640 THE COLLIERY GUARDIAN. March 28, 1913. are arranged in descending order, and a correlation of these seams is suggested:— South. North. "Two-Yard coal .... Four-Feet coal. Warwickshire Thick coal. Ryder coal Bare coal Ell coal Ryder coal. Bare coal. [Slate coal Slate coal. Seven-Feet coal.... Seven-Feet coal. — Double coal. — Bench coal. The Seven-Feet coal appears to be the only seam which has been recognised individually throughout the coalfield. The Double and Bench coals are not known in the extreme south of the coalfield; and in the extreme north, near Tamwortb, it becomes impossible to identify the Ryder, Bare, and Slate coals. The measures above the Seven-feet coal show a progressive thinning from the north to the south of the district; this is accompanied by a tendency of the seams to come together, until, south of Bedworth, the Two-yard, Ryder, Bare, Ell and slate coals unite to form the Warwickshire Thick coal. This phenomenon is a striking illustration of the effects of an unequal rate of sedimentation indifferent parts of the basin of deposition, the ultimate cause being a differential movement in the area. The outcrop of these coalseams can readily be made out over a large portion of the northern area by following the lines of old workings. Above the Thick coal there are about 300 ft. of strata which, on palseobotanical evidence, must be placed in the Middle coal measures. These rocks, which include the Forty-feet sandstone, consist of extremely variable beds of strongly current-bedded sandstones and shales, with one or two thin coals, some fireclays, and certain peculiar breccias. The outcrop of this subdivision consists of two narrow arms, which meet in the north of the coalfield. From the identity of the seams which form this double outcrop, it is evident that the coal measures lie in a broad, shallow syncline pitching towards the south, and having its longer axis in a north-and-south direc- tion. The strata dip steeply away from the eastern, northern and a portion of the western boundary; but, towards the centre of the basin, they become almost horizontal. South of Polesworth, and east of the coal outcrops, a subsidiary anticline causes the measures to roll over and dip eastwards into the boundary fault. There is evidence of a similar faulted anticline beneath the trias at Brandon, in the south. The greater part of the syncline is concealed from view by the spread of upper coal measures, permian and trias, which come on successively towards the south. The most striking and characteristic feature of the Keele beds is the occurrence therein of Spirorbis lime- stones. A thin bed of limestone containing Spirorbis has long been known to occur in the Warwickshire coal- field ; and, by means of the numerous old workings in it, Mr. H. H. Howell was able, 50 years ago, to lay down the line of outcrop on the Geological Survey maps. The position of this bed was supposed to be in the pro- ductive coal measures at about 50 ft. below the base of the permian rocks. As the true relationship of the carboniferous to the permian was not at that time fully understood, there was a tendency to refer every exposure of limestone to the outcrop of one bed, and the finding of Spirorbis therein was regarded as sufficient confirma- tion of that opinion. It has since been pointed out by the late Mr. 0. Fox-Strangways that, near Baxterley, there are apparently two beds of limestone ; but it is not certain whether this double outcrop is caused by two distinct beds, or whether it is to be regarded as a repetition of the same bed by a fault or roll of the strata. Mr. Howell’s statement as to the occurrence of a limestone near the Hall, Nether Whitacre, has recently been con- firmed by Mr. T. C. Cantrill, who has also detected another isolated exposure of limestone, 5 miles farther south, at Maxstoke. Both these outcrops are by that author considered to be, not in the coal measures, but in the permian. During the re-survey for the purpose of this paper, conclusive evidence has been obtained to show that there are in the Upper coal measures of this area, not merely a single bed of limestone, but many different beds distributed throughout about 1,500 ft. of strata. Although these beds are so thin, being often only a few inches thick, and rarely exceeding 3 ft., four of them are somewhat persistent; but