The following Papers and Report were read: 1. Some Points of Special Interest in the Geology of the Neighbourhood of Oxford. By Professor A. H. GREEN, M.A., F.R.S. There are several spots around Oxford the names of which have come to be household words in the literature of geology. It is not likely that I can add anything to what has been long known about localities which were favourite haunts of Buckland, Phillips, and other of our foremost geologists. But, as excursions to some of these places have been planned, I hoped it might be serviceable to recall attention to the more important of the specialities of these spots. We hope to visit historic Stonesfield. Work will be begun at some brick-and ironstone-pits at Fawler, where the Liassic zones of Ammonites capricornus, A. margaritatus, and A. spinatus are well shown. Above these comes an attenuated representative of the Upper Lias, not more than 10 feet thick. The basement bed, with its mixture of ammonites elsewhere relegated to separate zones, which has been studied by Mr. Walford, is present. Above the Upper Lias we have the representative of the Inferior Oolite, here reduced to the two bands of Chipping Norton Limestone. Clypeus Grit. The latter is referred to the Parkinsoni zone, the lower zones of the subformation being here absent. On the hill above lie the workings in the Stonesfield Slate, with its mixture of terrestrial, fresh water, and marine forms, too well known to need special description. Quarries may afterwards be visited in Great Oolite (Upper Zone), Forest Marble, and Cornbrash, one of which shows a curious case of contemporaneous erosion. An excursion over Shotover will show a succession from the Oxford Clay to the Neocomian Ironsands. One point of interest here is the little coral reefs of the Corallian Beds, and the bank of finely comminuted material, derived from their wear, which adjoins them. The Portland Beds are sandy and shingly, and mark the margin of the southern Portlandian sea. 2 The Neocomian Ironsands are part of a long strip which runs from Wiltshire, through Oxfordshire and Bedfordshire, to Cambridgeshire and onwards. They are coarse, shingly, very current-bedded, obviously shore deposits. Possibly they were formed in a long strait that connected the northern and southern Neocomian basins. At most of the spots where they yield fossils, these are marine. But it is only natural that, as we go along a coast line where the physical conditions change from place to place, there should be a corresponding change in the character and fossils of the deposits. And it is so here. On a hill adjoining Shotover the Ironsands have long been known to contain fresh-water fossils. We are here facing what was the mouth of a river. At Faringdon, again, the beds depart widely from their normal type. There is no current bedding, indeed very little bedding at all. Their abundant fossils include sponges, most of which are very perfect, and delicate bryozoa but little worn, with scattered specimens of perfect brachiopods, all embedded in a matrix of very finely comminuted organisms. These facts seem to me to point to a tract of still water such as would be found in a sheltered bay. In the deeper water of the centre the fossils would be preserved entire, while over the shallow margins they would be ground small, and the finely comminuted matter swept into the central pit till it was filled up. An interesting section occurs in a brick-pit near Culham. It shows 3. Gault clay, with a band at the bottom containing sand, pebbles, and rolled fossils derived from the Neocomian Ironsands. 2. Thin band of earthy limestone; Kimmeridgian (?) or Portlandian. 1. Kimmeridge Clay. Walford, Q.J.G.S., xli. (1885), p. 38. 2 Blake and Hudleston, Q.J.G.S., xxxiii. (1877), pp. 308–311. The Neocomian Ironsands are in full force hard by; at this spot they have been denuded before the Gault was deposited, and their ruins have accumulated towards the base of that subformation. The Purbeck and Portland rocks of the Swindon outlier have been so often described that they need no special notice. The shell-marks and tufaceous limestones of the Purbeck lie in a hollow worn out in the Portland rocks, and the two are most sharply marked off from each other. A limestone crowded with Cerithium Portlandicum marks the upper limit of the Portland. It has been irregularly denuded, and here and there small isolated blocks, which have escaped denudation, project up into the Purbeck. The Portlands have a shingly character in some beds, which must have been formed in shallow water. 2. Report of the Committee for making new Sections in the Stonesfield Slate.-See Reports, p. 304. 3. On the Terraced Hill Slopes of North Oxfordshire. The green slopes of many of the minor vales of North Oxfordshire are scored with parallel terraces or terraced banks, frequently of such regularity in depth of step and slope as to present to the mind any other origin for their formation than that of the every-day work of natural forces. They have been described as camps, entrenchments, and amphitheatres, and those of other districts Mr. Gomme has described, and has cited the many theories of their origin. Mr. Walford first drew attention to the Oxfordshire and Warwickshire terraced fields in 1886,2 and dealt at greater length with the subject in 1890.3 He gives as causes of formation- 1. The downward creep of the surface and sub-surface soil. 2. The occurrence of the terraces upon one precise geologic line, the micaceous marls of the Middle Lias which come in below the Red Rock bed. The marls are porous and non-cohesive. On the slippery slopes the soil must creep. The rain and rain-wash loosen the light soil below and about the roots of the herbage and urge its movement downward. Terraces from an incipient stage, like an ordinary grass ridge, to minor and major terraced banks of varying regularity of form can be traced. Below these marls are depths of compact blue clay (the zone of Ammonites margaritatus if in near contact with the marls). A little below the point where the marls and clays meet is the line of water outflow. Along the line there is constant removal of marl by chemical and mechanical solution. The effect is the loosening and sliding of the land downwards and outwards. This movement is aided by the weight of the overlying mass of rock, sometimes twenty-five feet in thickness. 