356 STRATIGKAPHICAL GEOLOGY 



This Lower sandstone attains its greatest thickness (650 feet) 

 near Bridgenorth, but is still about 400 feet near Chester. It 

 ranges northward to the Mersey and then east- 

 ward along the southern border of the Lanca- 

 shire coalfield, but thins in that direction, and 

 does not occur at Manchester or Stockport. More- 

 over, it appears to thin out in every other direc- 

 tion, for, though it is found in places on the west 

 side of the South Staffordshire coalfield, it does 

 not appear on the east side. Southward, again, 

 it extends to Stourport, and is probably con- 

 tinued underground as far as Worcester, but is 

 V, 'x .st! overlapped in every direction by the succeeding 

 [! 1 | Pebble Beds. 



Clearly, therefore, this sandstone was accumu- 

 lated within a restricted area, which was prob- 

 ably a desert plain, bounded on the west, south- 

 east, and east by higher ground, but possibly 

 reaching for some distance to the north-west 

 c below the Irish Sea. 



The Pebble Beds. These beds are most 

 fully developed in East Shropshire and South 

 Staffordshire. They pass eastward beyond the 

 outcrop of the Lower sandstones, resting uncon- 

 formably sometimes on the Permian, sometimes 

 on the Coal-measures, as in Cannock Chase (see 

 Fig. 116). In this central area they form a mass 

 of conglomerate which is from 300 to 400 feet 

 thick, and consists of well-rounded pebbles, the 

 majority of these being brown and chocolate- 

 coloured quartzites, with which, however, are 

 pebbles of Carboniferous limestone and sandstone, 

 of purple grit, and of some volcanic rocks. At 

 the surface the sandy matrix is generally soft, 

 ^ but when traversed in deep borings it is very 

 f\ J hard and highly calcareous. 



~ a s Near Bridgenorth it has a breccia of angular 



111 -a fragments at its base about 60 feet thick, but 

 "3 g 8 this does not seem to extend far. It recurs, 

 however, at Holt, on the river Dee, where it 

 is succeeded by soft red-streaked sandstone over- 

 lain by pebbly sandstone, the whole series 

 resembling that at Bridgenorth. Near Liver- 

 pool and St. Helens they attain a great thickness. 



