1869.] HULL GEOLOGY OF CHESHIRE. 173 



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 omis- 

 sion 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 Eamsay to the agency 

 of ice. These beds were separated by the author in this district, as 

 well as in that of Stafibrdshire, from the overlying Bunter Sandstone, 

 and are described by Professor Eamsay in his memoir " On the 

 Evidences of Permian Glaciers," published in the Journal of the 

 Society f. The same beds reappear on both sides of the South Stafi'ord- 

 shire coal-field, and are described in Mr. Jukes's memoir " On the 

 Geology of the South Staffordshire Coal-field" J. 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 Coal- 

 field." 



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 



* This calcareous breccia is only, as Sir R. Murchison shows, a local deposit, 

 derived for the most part from the disintegration of a limestone belonging to 

 the upper coal-measures. It cannot be considered a representative of the Per- 

 mian Limestones of the North of England. 



t Vol. ii. p. 185. 



I Mem. Geol. Survey. 



