714 1HE COLLIERY GUARDIAN. April 4, 1913. THE GEOLOGY ANO PALEONTOLOGY OF THE WARWICKSHIRE COALFIELD * By Robert Douglas Vernon, B.A., B.Sc., F.G.S. (Continued from page 641.) Palaeontology. With the exception of a few plants in the museum of the Warwickshire Naturalists’ Field-Club at Warwick, there appears to be no public collection of fossils from the coalfield. This branch of the subject had thus remained a virgin field for research, and in the following account I am concerned solely with the fossils which I have myself collected during the past three years. It is, however, necessary to add that, since this work was completed, a list of fossils from the coal measures of Warwickshire has been published.f These fossils, which were collected and identified by Mr. A. R. Horwood, are restricted to middle coal-measure forms of plants and freshwater lamelhbranchs, from the subdivisions of the Thick coal worked in the collieries of the neighbourhood of Nuneaton. Each of the four subdivisions of the coal measures— the productive measures, the Nuneaton clays, the Haunchwood sandstones and the Keele beds—has yielded fossil plants, and from the productive measures an extensive fauna has been collected. Fossils have also been obtained from the permian deposits. The whole of the flora and fauna considered has been obtained from artificial sections, such as clay pits, colliery tip heaps and the cores from deep borings for coal. The nomenclature of the seams of coal is still somewhat confused, and so it is extremely probable that, in some cases, the same seam has received distinct names at different collieries. As might, perhaps, have been expected, the various subdivisions of the Thick coal— including the Four-feet, Two-yard, Ryder, Bare, Eiland slate coals—were found to constitute one palaeontological horizon, from which the greater part of the Middle coal measure flora, together with most of the freshwater lamellibranchiata, has been obtained. Most of the collieries work one or more of the divisions of the Thick coal, together with one or more of the lower seams; and, as the resulting debris of shale is thrown on the waste heaps, it naturally becomes mixed, so that it has not always been possible to refer each fossil to its exact horizon. In most cases it is a question of distinguishing the debris of the Thick coal from that of the Seven-feet coal; and, as the latter yields only a marine fauna, the problem of correlating fossils with the seams from which they come is considerably simplified. The localities and stratigraphical horizons of each of the fossiliferous sections are stated in the following table:— For convenience of reference, the chief palaeontological horizons may be summarised as follows :— Permian Kenilworth sandstone... Plant-bed. Keele beds..................... Haunchwood sandstones ..... Plant-bed. Three limestones with Spirorbis and ostracoda. Plant-bed. Limestones with Spirorbis and ostracoda. r Plant bed. \ Limestone with ] fishes, Spirorbis C and ostracoda. Plant-bed. r Plant-bed. < Mussel-band. C Fish-bed. ( Marine bed. ( Fish-bed. ( Plant-bed. ( Fish-bed. Nuneaton clays ................ Upper beds of Middle coal measures, Four-Feet coal"| Two-Yard coal | Ryder coal J- Thick coal Ell coal | Slate coal J Seven-feet coal......:............ Double coal Bench coal ) The flora of the productive measures of Warwick- shire is a typical Middle coal-measure flora. It is dis- tinguished from the flora of the transition series and the upper coal measures by the fact that many of the species have never been recorded from these higher horizons. The majority of the species occur both in the Middle coal measures and in the Lower coal measures of Britain; but the presence of a number of plants, such as Oligocarpia brongniarti, Zeilleria delicatula, and Lonchopteris bricei, which are restricted to the Middle coal measures of Britain, at once differentiates the flora from that of the Lower coal measures. It may perhaps be contended that a thin representa- tive of the Lower coal measures might be present in the north of the Warwickshire coalfield, where the thickness of productive coal measures reaches its maximum. From the presence of Lepidophloios laricinus and Calamocladus charseformis, which are unknown from * Abstract of a p*per read before the Geological Society of London and published in the Quarterly Journal of the society. t Rep. Brit. Assoc. (Portsmouth) 1911, p. 105. Synopsis of the Carboniferous and Permian Formations of Warwickshire. Name. Characters. Chief fossils. Thickness. Permian. Calcareous, false-bedded red sand- stones and lenticular red marls spotted with green ; with two horizons of limestone conglomerates, the lowest of which forms the base. Walchia sp. Walchia imbricata (Schimper). . Calamites sp. Dasyceps bucklandi (Lloyd). Oxyodon britannicus (von Huene). Feet. ? 