Wenlock Rocks Research Articles

Isotope-geochemical characteristics of Wenlock carbonate and terrigenous-carbonate deposits of the Subpolar Urals and the southern part of the Chernyshev ridge

Research subject. Wenlock deposits in the Subpolar Urals and southern part of the Chernyshev Ridge. Materials and methods. Carbonate and terrigenous-carbonate rock samples from sections of the Subpolar Urals (outcrops 212, 217) and the southern part of the Chernyshev Ridge (outcrop 479) were studied by isotope analysis of carbonate carbon and oxygen.Results. The isotopic composition of the studied sections varies across a wide range of δ13С (–6.4…–0.05‰) and δ18O (20.0–26.9‰). Therefore, three time intervals characterized by distinctive isotopic characteristics can be distinguished, roughly corresponding to early Sheinwoodian (I), late Sheinwoodian (II) and Homerian (III). Interval I is characterized exclusively by the rocks of outcrop 479 with δ13С (–3.6…–3.0‰) and δ18O (22.4–23.6‰). In Interval II, the average values of isotopic characteristics of outcrop 479 indicate a tendency to weighting carbon (–5.5…–3.5‰) and somewhat heavier oxygen (23.2–25.2‰) isotopes. In outcrop 212, the average isotopic values for carbon and oxygen vary from –2.9 to –1.3‰ and from 21.9 to 24.3‰, respectively. In outcrop 217, the average values are δ13C (–1.8…–0.8‰) and δ18O (22.4–25.4‰). In Interval III, the average values of carbon isotopic composition in outcrop 479 are becoming heavier from –2.5 to –0.7‰. In outcrop 212, the isotopic values of oxygen (21.9–23.1‰) and carbon (–4.9…–2.5‰) tend to become weighting; however, in outcrop 217, the average isotopic values of δ13C (–1.9…–0.5‰) and δ18O (22.3–24.5‰) remain constant. The conducted litho-facial studies showed that the weighting carbon isotopic composition ranging from –6.4…to –3.0‰ is associated with an increase in microbial activity in sediments, the manifestation of vadose-phreatic conditions, and the intake of light carbon dioxide with a flow of terrigenous material from the earth. In the latter case, oxygen isotopic values are also the most lightweight (20.0–23.0‰).Conclusions. The obtained isotopic characteristics of the Wenlock rocks under study indicate the expedience of identifying three time intervals and their correlation with paleogeographic reconstructions of Wenlockian sedimentation in the Timan-northern Ural region.

The early Silurian pentamerid brachiopodCostistricklandia canadensis(Billings, 1859) and its biostratigraphic and paleobiogeographic significance

Costistricklandiais a common, easily recognizable pentamerid brachiopod in upper Llandovery to lowest Wenlock rocks of eastern Laurentia, Avalonia and Baltica. In this paper, the poorly knownCostistricklandia canadensis(Billings) is re-described from the upper Telychian Rockway Dolomite of the Niagara Escarpment, Ontario. Compared to the relatively complete record of theStricklandia-Costistricklandiaevolution in the Welsh Borderland and the Baltic region, true representatives of theStricklandia lenslineage are sporadic in North America, including those from the Merrimack Formation of Anticosti Island, the Red Mountain Formation of Alabama, the Hopkinton Formation of Iowa, and the Nonda Formation of the northern Rocky Mountains. Although the exact mode of speciation in theStricklandia-Costistricklandiaand thePentamerus-Pentameroidestransitions remains debatable, the common association ofCostistricklandiaandPentameroidesmake them a useful concurrent biozone for correlating middle to upper Telychian rocks of North America and Europe. Paleobiogeographically, thePentameroides-CostistricklandiaFauna marks the third major pulse of pentamerid faunal migration between Laurentia and its adjacent paleo-plates during the Early Silurian, following the limited intercontinental dispersal of the early LlandoveryVirgianaFauna and the quasi-cosmopolitan dispersal of the middle LlandoveryPentamerusFauna.