3. Free passage of water through the rock and marl is necessary, for the Upper Lias clays have, on the Oxfordshire terraced hills, either been wholly stripped from the hill top or pushed back by atmospheric denudation. Regularly terraced slopes are not found on clay-covered hills; the appearance of terraces is coincident with the wearing away of the clay 'roof.' The amphitheatre form of terraced land is always a valley head. The outflow of the stream-the valley-maker-marks ordinarily the base of the amphitheatre. More frequently the terraces of the valley head are small in step and their curvature is broken. Such an instance is Kenhill, near Shennington. An instance of greater regularity of curvature and greater depth of step is the Beargarden, Banbury. Blake, Q.J.G.S., xxxvi. (1880), p. 203. 2 E. A. Walford, Edge Hill: the Battle and Battlefield, p. 24. Banbury, 1886. E. A. Walford, 'On some Terraced Hill Slopes in the Midlands,' Journ. Northampton Nat. Hist. Soc., January, 1890. From the Edge Hill escarpment a fork of the Horton vale runs alongside Adsum Plantation, and makes what is known as Adsum Hollow. The terraces sweep in regular curves along the high banks of the stream, and where it joins the main vale to the North of Horley the steps are so prominent as to give the name of Steps Meadow to the ground. Gredenton Hill, on the Burton Darrett range, is very regularly and beautifully terraced on three sides. The author does not attempt description of the chalk hills or the lynchets of Dorsetshire. The sandy marls of the Dorsetshire Inferior Oolite have a composition approaching that of the micaceous marls of the Midlands, and reasons like those brought forward will no doubt prove their similar mode of formation. The Probable Range of the Coal-Measures under the Newer Rocks of Oxfordshire and the Adjoining Counties. By Professor BOYD DAWKINS, F.R.S. The principle laid down by Godwin-Austen and Prestwich that the master or tectonic folds in the pre-Carboniferous and Carboniferous rocks are lines of weakness along which the newer rocks have been folded in later times, has been recently applied by Bertrand to the district of northern France. In the present communication the author proposes to see how far it can be used in the search after the buried coal-fields of the counties of Oxford, Buckingham, Berks, and Wilts. From the relation existing between the tectonic anticlines and synclines in the districts of South Wales, Gloucester, and the West of England, where they can be studied at the surface in the Palæozoic rocks, most important conclusions may be drawn as to the coal-fields buried under the newer rocks in southern England. They are as follows: 1. The Mid-Devon syncline, traceable eastwards until it cuts the sea-line near Bognor. 2. The North Devon anticline, which runs eastwards through the Vale of Wardour, past Salisbury, and along the anticline of the Weald from Petersfield to Dungeness. 3. The Mid-Somerset syncline, which sweeps eastwards through the Vale of Bridgewater and Glastonbury, through the chalk downs between Heytesbury and Hindon, to Haslemere. From this point it is continued to the east through Tunbridge Wells and Tenterden to the sea to the south of Hythe. These three folds have no bearing on the range of the coal-fields in the drainage area of the Thames. The fourth, or Pembroke-Mendip anticline, and the fifth, or South Welsh syncline, are the two great tectonic folds which remain for consideration. The Pembroke-Mendip anticlinal range, highly faulted and folded, is traceable westwards into South Ireland, and eastwards, through Pembroke and the peninsula of Gower, to the south of Cardiff, through Weston-super-Mare and the Mendip Hills. Throughout this area it forms the southern margin of the coal-fields. Near Frome it plunges beneath the Oolites. It is, however, clearly marked by the Upper Greensand anticline of the Vale of Pewsey, and by the Upper Greensand inliers of Ham and Kingsclere. Thence it passes along the line to the high downs past Basingstoke and Farnham to Peasemarsh, south of Guildford, where it is seen in an inlier of Weald clay. It is carried still further to the east by similar inliers south of Westerham, and at Wateringbury and Maidstone. From Maidstone it sweeps to the south-east, through Otham and Ashford, arriving at the coast close to Hythe. In the eastern portion of its course it has, in my opinion, been the chief factor causing the south-eastern trend of the North Downs in the district of Maidstone. It forms also the southern boundary of the South-eastern coal-field discovered in the boring at Dover, and of the coal-fields of northern France and Belgium. The South Welsh syncline, only two miles wide at St. Bride's Bay, in the anthracite district of Pembroke, widens out into the coal-field of South Wales, twenty miles in width. As it approaches the upper estuary of the Severn it is represented by the outlying coal-field of the Forest of Dean, and the three partially or wholly covered fields to the north of the Mendip Hills, distributed through an area measuring forty-five miles from north to south. The wedge-like syncline, with its more or less connected coal-fields, continues to widen eastwards, its northern boundary being probably represented by a line drawn from