92 THE COLLIERY GUARDIAN. July 10, 1914. where it is confined to the upper coal measures of the Thurgarton boring.* Next to plants the commonest fossils met with are the shells and casts of lamellibranchs belonging to the genera Carbonicola, Naiadites and Anthracomya. The investigation of their occurrence, however, has not been sufficiently extensive to decide the zonal value of the different species. So far, Carbonicola robusta has been found ranging from the lower coal measures into the middle coal measures, certainly up to the horizon of the Deep Soft coal, but it has not been met with above the Top Hard coal. It also appears that Anthracomya phillipsi, which is abundant at several horizons above the Top Hard coal does not descend below this seam. Thus the distribution of these two fossils agrees with that in adjacent areas.f Of the other organic remains, too little is known of their distribution for their zonal value to be determined. (2.) The occurrence of plants either as isolated frag- ments in the ironstone nodules and in shale, or massed together in the coal, indicates the proximity of land, and possibly, as some geologists' contend in the case of beds of coal, actual land-surfaces on which the vege- tation formerly grew. Nearness to land is also suggested by the presence of Carbonicola, Naiadites and Anthracomya, which are regarded as having lived in fresh water or in estuaries. Since these shells are dis- tributed throughout the sequence, it is evident that much of the sediment accumulated in fresh or brackish water; and, with the exception of the lowest beds of the lower measures, it was long thought that the whole of the coal measures were deposited under these conditions. It was recognised that the shales over the Alton coal (Hard Mine coal of Yorkshire) contained everywhere a marine fauna; but until recently the occurrence of a similar fauna was unknown elsewhere in the middle coal measures on the eastern side of the Pennines, with the exception of two marine shells recorded by Green J high up in the middle coal measures about the Barnsley (Top Hard) coal at two localities in Yorkshire.! In the present area two marine beds have been found in the middle coal measures, one of which occurs between the Deep Soft and Top Hard coal in the Chesterfield district and the other, 740 ft. above the Top Hard coal at Sherwood Colliery. The band below the Top Hard coal has been identified by Dr. Moysey in the Digby clay-pits much further south, in sheet 125; and from the occurrence of marine shells on the spoil-heaps, its presence has been suspected in several other localities, while the bed 740 ft. above the Top Hard coal at Sher- wood has been recognised in several borings and sinkings from near Nottingham city to Thorne, north of Doncaster. § In the Sherwood sinking only a few pieces of shale lying on the spoil-heap were available, and the fossils obtained were not distinctive of the horizon; but at Mansfield Colliery, three miles to the east, where the bed lies 631 ft. above the Top Hard coal, and at Maltby Colliery, where it is 709 ft. above the Barnsley coal, it contains a rich and varied fauna. It may also be stated that several of the goniatites and lamellibranchs are identical with those found in the limestone shales, and a few are carboniferous lime- stone forms. Thus the bed and its fossils indicate an extensive and possibly a prolonged depression which brought back the carboniferous sea, and with it many of the life-forms of the lower carboniferous period. Lower Coal Measures.—This subdivision includes all the measures lying between the first millstone grit and the Silkstone coal. The bold outcrop of the rough rock clearly defines the base, while the Silkstone coal can be traced almost continuously by old crop-workings or by the strong sandstone above the coal. Records of shafts or borings -which would give the complete sequence are wanting; but in the south the thickness of the lower coal measures may be estimated at under 1,200 ft. In the central and northern districts the thickness as calculated from the shaft of Stubbing Edge and from the borings at Linacre and Apperknowle (fig. 3) is 1,200-1,400 ft., while for the southern part of the Yorkshire coalfield, GreenU gives an estimate of 1,650 ft. The horizons most easily recognised and traced are those of the Alton coal, the sandstones of the Wingfield flagstone group and the Mickley coals, of which the relative positions in the sequence of the corresponding horizons of the southern part of the Yorkshire coalfield are shown in the following table :— North Derbyshire. South Yorkshire. Ft. Silkstone Coal. Ft. 200 Measures. Mickley Coals. 