1,000 Keele beds. Haunch wood sandstones. Nuneaton clays. Middle coal measures. i I Red and purple sandstones and marls, with marly breccias and, towards the base, beds of grey sand- stone. Three thin beds of Spirorbis limestone, the lowest (and thickest) of which is taken as the base. Grey sandstones and shales, with thin coals and Spirorbis limestones; some red mottled marls towards the top. Red and purple mottled marls and • clays, with thin Espley rocks, a i Spirorbis limestone, and local - breccias. Grey sandstones, shales, and under- clays, with thick coalseams and beds of ironstone. Sandstones and breccias towards the top, which thicken north-, wards. An impersistent conglomerate forms the base. 1 Walchia sp. Pecopterispolymorpha (Brongn.). Pecopteris arborescens (Schlotheim). Pecopteris miltoni (Artis). Spirorbis. Ostracoda. Annularia stellata (Schlotheim). Neuropteris ovata (Hoffmann). Neuropteris scheuchzeri (Hoffmann). Neuropteris rarinervis (Bunb). Pecopteris miltoni (Artis). Sphenophy llumemarginatum (Brongn.). i eaia leidyi var. salteriana (J nes). Cordaites principalis (Gerinar). Calamites sp. Spii orbis. Ostracoda Fish-remains undetermined. Neuropteris schlehani (Stur). Zeilleria, delicatula (Sternb.). Sijillaria elongata (Brongn.). Lingub i mytiloides (Sow.). Myalina compressa (Hind). Pterinopecten papyraceus (Sow.). Carbonicola aquilina (Sow.). Anthracomya williamsoni (Brown). Naiadites cannata (Sow.). Megalichthys hibberti (Agassiz). Rhizodopsis sauroides (Willm.). Acanthodes wardi (Egerton). 1,000 to 1,500 300 to 450 80 to 150 400 in the south to 700 in the north the Lower coal measures of Britain, it is concluded that in the Warwickshire coalfield the Lower coal measures are entirely absent, and that the lowest palaeobotanical horizon is that of the Middle coal measures. On field evidence the arenacious strata containing a few thin coals, which occur between the Thick coal and the Nuneaton clays, have been included in the Middle coal measures; while the Nuneaton clays and the Haunchwood sandstones, the latter being also an arenaceous series with one or more thin coals, have been placed with the Keele beds in the Upper coal measures. The absence of typical Upper coal-measure species and the abundance of Neuropteris gigantea are sufficient evidence to prove that the beds immediately above the Thick coal, including the Four-Feet sand- stone, are Middle coal measures. We may now conclude that the whole of the lower or productive division of the coal measures of Warwick- shire, up to the base of the Nuneaton clays, is of Middle coal-measure age. The upper or barren coal measures are next con- sidered. In the list of the fossil plants which have been obtained from the Keele beds, the Haunchwood sand- stones, and the Nuneaton clays, if we exclude the variety of Pecopteris miltoni and the ubiquitous Stig- maria ficoides, there remain twelve species. Two of these range throughout, and two occur in the three uppermost divisions ; while four species are restricted to the Upper coal measures and transition series, and two are only known to occur in the Upper coal measures. It is clear, therefore, that this is an Upper coal measure flora. The abundance of Pecopteris polymorpha in the Keele beds is evidence of their Upper coal measure age. In the Haunch wood sandstones we have a mixture of forms. The Upper coal measure species P. polymorpha, which is very rare at this horizon, occurs, together with an abundance of such typical Transition species as Neuropteris scheuchzeri, N. ovata, N. rarinervis and Sphenophyllum emarginatum. The Haunchwood sand- stones must, therefore, be referred to the Transition series, in which the red Nuneaton clays may also be placed. The striking contrast between the rich flora of the Middle coal measures and the meagre flora of the Transition