THE EARLY SILURIAN PENTAMERID BRACHIOPOD COSTISTRICKLANDIA CANADENSIS (BILLINGS, 1859) AND ITS BIOSTRATIGRAPHIC AND PALEOBIOGEOGRAPHIC SIGNIFICANCE

Costistricklandia is a common, easily recognizable pentamerid brachiopod in upper Llandovery to lowest Wenlock rocks of eastern Laurentia, Avalonia and Baltica. In this paper, the poorly known Costistricklandia canadensis (Billings) is re-described from the upper Telychian Rockway Dolomite of the Niagara Escarpment, Ontario. Compared to the relatively complete record of the Stricklandia-Costistricklandia evolution in the Welsh Borderland and the Baltic region, true representatives of the Stricklandia lens lineage are sporadic in North America, including those from the Merrimack Formation of Anticosti Island, the Red Mountain Formation of Alabama, the Hopkinton Formation of Iowa, and the Nonda Formation of the northern Rocky Mountains. Although the exact mode of speciation in the Stricklandia-Costistricklandia and the Pentamerus-Pentameroides transitions remains debatable, the common association of Costistricklandia and Pentameroides make them a useful concurrent biozone for correlating middle to upper Telychian rocks of North America and Europe. Paleobiogeographically, the Pentameroides-Costistricklandia Fauna marks the third major pulse of pentamerid faunal migration between Laurentia and its adjacent paleo-plates during the Early Silurian, following the limited intercontinental dispersal of the early Llandovery Virgiana Fauna and the quasi-cosmopolitan dispersal of the middle Llandovery Pentamerus Fauna.

An Early Ordovician age for the Annascaul Formation of the SE Dingle Peninsula, SW Ireland

The phyllitic mudrocks, quartz wacke sandstones and mélange units of the Annascaul Formation in the SE Dingle Peninsula, SW Ireland have been previously assumed to be Silurian in age, similar to overlying fossiliferous Wenlock rocks of the Ballynane Member. The contact between the Ballynane Member and the underlying Annascaul beds is either faulted or unconformable , and the Annascaul mudrocks contain two or more cleavages not present in the Silurian Ballynane and younger strata. The Ballynane Member is therefore differentiated from the Annascaul Formation by upgrading the proven Wenlock Ballynane beds to formational status. Grey and black mudrocks in the Annascaul Formation have yielded diagnostic palynomorph assemblages indicative of an Early Ordovician age. The Annascaul Formation invites comparison with similar Early Ordovician rocks, south of the putative trace of the Iapetus Suture, in SE and eastern Ireland, in the English Lake District, and in central Newfoundland.

Geological structure and tectonic evolution of the Lower Palaeozoic rocks of the Isle of Man

Abstract The Lower Palaeozoic sedimentary rocks of the Isle of Man, deposited near the margin of the Avalonian plate, were folded and cleaved during continental closure and collision. Although folds on a scale of several kilometres can be inferred, the large-scale structure of the Isle of Man remains uncertain in the absence of detailed and widespread biostratigraphical controls on the stratigraphy and other difficulties. A working model suggests that the island is composed of several northeast trending, strike-parallel ‘tracts’ separated by vertical or steeply northwest dipping faults. Stratigraphic sequences may be apparent within tracts but cannot easily be correlated between tracts. The within-tract structure is the result of two main stages of deformation (D1 and D2) and one or more localized later events (D3). F1 folds have axial surfaces which dip steeply northwest or southeast, near-horizontal hinges, and wavelengths ranging up to several kilometres. The F2 folds, seen mostly on a small scale, are reclined to recumbent and coaxial with F1 folds. The D1 and D2 structures were imposed on the Wenlock rocks of the Niarbyl Formation but are absent from the Peel Sandstone (late Silurian-early Devonian), constraining the main deformation to the Caledonian (Acadian) orogeny. The D1 structures are the products of collisional tectonics but the origin of the flat-lying D2 structures is unclear, although vertical flattening is more likely than thrusting. Most of the inferred tract-bounding structures cannot be characterized in the absence of exposure or precise stratigraphical controls. Two of them, however, are inferred to be northwest dipping faults. One of these faults cuts D1 structures whilst the other appears to be pinned by a syn-D1 intrusion, suggesting broadly syn-D1 age. Localized, steep northeast striking zones of late to post-D1 high strain, which are exposed on the west coast of the island, in part reflect partitioning of coaxial or transpressive deformation into the boundaries between rocks of contrasted ductility. The Niarbyl Fault Zone (‘shear zone’) is shown to be a belt of ductile and brittle deformation whose tectonic history and regional significance have yet to be fully resolved. Brittle thrust faults are exposed in several parts of the Isle of Man and include the Niarbyl Thrust, which, in one interpretation, is taken to separate the Niarbyl high-strain phyllonite belt from the overlying Niarbyl Formation. Most thrusts are north to northwest dipping and displacements are typically on a metre scale. Many of them may be attributed to the latest stages of the Caledonian collision processes on the basis that similar structures also deform the late Silurian-early Devonian Peel Sandstone of the Isle of Man and rocks of similar age elsewhere in the region.

