passes across the Shelve and Longmynd country to the Brown Clee Hills*. These Sections were constructed by Messrs. Aveline, Selwyn, Bristow, and Ramsay; and the mapping of the county to which they refer was executed by them and Mr. Jukes. Sections Nos. 1 & 2.—The oldest rocks crossed by Sections Nos. 1 & 2 lie at the base of the Merioneth anticlinal of Professor Sedgwick. They are the Barmouth and Harlech sandstones, which are here and there interstratified with beds of purple slate. Their base is not exposed, and the lowest beds that rise in the centre of the area are from 6000 to 7000 feet beneath the base of the Lingula flags. In places they are pierced by numerous greenstone dykes, a few of which are magnetic. No fossils have heretofore been found in them. These and their equivalents are the rocks coloured as “Cambrian” by the Geological