the northern rim of the South Welsh coal-field to the north of the Forest of Dean, and continued due east beneath the Secondary and Tertiary rocks to some point between Walton-onthe-Naze and the mouth of the Blackwater. It passes through Gloucester, Rissington, in the valley of the Windrush, Blenheim, Kirtlington, Quainton, Luton, Bishop's Stortford, Dunmow, Braintree, and Colchester. The width of this great tectonic syncline between Colchester and Dover is about fifty miles, and it occupies nearly the whole of the London Tertiary basin, which, it must be noted, is of the same wedge shape, widening to the east. The boring recently described by Mr. Whitaker at Culford, near Bury St. Edmunds, in which a slate rock, probably of Silurian or pre-Silurian age, was struck at a depth of 637 feet 6 inches from the surface, shows that in all probability that area is an anticlinal area. About forty-two miles to the south, in the deep boring at Harwich, the Yoredale shales come in. Both these points are, be it remarked, to the north of the line in question. Both indicate a Palæozoic area in Suffolk and northern Essex older than the Coal-Measures, and similar to that on the same meridian in South Wales and Gloucestershire which lies to the north of the western coal-fields. We have, therefore, not merely a well-defined PembrokeMendip anticline forming the southern boundary of the coal-fields both in the west and in the east, as proved by the south-eastern coal-field at Dover, but also evidence of the continuation of the South Welsh pre-Carboniferous barrier of Hull, which forms the northern boundary of the visible coal-fields due eastwards into Suffolk. It may therefore be reasonably inferred that similar coal-fields, isolated from each other by tracts of older rocks, are to be found in the South Welsh syncline where it lies buried beneath the Secondary and Tertiary strata. In other words, we may conclude that there are coal-fields in North Wilts, in the counties of Berks, Oxford, and Buckingham, and the Tertiary basin of the Thames within the limits laid down above, and in a direction indicated in 1871 by the Coal Commissioners. One such coal-field, indeed, has already been discovered in a deep boring at Burford, near Whitney, in the valley of the Windrush. The discovery, however, has unfortunately not been followed up, and we do not know whether it is of wide east and west range, similar to that of South Wales, or of Bethune and Namur, or whether it is small and unimportant, like some of the smaller coal-basins north of the Mendip Hills. It offers a sure basis for other deep borings, which may have the same industrial effect on Oxfordshire as those which have extended the range of the buried Coal-Measures in northern France, ninety miles to the west of Charleroi, and converted a purely agricultural into a great manufacturing district. There is no practical difficulty arising from the depth at which the Coal-Measures may be expected to occur in this region. At Burford they were struck at 1,184 feet from the surface, and at Dover at 1,113 feet below high-water mark. The borings in the area of the London Tertiaries prove that the Palæozoic rocks are not buried to a greater depth than about 1,200 feet below sea-level, and in Hertfordshire to as little as 796 feet. The most important collieries in England are carried on at depths ranging from 1,500 to more than 3,000 feet. The new light thrown upon the question of the buried coal-fields by recent discoveries places it in a very different position from that which it occupied in 1871, when Godwin-Austen, Prestwich, and Hull gave their evidence before the Royal Commission. The boring at Dover, revealing the existence of a valuable coal-field, now offers a fixed point for further discovery in south-eastern England. That at Burford offers a similar basis for the proving of the Oxfordshire coal-field. The many other wells and borings made in the area of London, and as far north as Bury St. Edmunds, also afford important information as to the northern boundary of the productive South Welsh syncline. The development of our mineral wealth is of such vast importance that it would be quite worth the while of the Government to undertake a series of experimental borings, which would indicate the exact position of the buried coal-fields. In the present state of the mining laws it is a task not likely to be undertaken by the private adventurer. It might, however, be carried out by the County Councils, or by a combination of landowners, either with or without a compulsory rate, on the property which would be benefited by the discovery of new fields. It is one of those objects of public utility which are especially worthy of the regard of the British Association at this time and in this place. 5. On the Deposit of Iron Ore in the Boring at Shakespeare Cliff, Dover. By Professor BOYD DAWKINS, F.R.S. The general results of the boring at Dover were laid before the British Association at Cardiff in 1892, so far as relates to the discovery of the south-eastern coalfield. In the present communication the author treats of a bed of ironstone, which is likely to be of great importance in the new industries which will spring up sooner or later in Kent in consequence of the discovery of coal in workable quantities. The strata penetrated in the boring are as follows: Feet Coal-measures with twelve seams of coal 23 feet 5 inches thick The ironstone occurs in the Kimmeridgian part of the section, and as shown in the following details : :- Grey nodular limestone Flaggy sandstone Grey sandy clay Dark bituminous shale Coralline Oolite with the usual fossils, Pecten vagans, &c. The ironstone presents very singular physical characters. It is composed of small dark-brown shining grains of hydrated oxide of iron like millet seed, embedded 7 27 2 27 |