all are constant in lithological and palaeontological characteristics. A diligent examination of other beds (particularly the thin upper bed) has failed to reveal a single fossil. Indeed, there is reason to believe that some of these limestones are, in part, of inorganic origin, and that their formation may be largely the result of chemical precipitation. Most of the Spirorbis limestones, whether in the Nuneaton clays, in the Haunch wood sandstones, or in the Keele beds, are merely impersistent lenticular bands. Within the basin this Spirorbis limestone has been proved in the following colliery-shafts and boreholes:— Depths in feet. Exhall Colliery, near Bed worth.................. 340 Well-section near the Griff Clara Colliery, Nuneaton 60 Tunnel Colliery, Stockingford.................... 286 Baddesley Colliery (Stratford Pit)............... 148 New sinking at Biddles Wood, near Kingsbury ..... 250 Whitmore-Park Boring, near Coventry............. 1,637 Keresley Boring................................ 1,413 It is shown that more than half of the area of the so-called “ permian ” must be relegated to the carboni- ferous ; the remaining portion of these rocks (the Corley conglomerates and the Kenilworth sandstones) are next considered. Until definite palaeontological evidence to the contrary is forthcoming, the Corley conglomerates must be regarded as of permian age, as must also the Kenil- worth sandstones, owing to the abundance of Walchia imbricata, a typical permian plant. The permian was said to dip at about 15 degs., while the Lower Keuper was nearly horizontal. Still farther south the latter rests upon higher horizons of the permian until Warwick is reached. The unconformity between the trias and the palaeozoic rocks is thus one of the most conspicuous features in the geology of Warwickshire. The following table embodies an account of the more important sinkings and borings in the southern part of the coalfield. It has been added in order to illustrate the geological structure of that part of the district:— Important Sinkings and Borings in the Warwickshire Coalfield. Locality of 5 boring. ftg Thicknessin feet. Spring Pools ..... 370 ... 2,009 ...Coal measures to 2,009 Keresley ......... 445 ... 2,173 ...Coal measures to 2,173 Whitmore Park..... 340 ... 2,591 { meases ijsi Foleshill ........ 310 ... 1,055 {^“eds"'.'.i SponEnd........... 266... 575 { FSXds . 385 Whitley........... 230 ... 250 Tile Hill ........ 350... 693 ... Permian to. 693 Kenilworth . 237 .. 226|... Permian to 226i Leamington — 346|... U pper keuper to 3461 f Upper keuper 60 Stoke . 240 .. 169 ■< Lower keuper 82 t? Keele beds ... 27 f Drift 21 Brandon . 270 .. 366? j Keuper 313 (. Coal measures 32 Weston . 360 .. 300 ...Upperkeuperto 300 Burton Hastings . 330 .. i on ( Lo wer keuper... idU (Cambrian 60 70 C Drift 27 Nuneaton . 210 .. 123 Lowerkeuper... 81 Bedworth Charity Colliery . 360 .. t Cambrian 1 029 J Coal measures ’ ( Cambrian 15 795 234 • Lindley . 300 .. 660 ...Keuper to 660 The structure of the coalfield is remarkably simple, especially in the northern portion, where the various subdivisions of the coal measures, and also the coalseams, crop out symmetrically on each side of the syncline. In the south this symmetry is partly hidden by the pitch of the syncline, and by the unconformable cover of permian and trias, and partly destroyed by the western boundary fault. Table Illustrating the Correlation of the Coalfields of the Midland Province. North Staffordshire. Nottinghamshire. Leicestershire. South Staffordshire. Warwickshire. Cover: Trias. Permian magnesian limestone. Salopian permian. Salopian permian. Salopian permian. Avonian Subdivisions of the series. Westphalian series. Keele beds. + 700 ft. Newcastle beds. 300-350 ft. Etruria marls. 800-1,100 ft. Blackband group. 300 450 ft. Middle coal measures. 4,000 ft. Lower coal measures. 1,200 ft. Millstone grits. Limestone shales and Carboniferous Limestone. Keele beds. + 188 ft. Newcastle beds. 91ft. Etruria marls. 283 ft. Absent. Middle coal measures. 2,000 ft. Lower coal measures. 1,000 ft. Millstone grits. 1,300 ft. Limestone shales and Carboniferous Limestone. Absent. Absent. Absent. Absent. Middle coal measures. + 1,600 ft. Lower coal measures. (?) 1,000 ft. Millstone grits. 50 ft. Limestone shales and Carboniferous Limestone. Keele beds. + 800 ft. Newcastle beds. 500 ft. Etruria marls. 