2. Notes on the Granite Surfaces of Mount Sorrel. By Professor W. W. WATTS, F.R.S. It has been suggested that some of the grooved and polished surfaces known in this circle and in certain other Midland localities may be due to wind action in Pleistocene times. A recently discovered section at Mount Sorrel showed glacial striæ trending N. 10° W. on a set of wind-grooves trending about E. and W. Proof is thus given that the Triassic wind-grooves have survived actual glaciation, and may thus be expected to have been able to resist other less drastic methods of recent and Pleistocene denudation. 3. The Ordovician Sequence in the Cader Idris District (Merioneth). By ARTHUR HUBERT COX, M.Sc., Ph.D., F.G.S., and ALFRED KINGSLEY WELLS. Reference was made to the work of previous observers, including Sedgwick, Ramsay, Cole and Jennings, Geikie, and Lake and Reynolds. The Cader Idris range is formed by a great escarpment of Ordovician igneous rocks, facing northwards across Barmouth Estuary towards the Harlech dome. The igneous rocks were for long regarded as being all of Arenig age. Re-examination of the area has shown the presence of four distinct volcanic series among the Ordovician rocks, and the following descending sequence has been established:: Glenkiln-Hartfell (X.) Talyllyn Mud- Grey-blue banded mudstones with Amplexograptus arctus in the lowest beds . 800 ft. stones (I.) Basement Beds. Striped arenaceous flags and grits 100 ft. Upper Cambrian Unconformity Tremadoc Beds Both acid and basic rocks occur as sills at numerous horizons. The basic rocks are diabases of various types, all with the felspars considerably albitised and usually with primary quartz. The acid rocks are soda-granophyres. The granophyre intrusions cut and are later than the basic intrusions, and locally hybrid rocks appear to have been formed along the junctions. No basic intrusions have been found above the Upper Basic Volcanic Series, and no acid intrusions above the Upper Acid Series, and it is noteworthy that the granophyres appear to be closely related to the extrusive rhyolites among which they are intruded. This fixes an upper limit to the age of the diabases in this district. The various beds strike more or less east to west, and dip steadily southwards at about 40° until the Talyllyn Mudstones are reached, when folding and rolling of the beds immediately begin. Two N.E.-S.W. shatter faults-the Dolgelley and Talyllyn faults-cause a certain amount of repetition, and give rise to the DolgelleyLlyn Gwernon and to the Talyllyn Valleys, the former to the north and the latter to the south of the escarpment. A strike-fault between Mynydd Gader and Cader Idris cuts out the whole of the Bifidus Beds, bringing the Lower Acid and the Lower Basic Volcanic Series against one another. The intrusive rocks frequently cause local variations in the dip and strike. All the softer strata are strongly cleaved, so that fossils are difficult to obtain, The slates within the Lower Acid Series have yielded a few extensiform graptolites, while from the Bifidus Beds the characteristic fossils were obtained at numerous localities. The D. murchisoni zone has not been recognised by the authors, its place presumably being occupied by a part of the Lower Basic Series. The dark mudstones among which the pisolitic iron-ore is developed have yielded rather obscure graptolites, which, however, indicate a fairly high horizon in the Llandeilo Series. The presence of Amplexograptus arctus and Glyptograptus teretiusculus var. euglyphus in the lowest beds of the Talyllyn Mudstones indicates a high horizon in the Glenkiln, or, in other words, a low horizon in the Caradocian, and suggests that the immediately underlying Upper Acid Series is at approximately the same horizon as the Snowdonian volcanic rocks of Conway. This youngest of the four volcanic series on Cader Idris is therefore considerably higher in the Ordovician than has been previously supposed. The position of the boundary between Caradocian and Llandeilian has not yet been established, owing to the unfossiliferous character of the blue-grey mudstones of Llyn-y-Gader and Llyn Cau. One of the authors (A. H. Cox) is indebted to the Government Grant Committee of the Royal Society for a grant which has partially defrayed the expenses involved in the investigation. The area is being mapped on the 6-inch scale. 