Discussion

Dr H. C. S quirrell welcomed the detailed account of the thelodonts, a group long-neglected by British geologists despite their value in both local and worldwide correlation. He asked the author if the sudden appearance of Turinia pagei could be of use in establishing the Downtonian-Dittonian junction in the Welsh Borders, the precise position of which has yet to be agreed. The speaker questioned the statement that the fauna of the Ludlow Bone Bed is essentially no different from the earlier Silurian assemblages. Fig. 6 shows that ten species of thelodonts have been obtained from the Ludlow Bone Bed, but only five of these are found in the Ludlow and Wenlock rocks below. There appears to be a significant difference between the faunas found below and above the base of the bone bed. He also questioned the validity of moving the Silurian-Devonian boundary up to the base of the ‘ Psammosteus’ Limestone Group solely on the evidence of the thelodont faunas. As there is a faunal change at the base of the Ludlow Bone Bed, it would seem more logical to retain the boundary there, thus keeping the mainly fish-bearing rocks of the Down-tonian within the Devonian. The Author replied: The position of the incoming of the Turinia assemblage agrees well with the boundary chosen by the Geological Survey to denote the Downton-Ditton boundary in the Brown Glee region (Greig et al. 1968). This, as most boundaries in this succession, including the Ludlow bone bed, is a facies boundary. The fauna of

The stratigraphy and structure of the Silurian (Wenlock) rocks south-east of Hawick, Roxburghshire, Scotland

Re-mapping for the first time since 1899 has led to a re-interpretation of the succession and structure previously advocated for the Hawick area (Peach & Home 1899). Palaeontological and lithological evidence and ‘way-up’ criteria provide the basis for a completely revised stratigraphy proposed for the Wenlock rocks. Two facies are present, those of the Hawick and Riccarton Groups, each of which constitutes over 12 000 ft of strata. Four new stratigraphical divisions are erected in the Riccarton Group: the Stobs Castle, Shankend, Penchrise Burn, and Caddroun Burn Beds; and the Wenlock graptolite zones of Cyrtograptus murchisoni, Monograptus riccartonensis, C. symmetricus, and C. lundgreni are recognized. The graptolite faunas bear close similarities to the Wenlock assemblages of Bohemia, a feature most noticeable among the cyrtograptids, where the dominant basal Wenlock forms are C. insectus and C. centrifugus. Structurally, the area comprises five main units, each of which consists of one or more north-facing asymmetrical folds of Caledonoid trend. The units are separated by major high-angle faults, which are mainly reverse faults. Minor faults, especially wrench-faults, are important.