series and the Upper coal measures, raises an important question with regard to the meaning of this difference. The partial extinction of the Middle coal measures species of plants, and the incoming of the Upper coal measure pecopterids and conifers (which are essentially Stephanian species ranging upwards into the permian), appears to have taken place during the period of formation of the Nuneaton clays. At the same time the abundant fauna of the Middle coal measures becomes reduced to a few species of fishes, ostracoda and Spirorbis. We may expect such profound palaeontological changes to have been accompanied by important changes in the lithological characters of the deposits then in course of formation, and, in fact, such is the case. The Nuneaton clays mark the appearance of the first red sediments among the grey rocks of the coal measures. In these red strata are found the first Espley rocks and Spirobis limestones, while rocks foreign to the coalfield now become common as pebbles in the breccias. These breccias in the Nuneaton clays suggest that a local unconformity may occur at this horizon, an opinion which receives some support from the fact that there is in Warwickshire no equivalent of the black- band group of North Staffordshire. In conclusion, it may be affirmed that the horizon of the Nuneaton clays marks the initiation of those Continental conditions in the English Midlands, which continued throughout permian and triassic times. In addition to the fossil flora recorded above, the Middle coal measures have also yielded evidence of an extensive fauna. The collection includes fishes, Crustacea and mollusca. It is noteworthy that in a list of fresh water lamellibranchiata there is a complete absence of those forms, such as Carbonicola robusta, which in other coalfields are restricted to the Lower coal measures. And, further, all the species recorded are common Middle coal-measure fossils. This suggests that the productive coal measures must be of Middle coal- measure age—a conclusion which agrees with that arrived at from a study of the fossil flora. The bulk of the coal-measure sediments of this coal- field were undoubtedly laid down in fresh water, and the abundant remains of a terrestrial flora which they contain indicate the proximity of land throughout the time that elapsed during the deposition of the beds. But, during one period, the subsidence was of such an extent that, the sea invaded the area, and the deposits thus formed contain marine forms of animal life. This marine bed occurs in the roof of the Seven-feet coal; it consists of dark blue shale, containing hard ovoid nodules of clay ironstone. Fossils are found both in the shale and in the ironstone ; but in the former they are usually crushed flat, while in the latter uncrushed specimens may sometimes be found. The marine shale, which contains a large amount of pyrite disseminated through it, has a characteristic mode of weathering quite different from that of ordinary non-marine coal- measure shales; and this is accompanied by the formation of selenite, which usually occurs as radiating masses of crystals. The ironstones are but little affected by exposure to the atmosphere, and thus it has been possible to collect fossiliferous nodules from the waste- tips of collieries which have been abandoned for at least 30 years. The marine bed appears to be invariably present immediately above the Seven-Feet coal, through- out the whole of the northern portion of the coalfield.* Apparently the cephalopoda are entirely absent, and the lamellibranchiata predominate over the brachiopoda. Three of the species in this bed are exceedingly common; they are:—Lingula mytiloides (Sow.), Pterinopecten papyraceus (Sow.), and Myalina compressa (Hind). The first two are also abundant in the marine beds of other coalfields; but M. compressa, which is the characteristic fossil of this bed, is not common in other areas. At least three fish-bearing beds have been detected in the Middle coal measures, and their position in the sequence is shown below:— 1. Thick coal (and its constituent seams: the Ryder coal and the Slate coal). 2. Seven-Feet coal. (Fish-band in the marine bed.) o (" Double and ’ ( Bench coals. * Another marine bed may be present above the Thick coal; but on this point palaeontological evidence is still incomplete.