4. On the Underground Contours of the Barnsley Seam of Coal in the Yorkshire Coalfield. By Professor W. G. FEARNSIDES, M.A. In this paper the author presents a preliminary account of the results of his statistical analysis of about a hundred records of borings and sinkings which have proved the depth of the Barnsley Bed or its equivalents (the Gawthorpe, the Warren House Coals of Yorkshire, and the Top Hard Coal of Derbyshire) in Yorkshire. The majority of the records of borings and sinkings discussed have been collected by a committee of the Midland Institute of Mining, Civil and Mechanical Engineers,' published by that Institution in volume form in 1914, the sites at which the information was obtained being plotted on a halfinch map. The depths to the coal have been corrected for the height of the surface location above sea-level, and, after the manner of Dr. Gibson's map (Plate 1) in the Geological Survey Memoir on the Concealed Coalfield,' contour lines have been drawn among the spot levels so obtained. Other contour lines similarly obtained from the records of borings which have passed through Permian strata show the character of the surface of the Coal Measures where they underlie the Permian strata. In drawing the contour lines no attempt has been made to distinguish between those changes of level in the seam between neighbouring pits which are due to faulting and those due to the folding of the strata. Since, however, over most of the coalfield the faults tend to nullify the change of level which the dip has accomplished, it is maintained by the author that to plot contours which show the average rate of change of level is a statistical process which can be demonstrated as approximating to truth. (1) From an analysis of the results as plotted it appears that the underground contours in the Barnsley Bed (strike lines) in Yorkshire in detail generally range either N.E.-S. W. or N.W.-S. E., and that within the area under which the Barnsley Bed has actually been proved by working it is difficult to find either a N.-S. or an E.-W. strike constant over more than a few miles of country. This circumstance, if general over the coalfield, would seem to demand some revision of current views respecting the origin and structure of the Pennine Chain.1 (2) The greatest structural division of the coalfield 'basin' is by the equivalent of a N.E.-S.W. anticline of which the southern limb is along the line of the Don faults from Sheffield by Rotherham and Conisborough to Doncaster. North of this line there is some evidence for the existence of a syncline with its axis central near Frickley. In ground from which the Permian rocks have been denuded, the coal attains a depth exceeding 1,800 feet below sea-level. The general line of this northern trough follows a N.W.S.E. trend from Wakefield to South Kirkby, whence, displaced perhaps by the Don anticline, it bends somewhat eastward through Bulcroft. South of the Don a wider trough, also trending N.W.-S. E. through Yorkshire Main Colliery (Edlington and Bawtry), carries the Barnsley bed (at Rossington) below 2,600 feet. (3) The inclination of the Barnsley Bed is at its steepest near the outcrop, and, after the manner of gentle folds, the measures flatten out when the centre line of the syncline is approached. There is no evidence to suggest any general eastward rise of the Barnsley Seam within the area plotted on the map. (The eastern boundary of the map is through Thorne and Retford.) (4) By the plotting of the contour lines on Bartholomew's layer-coloured halfinch contour map the interdependence of underground structure and topographical relief in the area of the exposed coalfield has been well brought out. Over the whole coalfield most of the ridges are of escarpment form and elongate along the line of strike; but from the map it becomes evident that, wherever the strike of the Barnsley Bed shows a change of direction, there the escarpment ridges are found upstanding above their average height, and this whether they form the arches or lie in the troughs of the folds. From his experience of the application of the contour method to the study of the tectonics of the Barnsley Bed, the author suggests that the method is of peculiar usefulness in coalfield work. He offers this preliminary account of the results of his work in Yorkshire in the hope that workers on the western side of the Pennines may take up the method and use it in the further investiga tion of the many and difficult problems of geological structure presented by the Back-bone of England.' 5. Sixth Report on Excavations among the Cambrian Rocks of Comley, Shropshire. By E. S. COBBOLD.