450 Measures with irregu- lar sandstones and Kilburn coal in south. Wingfield Flagstones (part). 300-500 Measures with sand- stone and thin coals. Alton Coal. 90-300 Measures with repre- sentative of Soft Bed coal. Measures.............; 200 Whinmoor Coals. Measures including the Penistone flags and Grenoside rock........ 600 Brincliffe Edge Rock. Measures with thin coals and Wharncliffe and Loxley Edge rocks ... 500 Ganister or Hard Bed. Coal. Measures including the Soft Bed coal ...... 300 Rough Rock. While characterised by persistence of the same groups and some of the same individual strata as in *“ Country between Newark and Nottingham,” Mem. Geol. Surv., 1908, p. 16. t “ Southern Part of the Derbyshire, etc., Coalfield,” Mem. Geol. Surv., 1908, pp. 91-100. !“ Yorkshire Coalfield,” Mem. Geol. Surv., 1878, pp. 468- 471. § “ Concealed Yorks-Notts Coalfield,” Mem. Geol. Surv., 1913, pp. 20-23. 11 “ Geology of the Yorkshire Coalfield,” Mem. Geol. Surv., 1878, p. 76. the adjacent district on the south (sheet 125), the lower coal measures exhibit a rather more sandy facies owing to the development of more and stronger beds of sand- stone. This is particularly marked in the measures containing the Alton coal, and in the beds next above the Wingfield flagstones. In the southern part of the coalfield (sheet 125) the measures below those flag- stones consist chiefly of soft strata, usually eroded into a marginal valley, but with two thick sandstones coming in below the Alton coal further north. In the district under description these split and develop into several separate beds, while others appear at lower horizons. Consequently the coal measures here come on above the millstone grit with a series of sandstone escarpments. Moreover, in the northern part of this district a change takes place in the character of many of these rocks. For, while in the south they all exhibit a fine-grained, silty, more or less micaceous, and felspathic, appearance, further north several of them below the Wingfield flagstones develop into sharper and more quartzose sandstones, still as a rule of a fine grain. Occasionally the change of texture has gone so far as to produce beds of coarse-grained and even pebbly quartzose and felspathic grit, undistinguishable from the millstone grits, but of frequent occurrence in the coal measures of South Yorkshire. A bolder and more So/e Hill SCALE Tot ley Moss T. ~ __ i=i Fig. 4.—Section along the£Dore and Totley Tunnel. LINACRE BORINO • STUBBING EDGE COLLIERY apperknowle BORING (^Pe/on Silk stone Coal 390 ft from turfact) Fig. 3.—Sections illustrating the Lower Coal Measures. picturesque type of scenery follows naturally from the greater abundance and strength of sandy deposits in these lower coal measures. From an economic point of view the most, important change is the failure of the Kilburn coal, for it is present as a workable seam only in the extreme south, near South Wingfields These lower coal measures contain none of the principal seams of the coalfield, though the. Mickley Thin coal in their upper part is a good seam, and the Alton of some local importance. The coals fall into two main groups, an earlier comprising the Alton coal with four or five other thin seams in the lower part, and a later group consisting of the Mickley coals and four or five associated seams near the top of the sequence. Besides these, one or two thin coals occur in the middle of the measures, within or just above the Wingfield flagstones, at or near the horizon of the Kilburn coal. Apart from the apparent absence of the last-named, the grouping of the coals is the same as in the southern part of this coalfield and in those of North Staffordshire.* The general persistence of these groups of coal seams suggests the persistence of individual coals, but except in the case of the Alton this can rarely be proved for any great distance. Associated with the coals of the upper and lower groups, but more particularly with those of the lower, * See “ Southern Part of the Derbyshire, etc., Coalfield,” Mem. Geol. Surv., 1908, p. 72. are several beds of, gannister and fireclay, more numerous and in greater demand for economic use than is the case further south. Between these two groups of coal seams the Wing- field flagstones, usually underlain by some 200 ft. of shale, comprise the Brincliffe Edge rock or Eiland flags of Yorkshire, and form another connecting link between the northern and southern parts of the coalfield, while by no means confined to the eastern half of the North Midland coalfields. The part of the lower coal measures that shows the greatest variation of thickness and character is that below the Alton coal. On the whole this part exhibits, on both sides of the Pennine saddle, a striking northerly increase of thickness between extreme limits of less than 60 ft. and about 300 ft. But immediately west- ward of Baslow these beds remain comparatively thin much further north than might be expected on the hypothesis of a uniform northerly thickening. We may note, however, the somewhat greater proximity of these comparatively thin measures to the greatest elevation of the Pennine axis as shown in the limestones. Middle Coal Measures.