600 to 1,000 feet. Absent. Middle coal measures. 500 to 2,000 feet in the north. Absent (except in the north). Absent (.except in the north). Absent (except in the north). Keele beds. 1,600 ft. Haunchwood sandstones. 300 ft. Nuneaton clays. 100 ft. Absent. Middle coal measures. 400 to 700 feet in the north. Absent. Absent. Absent. Floor: (?) (?) Pre-Cambrian. Silurian. Cambrian. The proved faults within the coalfield are neither very great nor very numerous; but the western and eastern boundary faults are important dislocations. The eastern boundary of the palaeozoic rocks is, in part, a fault which runs in a south-easterly direction from Shuttington by Polesworth and Atherstone to near Nuneaton. The amount of throw is unknown, but it decreases southwards and at Nuneaton, where the junction between the trias and the older rocks is an unconformity and the fault is entirely in trias, the displacement is probably quite small. On the upthrow side of the fault the Cambrian has been proved beneath the lower keuper at the White Stone, Burton Hastings and at. Nuneaton. On the downthrow side a boring at Lindley has penetrated more than 600 ft. of keuper without reaching the base of the subdivision. Near Market Bosworth, 7 miles north-east of Nuneaton, a series of borings passed through the trias into the Cambrian ; and Mr. Horace Brown has shown that this part of the palaeozoic floor forms a sub-triassic anticline parallel with the Nuneaton ridge. The western and north-western boundary fault is probably the most important one; but at present there is no means of estimating the displacement, as the thickness of the strata is unknown. On this point the only evidence available is the King’s Heath boring, near Birmingham, which ended in keuper rocks at a depth of 1,106 ft.; also a boring farther north at Streetly, which proved about 1,850ft. of red “permian” sand- stones, marls, and conglomerates of unknown age beneath 50 ft. of hunter pebble beds. South of the district, at Stratford-on-Avon, the base of the keuper has not been reached at a depth of 800 ft. Nothing very definite can thus be affirmed concerning the southern portion of the county. With regard to the age of the movements which have affected the coalfield, it is obvious that the main folding and faulting took place after the deposition of the Upper coal measures and before the trias was laid down; but* whether it is of pre- or of post-permian age is not so clear. The permian has been proved unconformable to the Keele beds, and so it is probable that the main folding was pre-permian; but there has been subsequent upward movement of the old palaeozoic ridges along the same lines in post-permian and also in post-triassic times. The coal* measures of Warwickshire are merely the remnants of an extensive sheet which formerly over- spread a wide area in the Midlands. With other existing portions of this sheet it is possible to institute a close comparison. In other words, the stratigraphica succession, lithological characters, and fossil contents of the coal measures of Warwickshire can be correlated with those of the other coalfields of the Midland counties, and more especially does this apply to the South Staffordshire coalfield. Such a correlation is indicated in the appended table. In this connection, it may be remarked that it is still a matter for speculation whether Upper coal measures were ever deposited over the Leicestershire area; but this does not affect the question of the correlation of the Middle coal measures. The Middle coal measures of Leicestershire are very similar to those of Warwick- shire, and the resemblance extends even to minor points, such as the occurrence of certain coarse grits towards the summit of the group near Polesworth in Warwickshire, and also near Moira and Boothorpe in Leicestershire. One striking feature, which each of these coalfields has in common with the South Stafford- shire coalfield, is the occurrence of seams of coal of exceptional thickness formed by the union of several individual seams. From this and other evidence it appears extremely probable that these separate areas of coal measures were formed under similar conditions in one general basin of deposition. In North Staffordshire and in Nottinghamshire the Keele beds are not fully developed, and the summit of