-See Reports, p. 117. FRIDAY, SEPTEMBER 10. The following Papers and Reports were read :— 1. On the Restoration of certain Fossils by Serial Sections. Examples of fossils reconstructed from serial sections were exhibited. They include a graptolite, Prionograptus; a primitive fish, Palæospondylus; the skull of a reptile from the Karoo, Dicynodon; and the skull of another reptile, These views were admirably expressed by Prof. E. Hull, who in advocating them in 1868 succinctly remarked (Q.J.G.S. 1869, p. 331): Immediately upon the close of the Carboniferous period the northern limits of the York shire and Lancashire coalfields were determined by the upheaval and denudation of the beds along east and west lines, while the coalfields themselves remained in their original continuity across the region now formed of the Pennine hills from Skipton southwards, and that at the close of the Permian period these coalfields were dissevered by the uprising of the area now formed of the Pennine Range by lines of upheaval ranging from north to south.' Ichthyosaurus communis, from the Lower Lias of Lyme Regis. The lastnamed, 520 mm. in length, had been studied in 520 sections taken at equal intervals apart, which revealed in remarkable detail the internal structure with a completeness hitherto unknown. 2. Vertebrate Life Zones in the Permo-Trias. By D. M. S. WATSON. 3. The Corrosive Action of certain Brines in Manitoba. Brine springs issue from Middle and Upper Devonian limestones and dolomites at the foot of the Manitoban escarpment. At least eighty brine areas are known, with a total flow during the dry season-of approximately 500 gallons per minute. The water circulates in the Dakota Sandstone, the basal member of the Cretaceous series, and extends laterally into the Devonian calciferous formations, from which it leaches sodium chloride, disseminated through certain dolomite horizons. The composition of the brines, expressed in percentages of total solids, is very similar to that of sea-water. It is a somewhat purer solution of sodium chloride, and also a more concentrated solution, than seawater, the percentage salinity being 5-7 (sea-water 3:5). The salt-flats where the springs reach the surface are devoid of vegetation, and studded with ice-carried boulders. These are representative of the preCambrian igneous series of North-Central Canada-granites, gneisses, and epidiorites. They have suffered intense chemical disintegration, large boulders having been reduced to half their original size. Different minerals have been affected to different extents, but not even quartz or garnet has escaped corrosion. Ferromagnesians have been most intensely affected; and gneissose structures, hardly noticeable on unweathered surfaces, stand clearly revealed. The striking difference between the action of these brines and that of seawater calls for explanation. Thin crusts of salt gather, during the summer months, on the flats and around the boulders. The salt is somewhat deliquescent; and thin films of brine are drawn, by surface tension, over the surface of the boulders. Water in contact with the atmosphere is a powerful disintegrant. Alkalies are removed as chlorides or carbonates, and silica and alumina are precipitated as gels, separately or in combination. The gels exercise selective adsorption on the salts of the brine, alkali being taken up and the brine being left richer in the acid radicals. The brine is thereby rendered a more active disintegrating agent, and the process goes on continuously. The function of the dissolved salts is considered to be twofold: (1) they provide a thin film of liquid in contact with atmospheric oxygen; (2) owing to partial adsorption by colloids, they provide an acid residual solution, which is a powerful corrosive agent. The evidences of the corrosive action of sea-water on beach boulders are, no doubt, obscured by mechanical attrition due to wave action. Such corrosion cannot, however, be compared in intensity with that of the brines. Boulders between high- and low-water mark are alternately submerged and dry to the base a state of affairs inimical to the persistence of thin films of liquid on the surface of the boulders. The initial conditions are consequently wanting; and the relative immunity of beach boulders from chemical corrosion is due, not to any inability of sea-water to act as a corrosive, but to the absence of favourable conditions for the activity of the solution. 