MEMOIRS OF THE GEOLOGICAL SURVEY ENGLAND AND WALES. go. But geological survey PART III. THE COUNTRY AROUND CARDIFF, BEING AN ACCOUNT OF THE REGION COMPRISED IN BY AUBREY STRAHAN, M.A., F.G.S., AND T. C. CANTRILL, B.Sc. PUBLISHED BY ORDER OF THE LORDS COMMISSIONERS OF HIS MAJESTY'S TREASURY LONDON: PRINTED FOR HIS MAJESTY'S STATIONERY OFFICE, And to be purchased from E. STANFORD, 12, 13, AND 14. LONG ACRE, LONDON: HODGES, FIGGIS, AND CO., 104, GRAFTON STREET, DUBLIN; From any Agent for the sale of Ordnance Survey Maps; or through any PREFACE. This volume, which forms the third part of the Memoir descriptive of the geology of the South Wales Coalfield, illustrates the country around the principal town connected with the coalfield and the chief outlet for its products. The map (sheet 263) of which it forms the explanation was originally surveyed about the year 1840 by Sir H. T. De la Beche with the assistance of W. T. Aveline; but additions, chiefly in the Secondary Rocks, were made in 1872 by H. W. Bristow and H. B. Woodward. The re-survey on the six-inch scale was carried out during the years 1892-6 under the superintendence of Mr. Strahan, who himself surveyed the greater part of the sheet, while Mr. Cantrill was engaged upon the western part of it. The following pages have been written mainly by Mr. Strahan, but Mr. Cantrill has supplied the descriptions of the area surveyed by himself. The oldest strata, consisting of Ludlow and Wenlock rocks, come to the surface near Cardiff in the axis of a great anticline of pre-Triassic age. Their existence was first detected by the Rev. Norman Glass in 1861, but it was not until 1879 that their extent and age were placed beyond doubt by Prof. W. J. Sollas. Much information concerning them was obtained at a later date also by Mr. John Storrie. The Old Red Sandstone presents the same general features as in Monmouthshire, and the precise position of the boundary between Upper and Lower Old Red Sandstone still remains doubtful. The Carboniferous Limestone is concealed for the most part by later rocks, but is evidently far thicker on the southern than on the northern side of the coalfield, as is the case with all the subdivisions of the Carboniferous system. Among the most interesting features of the geology is the partial uncovering of a pre-Triassic landscape by the denudation of the Trias and Lias from parts of the platform of Paleozoic Rocks upon which they were deposited. Not a few old head-lands and islands have thus been brought to light, and some are even playing the same part in the present sea-scape which they played in Triassic times; all of which facts received full recognition from De la Beche. In the examination of the Rhætic Beds and Lias the surveyors have availed themselves of the detailed work of H. W. Bristow, R. Etheridge, and H. B. Woodward, and of the additions made to it by Mr. John Storrie and Mr. F. T. Howard. Superficial Geology is well illustrated in the neighbourhood described in these pages. The raised beach so well known round the shores of the Bristol Channel, exists near Weston-super-Mare, and the suggestive observation of Mr. E. C. H. Day as to the age of the bones contained in it have received confirmation from recent observations in Gower, where the beach and its associated 5233. Wt. 5156. 500-8/02. Wy. & S. 6. head a |