The petrography, sedimentation and provenance of the Wenlock rocks near Hawick, Roxburghshire

A petrographical description of the sediments is given, with particular reference to stratigraphical variation and provenance. It is concluded that the material was derived from a land-mass consisting largely of Ordovician spilites, cherts, acid lavas and sediments; together with metamorphic rocks, probably Dalradian, arkoses and granitic intrusions. The provenance conclusions are supported by the directional current structures, which indicate a predominantly north-westerly derivation for these rocks. The lithology of the greywackes and interbedded sediments is consistent with their deposition by turbidity currents, about which some new details are deduced. Furthermore, the evidence of current directions and variations in lithology suggest that the two Wenlock facies represent deposition on a “submarine-delta” (Hawick Group) and in fan accumulations in deeper water, at the mouths of submarine canyons (Riccarton Group). The area of Wenlock deposition is believed to have been separated by the Ordovician/Dalradian land-mass from a contemporaneous trough at Lesmahagow; but to have been in communication with the area of deposition in the Lake District.

Discussion

The P resident asked whether the author had considered the possibility that, in some cases illustrated, the epifauna had settled on the shell after the death of the brachiopod; he referred in particular to the lantern-slide showing epifauna on the brachiopod interarea. Professor T. N eville G eorge referred to the occurrence of similar epifaunal associations on shells of both Silurian and Carboniferous age in rocks of comparable facies. Eospirifer from the Wenlock Limestone not uncommonly was a base for attachment of both polyzoans and auloporoid corals, and “ Spirifer ” in Tournaisian and Viséan shales of a variety of sessile forms including Cladochonus and serpulids. There was, however, no obviously preferred shell-type as host; and other brachiopods, including pentameraceans and orthaceans in Wenlock rocks, and productaceans and orthotetaceans in Carboniferous, were as often the convenient base as spirifers —and molluscs in the Lias as often as Spiriferina. There was little doubt that the “selection” of a base by an attached form was completely accidental: in life-history the change from a planktonic to a benthic habit by the growing individual was a passive fall onto a randomly variable sea-floor, with survival dependent on the chance of attachment to whatever hard base scattered shells might provide. The concentration of epifaunal growth on the stouter dorsal valve of the spirifers was also a feature of Silurian and Carboniferous forms, and, combined with the usually clear umbones and interarea, suggested the life-posture of the spirifers to be as the author inferred. The delthyrial structures of those few spirifers

The geology of the Silurian rocks west and south of the Carneddau Range, Radnorshire

Summary An account is given of the geological succession from the Upper Llandovery to the lower part of the Lower Ludlow. The former group is developed in two distinct facies—an eastern facies of calcareous sandstones with Pentamerus oblongus , and a western facies of green mudstones and dark shales containing Monograptus crenulatus and other graptolites. The Wenlock rocks are dark graptolitic shales which have been divided into two sub-groups. They include the six graptolite zones erected by Dr. G. L. Elles in 1900. The Lower Ludlow rocks consist of shales with Monograptus nilssoni . In the Upper Wenlock and above the M. nilssoni shales there are important developments of slumped mudstones which have been mapped in detail. The area is a shallow syncline traversed by a series of powerful faults ranging mainly in the direction of the strike. Some of them behave as block faults. One fault appears to be a tear which has shifted earlier faults. Cleavage is sporadically developed.

Societies and Academies

LONDON. Geological Society, June 26. R. 0. Roberts: The geology of the district around Abbey-Cwmhir (Radnorshire). This paper deals with an area of about 30 square miles in north-western Radnorshire. The rocks belong to the Bala, Valentian, and Wenlock Series. Only the lowest beds of the Birkhill Stage are exposed, and they are overstepped by the Tarannon Stage, which, over most of the area, rests directly on folded Bala rocks. The Bala rocks are exposed along the north-eastern extension of the Towy antieline; but, in this district, the anticlinal axis is partly replaced by an import- ant strike-fault, which hades westwards. Subsidiary folds may be recognised within the Bala rocks. The axes of these folds are parallel to the general strike of the strata, although there is a change in the direction of pitch around Nantmel. The Bala rocks were folded in pre-Tarannon times, but broad shallow folds in the Tarannon and Wenlock rocks indicate that there has been a repetition of folding along the same lines at different periods. C. A. Matley and A. Heard:

Societies and Academies

LONDON. Geological Society, March n.—O. T. Jones: The geology of the Llandovery district (Carmarthenshire). The district lies east of the town of Llandovery, and extends for about 10 miles from north-east to southwest. It is divisible into a northern area and a southern area, each area the succession is fairly complete, but in between them it is greatly attenuated. In proceeding from south to north, certain lithological changes have been noted in the Lower Llandovery. The fauna in the rocks appears in the main to have been drifted into the area from an adjoining tract, lying probably nearer to the shore-line. In addition to the differential subsidence and uplift along lines trending north-east and south-west, there is evidence of repeated elevation and depression along nearly east-and-west axes. The axes of these transverse movements appear to have persisted during the whole of the Llandovery epoch, but there is no evidence of them in the Wenlock rocks.--G. Andrew: (i) The Llandovery and associated rocks of Garth (Brecon-shire). The Llandovery rocks lie north-west of Garth railway station, and extend from there in the direction of Newbridge. The Lower Llandovery rocks overlie the Bala with a sharp boundary, but with apparent conformity. The Middle Llandovery occurs in one small outcrop in the centre of the area, and is rapidly overstepped by the Upper"Llandovery in both directions. The Upper Llandovery consists of two types, a lower comprising sandy mudstones with Pentamerus oblongus, etc., and an upper of pale mudstones ("Tarannon Pale Shales "). (2) The relations between the Llandovery rocks of Llandovery and those of Garth. At Garth, as at Llandovery, the Lower and Middle Llandovery rocks are overstepped both north and south by Upper Llandovery or Wenlock deposits. At Garth they crop out Jin an elongated oval area; at Llandovery they form two roughly oval areas. The Middle Llandovery and the higher divisions of the Lower Llandovery are represented only in the central regions. These distributions are due to the fact that differential movements along nearly east-and-west axes (that is, transversely to the present strike) were in progress during the Llandovery epoch. The regions where the older Llandovery rocks are most complete were regions of persistent subsidence. The axes of elevation in both areas cross the present strike at practically regular intervals of about 5 miles, and the areas of subsidence are situated nearly midway between them. Linnean Society, March 19.—S. Hirst: Species of mites of the family Trombidiidae found on lizards. When more than one form occurs on the same host, a flattened form lives under the scales, and a rounded form between the toes or toe pads. In view of the considerable differences in the shape of the setae, etc., these are regarded at present as distinct species.-o Mrs. Muriel Roach: A study of the physiology of certain soil alga; in pure culture. Although a very few species carried on the synthesis of organic substance from carbon-dioxide and water through the agency of sunlight, the great majority of those studied grew much better when supplied with an additional source of carbon, glucose being especially favourable to many species. A single species was selected for a more detailed investigation of the effect of different organic substances on its growth in liquid media. The alga was able to grow in complete darkness, given a suitable supply of food, at about half the rate that it grew in the same medium in the light. The logarithmic values of the bulk for the first nine or ten days, in media completely favourable to the growth of the organism, lie on a straight line. The data indicate the importance of the compound interest law which evidently underlies the growth of the organism during the initial part of its growth. The theory of the auto-catalytic nature of growth does not appear to hold.-J. M. Brown: Some Collembola from Mesopotamia. Fifteen species of Collembola collected mainly in the neighbourhood of Bagdad and Amara, in Mesopotamia. Ten species and one variety are regarded as new. The Collembolan fauna of Mesopotamia shows much closer affinity with that of the Palasarctic than with that of either the Oriental or the Ethiopian regions.

