Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/267

1869.] this type are those of a more or less local deposit, of which the marginal limits during deposition may in some places be traced. Towards the north-west, we first find these beds along the eastern boundary of the Denbighshire coal-field at Wrexham, and in the valley of the Dee, near Overton. South of the Severn, they reappear near Cardeston and Alberbury, where, with the remarkable calcareous breccia which there forms an important (but exceptional and local) feature, they were originally described by Sir R. I. Murchison in the 'Silurian System.' We trace the same beds (with the omission of the calcareous rock, which disappears eastward) along the northern margin of the Le Botwood and Shrewsbury coal-fields, and again in greater force to the east of that of Coalbrook Dale. From this district they stretch southwards along the valley of the Severn, and in the district of Enville spread out over a large area, and are diversified by calcareous conglomerates and trappoid breccias, the origin of which has been referred by Professor Ramsay to the agency of ice. These beds were separated by the author in this district, as well as in that of Staffordshire, from the overlying Bunter Sandstone, and are described by Professor Ramsay in his memoir "On the Evidences of Permian Glaciers," published in the Journal of the Society. The same beds reappear on both sides of the South Staffordshire coal-field, and are described in Mr. Jukes's memoir" On the Geology of the South Staffordshire Coal-field". Crossing the Triassic district to the east of Birmingham, they are found to emerge from beneath the Keuper Sandstone and Marl, and to occupy a large tract of country lying to the west of the Warwickshire coal-field, where these beds were surveyed by Professor Ramsay and Mr. H. H. Howell, and are described by the latter in the Memoirs of the Geological Survey, "On the Geology of the Warwickshire Coalfield." Along the west and the south of the Leicestershire coal-field we again find these beds, but in disconnected and attenuated masses, evidently the marginal representatives of the great formation of Warwickshire. In this district is clear evidence that we have reached the original limit of the lower Permian beds towards the north-east, and that we stand on the confines of the barrier of Carboniferous rocks which divided the Permian rocks of the North of England from those of the midland counties.

Along the southern and western margin of the North Staffordshire coal-field, the lower Permian beds again appear interposed between the coal-measures and the New Red Sandstone. When traced northwards for some distance, they are lost to view at Madely, partly through the overlapping of the Bunter Sandstone, partly through attenuation. Nor do we find any representatives of the