THE QUARTERLY JOURNAL OF THE GEOLOGICAL SOCIETY OF LONDON. PROCEEDINGS OF THE GEOLOGICAL SOCIETY. POSTPONED PAPERS. 1. On ABNORMAL CONDITIONS of SECONDARY DEPOSITS when connected with the SOMERSETSHIRE and SOUTH WALES COAL-BASIN; and on the age of the SUTTON and SOUTHERNDOWN SERIES. BY CHARLES MOORE, Esq., F.G.S. I. Introduction. 1. Old Red Sandstone. (Read March 20, 1867.*) c. Insect and Crustacean Beds. 3. Rhætic and Liassic Beds within a. Section of Keuper, Rhætic, Lower, Middle, and Upper Lias, and Oolite at Camerton. b. Section in Munger Road Quarry. 4. Relative thickness of Secondary Beds South and North of the Mendips. 5. Whatley Lias and Fontaineétoupe-Four. 6. Mells Middle Lias and Coal. For the other communications read at this Evening-meeting see p. 197. VOL. XXIII.-PART I, 2 I 8. Value of Zones of Zoological Life. VI. The South Wales District. 1. Penarth Rhætic and Liassic Section. 2. Bridgend Liassic Sections. 3. Cowbridge Section. 4. Llanbethian Quarries. 5. Laleston Quarry. 6. Stormy Quarry. 7. Section at Ewenney. a. Local Deposition of the Sut- b. Organic remains from the Sutton Stone. c. The Ammonites-Bucklandi Beds. 10. Langan Lead-mine.. 11. Inadmissibility of the term "Infralias." VII. Conclusion. VIII. Description of Organic re mains. IX. List of Fossils, I. INTRODUCTION. My attention has for some time been directed to the peculiar physical conditions under which many of the Secondary rocks have been deposited on the southern edge and in the interior of the Somersetshire Coal-basin, and to the remarkable evidences of unconformability everywhere present. My observations have also been extended into South Wales, where to a considerable extent the same phenomena prevail. Within the last two years I have on several occasions accompanied friends to the interesting coast-sections of Sutton and Southerndown, which have lately been the subject of a paper by Mr. Tawney, when I have pointed out that, instead of representing, as they are supposed by him to do, beds older than the Rhætic and probably on the horizon of the St. Cassian or Muschelkalk deposits, they are only abnormal conditions of the Liassic rocks which are so familiar to us in many parts of England and on the continent. Elaborate physical descriptions of some parts of the districts I shall have to notice have already been given by Messrs. Buckland and Conybeare, in the Geological Transactions*, under the title of Observations on the South-western Coal-district of England," and more recently by the late Sir Henry De la Beche, in a paper contained in the Memoirs of the Geological Survey, "On the Formation of the Rocks of South Wales and the South-west of England.” I shall hereafter have to refer to some interesting points not discussed in these Memoirs. * 2nd series, vol. i. part 2. II. THE MENDIP HILLS. This range of hills, which gives so marked a physical character, and has helped so much to modify the geology of the county of Somerset, commences near Frome, and passes, almost uninterruptedly, thence to Weston-super-Mare on the Bristol Channel. The connexion of the Mendip Hills with rocks of the same age on the southern flanks of the South Wales Coal-basin may be traced by the exposures of Carboniferous Limestone in the islands of the Steep and Flat Holmes of the Bristol Channel, and of these again with small exposures of the same beds on the opposite coast. The continuity of the Mendip Hills with the latter is therefore pretty clearly indicated; and it is not improbable that their elevation may have been contemporaneous and due to the same physical cause. Although on the South Wales coast Secondary rocks prevail, there is probably but little doubt that they only lie unconformably upon the Carboniferous Limestone and the Old Red Sandstone not far beneath. Measuring in a direct line from Oldford in a north-westerly direction to Weston-super-Mare, the length of the Mendips may be estimated at about thirty-five miles. 1. Old Red Sandstone.-Just north of the town of Frome, the Old Red Sandstone may be seen emerging from beneath the Inferior Oolite in a narrow strip nearly a mile in length, at Spring Garden, and having on its southern slope a thin band of Carboniferous Limestone. The Old Red Sandstone is next seen at Little Elm, whence it continues in the Mendips for some miles, and is the oldest stratified formation in this chain of hills. It has its largest development north-east of the town of Shepton Mallet, and again at North Hill and Blackdown; and in the Bristol district it is found on the Leigh and Weston Down. 2. The Carboniferous Limestone.-A mile west of the Carboniferous Limestone previously mentioned, this formation appears in several pretty combes, one leading from Frome by way of the Vallis to Elm and Mells, in the Murder Combe, and in a narrow wooded defile known as the Whatley Combe, in which are situated the ruins of Nunney Castle. Towards the southern end of this are the quarries of Holwell, the fissures in which have yielded so large a series of Rhætic organic remains. Resting upon the Old Red Sandstone, which usually forms the more elevated portion of the Mendip range, the Carboniferous Limestone is seen to continue almost uninterruptedly to the Bristol Channel, and thence along the southern portion of the South Wales Coal-field. 3. Basaltic Dyke.-There is abundant evidence throughout the whole of this district that the upheaval and disturbance of the beds forming the Mendip Hills were caused by volcanic action; but indications at the surface of the presence of intrusive rocks had never been observed, probably owing to the gradual rise of their northern slope, their well-cultivated surface, and the general encroachment of Secondary deposits along their flanks, Hitherto the Old Red Sandstone has been considered the central axis of the Mendips; but I have now the satisfaction of announcing that during last summer (1866) I detected evidences of the mighty agent which, ages since, caused the elevation of the many thousands of feet of stratified rocks which are comprised in the Old Red Sandstone, the Carboniferous Limestone, and the Coal-measures of the Mendips. This is visible in a basaltic dyke of considerable thickness emerging from beneath the Old Red Sandstone at East End near Stoke Lane, and also under the Ridgeway, which forms the most elevated part of this line of hills. My attention was directed to the spot by the report that some peculiar minerals occurred there. The dyke was not, however, visible at the surface, and I had to remove the turf at different points, immediately under which it appeared in a deep-green-coloured basalt, all the minutest cracks and fissures of which were permeated by manganese, giving its outer surface a dark purple tinge. From the general physical character of the Mendips, it is not improbable that the dyke is coextensive with the range. East and west of a line of which Stoke Lane forms nearly the centre, for a distance of seven miles there is an uninterrupted anticlinal. The direction of the dyke from East End towards Frome is evidently south of Leigh-on-Mendip, and between that village and Downhead, and thence to Little Elm, a distance of about four miles. It then probably passes through, and has modified, the Carboniferous Limestone of the valleys west of Frome, and has left its last physical evidences at Oldford, a mile north-east of that town, where the Old Red Sandstone is greatly contorted, and disappears in that direction under the Fuller's Earth. |