The Geological Structure of Central Wales and the Adjoining Regions

I. Introduction. The region herein discussed is that portion of Wales which lies, roughly, between the River Dovey and Pembrokeshire; it is bounded on the west by the coast of Cardigan Bay, and on the east by an irregular line coinciding in part with the base of the Wenlock rocks and in part with the margin of the Upper Palæozoic rocks. It comprises, therefore, the whole of Cardiganshire and a great part of Carmarthenshire and Pembrokeshire, together with portions of Montgomeryshire, Breconshire, and Radnorshire—an area exceeding 1800 square miles in extent. This tract is represented upon geological maps by ‘Lower Silurian’ colour, only diversified by small areas indicating igneous rocks, or by tracts of yellow dots indicating grits and sandstones. Ever since the days when Sedgwick and Murchison laboured to introduce order among the old slaty and volcanic rocks of Wales the region defined above has always remained something of a geological puzzle: the apparent uniformity and unfossiliferous character of the strata over wide areas, and the compression which they have suffered by folding, faulting, and cleavage, combined to defy for a long time all attempts at unravelling its structure. In more recent years the discovery of numerous fossiliferous beds among these strata has made possible the application of the zonal method, based in this case upon the range in time of various genera and species of graptolites. By this method, combined with close attention to the lithological characters of the rocks, attacks have been made upon this ‘geological wilderness,’

Excursions for Seasons 1906 and 1907

To New Collieries at Olive Bank and New Craighall, Niddrie, Midlothian, on Saturday, 24th March—Mr. Robert Martin, manager, conductor—a joint excursion with Edinburgh Geological Society. For a description of these Collieries see a paper by Mr. Martin in the recently published part (vol. viii., part 3) of the Transactions of the Edinburgh Geological Society. To South Queensferry, Linlithgowshire, on Saturday, 7th April—Mr. H. M. Cadell of Grange, B.Sc., conductor—a joint excursion with Edinburgh Geological Society. Oil shales and the Burdiehouse Limestone, with intrusive igneous rocks. To Aberfoyle, Perthshire, on Saturday, 7th April—Mr. Peter Macnair, hon. secretary, conductor. The party entered the Loch Katrine Aqueduct where it cuts through the boundary fault, and proceeding northwards passed successively through the jasper beds, the black shales and cherts, and the grits. They then returned and examined the rocks on the south side of the fault; these include limestones, conglomerates of Old Red Sandstone age, and a bed of vesicular andesite interbedded with the conglomerates. To Lesmahagow, Lanarkshire, on Monday, 16th April (Spring Holiday)—Mr, Peter Macnair, hon. secretary, conductor. In the Upper Silurian inlier of Lesmahagow, the rocks are folded into a dome-shaped anticline, with the Wenlock rocks in the centre. These pass upwards into the Ludlow, Downtonian, and Old Red Sandstone formations. The party went by the Birkenhead Burn and returned by the Logan Water. An opportunity was thus given of examining the general structure of the inlier, and of visiting the principal fossiliferous horizons. To Kilmacolm, Renfrewshire, on Saturday, 21st April—Mr. Alex. This 250-word extract was created in the absence of an abstract

I.—On the Occurrence of the Genus Turrilepas, H. Woodw., and Annelid Jaws in the Upper Silurian (? Wenlock) Rocks of New South Wales

The correspondence in the life of the Wenlock rocks of Great Britain and those probably occupying a similar horizon in New South Wales is a very marked one. At present, I wish more particularly to draw attention to the occurrence of the genus Turrilepas and Annelid jaws in the Bowning Beds of New South Wales. This series of rocks has been enthusiastically investigated by Mr. John Mitchell, who, in his capacity of Teacher of the Public School of that place for some years, had an excellent opportunity of working out the fauna of the series in question. His researches are detailed in two papers, “Notes on the Geology of Bowning,” and “The Geological Sequence of the Bowning Beds.” Both the plates of Turrilepas and the small Annelid jaws are found in the Lower Trilobite bed of this series, and are chiefly from the typical locality of Bowning Creek.