4. The Carboniferous Limestone Zones of N.E. Lancashire. The sequence is well seen in the neighbourhood of Clitheroe, where numerous quarries have been opened up. The lowest beds exposed are near Chatburn mill, and are dark, thinly-bedded limestones with calcareous shale partings. Fossils are very scarce. There is a great thickness of these almost unfossiliferous beds, the top parts of which are dolomitic. Bold Venture Quarry, Horrocksford Quarry, and several other exposures snow beds in probably Lower C. with numerous small Zaphrentids (chiefly Zaphrentis Omaliusi, with the variety ambigua of Mr. R. G. Carruthers very common). Higher parts of these beds contain Canina cylindrica, which has been found at Brungerly Bridge, in Bold Venture Quarry, at Pimlico, and at Downham. This species is not so common or well-developed as in beds farther east, towards Hellifield and district. Among the brachiopods are Chonetes comoides, Orthotetes crenistria, &c. Large gasteropods such as Euomphalus pentangulatus and Bellerophon cornuarietis are common. Conocardium hibernicum is a characteristic lamellibranch. Above these beds come the lowest beds with Productus sub-lævis, and the Knoll beds of Coplaw, lower part of Worsaw, &c. Here are the typical C. knolls with numerous brachiopods, the gasteropods mentioned above, but few corals. Amplexus coralloides is, however, common and Michelinia sp. Above these are well-bedded crinoidal limestones, leading up to the probably C.-S. knolls of Salt Hill, Bellman Park, Worsaw, &c. These beds contain a rich brachiopod fauna, quite distinct, however, from that of Elbolton. Whilst Productus pustulosus, Pr. semireticularis, Spirifer striatus, &c., are quite common, one never finds Pr. striatus, Pr. martini and other D. forms so common in those eastern knolls. A fairly rich coral fauna has lately been discovered in these C.-S. or S. knolls; it has not yet been worked out, however. There is probably an unconformity at this level, and then there succeeds a great thickness of shales with limestones, with few fossils. These would appear to be on the same horizon as the richly fossiliferous beds of Elbolton. Above these shales with limestones come the Pendleside limestones, black limestones with cherts, and with irregular bands of more fossiliferous limestone. The Ravensholme limestone appears to be similar and to contain some of the same fauna as the highest limestone at Cracoe and the limestone of the railway quarry at Rylstone described by the writer. The Sabden shales succeed these beds, and lead up to the Millstone Grit series. A map was exhibited on which some of these generalisations were shown. 5. A Brief Criticism of the Fauna of the Limestone Beds at Treak Cliff and Peakshill, Castleton, Derbyshire. By HENRY DAY, M.Sc. The author put forward some observations on a collection of some three hundred species of Carboniferous Limestone fossils from the localities Treak Cliff and Peakshill, Castleton, and embracing about one hundred species of brachiopods and corals. The beds at both places may be referred to the brachiopod beds' of Sibly (Q.J.G.S. 1908'), and what are allocated by him to sub-zone D,— the Lonsdalia sub-zone. The present list of species presents some features of considerable interest bearing on the value of certain types as zonal indices. Reference is made to Vaughan's paper on the Bristol area, where it is indicated that amongst the brachiopod groups confined to the Tournaisian in that area are the following: Productus cf. Martini; Leptena analoga; Schizophoria resupinata; Rhipidomella aff. Michelini; Spiriferina octoplicata; Syringothyris cuspidata. Two of these, it is noted, Spiriferina octoplicata and Schizophoria resupinata, are sub-zonal indices, and each with its maximum in its sub-zone. The list of Castleton forms from well up in D, now presented, includes all the above-mentioned brachiopod groups. Syringothyris cuspidata and Spiriferina octoplicata are fairly abundant at both Treak Cliff and Peakshill, Schizophoria resupinata is extremely abundant at both places, Leptena analoga is abundant, whilst Productus cf. Martini and Rhipidomella Michelini are rare. Passing to the coral fauna, the genus Zaphrentis appears in the Castleton list, i.e., one of the two genera of corals confined to the Tournaisian in the Bristol area and not extending into the Viséan. The genus, though not very abundant, is represented by several species. In addition, the genera Michelinia and Amplexus, characteristic of the Upper Tournaisian of Bristol, but possibly extending into the base of the Viséan, are cited in the Castleton list, Michelinia |
