UPPER COAL MEASURES OF SHREWSBURY. 



8i 



rocks, which, as before stated, will be described towards the end of each chapter to 

 complete the geological survey of the tracts in which they are found. 



I have further endeavoured to explain the probable origin of the central coal-fields, 

 by observations scattered through the sixth, seventh, and tenth chapters, and particu- 

 larly at the conclusion of the eleventh chapter, in which we take leave of the carbo- 

 niferous tracts of Shropshire. 



I, Upper Coal Measures and Freshwater Limestone, (b. of wood-cut, p. 67.) 



By inspecting the map it will be seen, that the ancient rocks which compose the 

 Silurian and Cambrian Systems, ranging from Pembrokeshire on the south-west, termi- 

 nate on the north-east in a succession of promontories, more or less parallel, and of 

 unequal lengths, which form the southern, western, and eastern limits of the plain of 

 Shrewsbury. These promontories are fringed by a narrow, broken, and devious zone 

 of coal measures, extending from the Breidden Hills on the west, to the Wrekin on the 

 east, the base line or lower edge of which, is determined by the headlands and bays of 

 the ancient rocks. Sometimes, indeed, the carboniferous strata are so completely 

 isolated by these protruding inferior masses, that they consist rather of a number of 

 patches than of a continuous band. By this disposition, the coal measures repose un- 

 conformably and successively, upon rocks of various ages, from the flanks of which 

 they dip away ; and where not obscured by overlying drifted materials, they are seen 

 to graduate upwards into the Lower New Red Sandstone, passing at slight angles of 

 inclination beneath that formation. (PL 29. Figs. 3, 4, 5, 7 and 9.) The surface of a 

 large portion of the plain of Shrewsbury is represented in the annexed view, the various 

 ridges in the distance being composed of Cambrian, Silurian and Trappean rocks. 

 The low country consists of New Red Sandstone and coal measures, for the most part 

 overspread by a great thickness of gravel and detritus. Let us first examine the portion 

 of this tract which is productive of coal, and lies between the north-eastern termi- 

 nation of the Breidden Hills and Shrewsbury. The principal outcrop of the coal is in 

 a semicircular bay, of which Shrewsbury and Coedway are the eastern and western ex- 

 tremities, and the intermediate places where it has been worked, are Nobold, Wellbatch, 

 Aston, Pontesbury, Minsterly, Westbury, Woolaston and Braggington ; at most of 

 which places the strata have only a slight inclination towards a common centre. It has 

 already been stated, that the lowest strata of the overlying red sandstone at certain 

 points in this district are in contact with, and in some instances graduate into the coal 

 measures. This passage is seen at Wellbatch, Asterley, and Coedway. In these 

 situations the coal measures rest on one side against ridges of older rocks, and on the 

 other, dip in perfect conformity beneath the Lower New Red Sandstone. (See PL 29. 

 fig. 5.) From the arrangement of these beds, as seen near Nobold, where the New 

 Red Sandstone dips to the north-west, conformably with the inclination of the coal beds, 