Notes on the Palæontology of the Wenlock Shales of Shropshire

In his presidential address to the Geological Society, Feb., 1881, Mr. Robert Etheridge gave a full synopsis of the then known British Wenlock fauna. The number of genera and species that had been tabulated up to that time were, for 13 groups of fossils, 171 genera and 536 species. He also stated that 58 genera and 125 species were “common to the Wenlock rocks aud the Upper Llandovery: or in other words these 125 species pass up from the Llandovery to the Wenlock formation.”* The geographical distribution of these species include North and South Wales, Westmoreland, Scotland, and Ireland. By far the greater number enumerated are found in the Wenlock limestone series, the debris of which has been so persistently searched for fossils, both by the palaeontological student and by the general dealer in fossil organisms, and the results of their united investigations are by no means surprising. In the Catalogue of Fossils in the School of Mines (1878) the whole of the Cambrian and Silurian fauna are carefully tabulated, stratagraphically, and while the Wenlock limestone fauna occupies twenty-three pages of the catalogue, the fauna of the Wenlock shales, to which attention will be presently directed, are catalogued on ten pages only. In the same presidential address Mr. Etheridge furnished a series of tables of the distribution of species in the different Palaeozoic horizons, which to the student of Stratagraphical Palaeontology is most valuable. The whole of the then known Wenlock shale fauna were included in twelve classes, and are ...

On Annelid Jaws from the Wenlock and Ludlow Formations of the West of England

I n the paper which I had the honour to bring before the Society in the early part of last year, on Annelid jaws from the Palæozoic rocks of Canada and Scotland*, I ventured to express an opinion that these small bodies would be very likely found in rocks of similar age in this country. Since that time I have had the opportunity of searching various exposures of the Silurian rocks at Dudley, Much Wenlock, and Iron Bridge, in Shropshire, all well-known localities for Wenlock fossils ; and in each place I have discovered Annelid jaws more or less abundantly. In quarries at Stoke-Edith, and near Ludlow, the rocks of Upper Ludlow age also yielded these remains, though by no means so abundantly or in such a good state of preservation as the Wenlock rocks—a result perhaps rather owing to the less favourable character of the matrix for their preservation and to the more limited exposures of the rock-surfaces than to any deficiency in the number of the Annelids. Altogether, from the above-mentioned localities my search produced between two and three hundred specimens of these minute remains : but the greater number of these proved on examination to be only fragmentary specimens ; many perish in the process of cleaning them away from the matrix ; and thus only about one fourth of the total number are available for description. It is a matter of surprise that these fossils, occurring thus numerously in a district renowned as a classical hunting-ground for

On the Mode of Occurrence and Derivation of Beds of Drifted Coal near Corwen, North Wales

A bout four years ago the late Mr. Jones, of Angharad, directed my attention to the remarkable fact that beds of drifted coal are to be found in sand and gravel around Corwen, at a great distance from any known coal in situ . The belief that this coal was of local derivation had led to unsuccessful mining operations in the Wenlock rocks of the neighbourhood. Positions occupied by the Drifted Coal. -Around Corwen the lowest drift consist of yellowish (occasionally bluish) clay, irregularly alternating with beds of coarse gravel. Many large boulders are to near its summit. The former are often rounded and local; the latter subungular, or angular, and erratic (chiefly from the Arenig hills to the west). Above this drift there is a deposit of clean sand and fine gravel, which, in other parts of the Dee valley, often graduates into very coarse gravel with boulders. In many places around Corwen this deposit is covered by an irregular kind of brick clay. The coal is generally found in the sand and fine gravel. Immediately to the east of the mountain-limestone quarry (about a mile and a half to the west of Corwen), a roadside section shows fine gravel and sand with streaks of decomposed coal. In the Dee valley, some distance east of Corwen, and not far from Carrog station, consideraqble quantities of coal may be found in many other places around Corwen; but the principal instance occurs to the north of the town, and near to where the Denbigh

Note on the graptolites found by Mr Henderson at Habbie’s Howe, Logan Burn

The graptolites obtained by Mr Henderson from the shaly Silurian beds of Habbie’s Howe, and which I have had in my possession for determination, belong at least to three distinct genera. The most frequent fossil (marked 1 on the pieces of shale exhibited) is a peculiar form, which is usually held to be merely a variety of Monograptus colonus (Barrande). It differs from the typical form in several minor respects, such as the shape of the thecae, the direction of the apertural spines, the rate of taper in the polypary, c in the Wenlock rocks of South Roxburghshire, and in the Wenlock and Lower Ludlow of the typical Siluria. The variety under notice has been

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,