—As previously stated, this division of the coal measures contains the chief beds of coal, of which the approximate positions in the sequence are given in the following table :— Ft. Measures with thin seams.................. 800 + Clowne coal.......................... 3 to 4 Measures with thin seams............... 260 to 400 High Hazles coal .................... 3 to 4 Measures with thin seams............... 300 to 400 Top Hard coal........................ 5 to 7 Measures with Waterloo and Ell coals... 600 Deep Soft coal....................... 3 to 5 Measures, chiefly sandstone in the north ... 50 to 140 Deep Hard coal .................. .... 3 to 6 Measures with Piper (Hospital) coals .... 200 Tupton (furnace) or Low Main Coal.... 3 to 6 Measures with Yard coal ................. 200 Silkstone coal....................... 4 to 6 Below the Top Hard the positions and number of the coals, as illustrated by shaft sections, show only slight variations; while above the Top Hard the seams, excepting the High Hazles, are fitful in their occur- rence. Among the chief workable seams the Silkstone, Deep Hard and Top Hard take precedence on account of their superior quality and persistence. The Silkstone coal and the Deep Hard are also well-known Yorkshire seams, the latter under the name of the Parkgate coal; while the Top Hard or Barnsley coal of Yorkshire is equally famous, and, with an average thickness, ranging from 4 ft. to 5 ft. of high of high-class marketable coal, is now known to extend several miles eastward under the permian and triassic rocks. Originally it also certainly stretched to the west beyond its present out- crop; but, excluding this factor, and including only what remains in the visible and what lies in the con- cealed coalfield, this valuable seam has an extension of at least 900 square miles. In the present area sandstones sometimes rest directly on, but more generally occur a few feet above the main seams, in which case the intervening strata consist of shales or sandy shales with nodules of iron- stone. Each seam usually has its seat-earth consisting of unstratified clay with or without rootlets. Shales bulk largely, but except those above the Clowne coal, in which the Mansfield marine bed, 740 ft. above the Top Hard, occurs, they are not especially developed on any definite horizon like that of the great body of shale below the Wingfield flagstones in the lower coal measures. Neither, apart from the Mansfield marine bed, does any bed afford characters peculiar to itself, though the shales below the Top Hard coal are perhaps usually less arenaceous, and contain more nodules of ironstone, grouped in layers, than occur in those above this seam. Structure.—The most important structures are those of the Brimington and Norton-Ridgeway anticlines with the supplementary synclines of Sheepbridge and Dron- field. On the flanks of the anticlines the chief coals rise up somewhat steeply, and are brought rapidly to the surface; but owing to the sudden decrease in dip a short distance from the anticlines they lie at much shallower depths in the deeper part of the main synclinal fold of the coalfield than would be expected from the dips observed in the proximity of the anticlines. At Temple Normanton a sag down in the Brimington anticline introduces a basin containing the Top Hard coal, but south of Stainsby the anticlinal uplift again asserts itself, though it does not bring to the surface measures lower than the Deep Hard coal. In the Sheepbridge and Dronfield synclines the highest measures involved in the fold are those associ- ated with the Deep Soft and Deep Hard coal. The faults traversing the middle coal measures are neither numerous nor of large throws. Between Teversal and Calow the anticlinal disturbance is diagonally crossed by a faulted belt, which can be resolved into a major fracture on the west with a down- throw west, of 150 ft. in the Silkstone coal west of Hardstoft; and a second fracture on the east, with a downthrow east, of 309 ft. in the Silkstone coal beneath Suttonspring Wood. As the faults cross the anticline the throws decrease, but they increase on entering the Sheepbridge syncline at Chesterfield, where a fault with