212 Murchisoris Silurian System. 



" In this spot the limestone is no longer worked, but it has been 

 reached beneath the last mentioned bed of coal, which is therefore 

 proved to be the uppermost of the three seams before mentioned. In 

 sinking to the limestone, the shafts passed through a course of small 

 concretions of calcareous clay iron stone, called 'Rattlers,' in which 

 I observed nests and coatings of mineral pitch, and veins of white cal- 

 careous spar. This may represent one of the thin Manchester lime- 

 stones. There being no natural denudations in this district, it is only 

 from an occasional trial shaft, like this, that I have had any opportunity 

 of judging of the precise structure of the beds passed through, and it is 

 therefore probable that in the section at Pontesbury and in other parts 

 of this coal-field, the overlying strata may contain other thin courses 

 of impure concretionary limestone which have escaped the notice of the 

 miners, and if so, the analogy between the Shropshire and Lancashire 

 beds may be still more complete, even to agreement in mineral charac- 

 ters. This portion of the field is indeed exceedingly dislocated, it 

 being difficult to find a spot exceeding a few yards in width, in which 

 the strata are not full of faults. This is specially observable on the 

 sides and slopes of Lyth hill, the promontory of purple greywacke 

 or Cambrian rock which has been alluded to, and which, as we shall 

 shew, is penetrated in many points by trap rocks. Between Lythwood 

 and the brook at Wellbatch, a distance not exceeding half a mile, 

 there are four principal upcasts upon the dip of the strata, the greatest 

 of which is a rise of forty, the least of about eight yards. It is to 

 be remarked, that, here the beds are inclined to the north-west, 

 sloping away from the Lyth hill promontory, so that between the 

 coal works at Coedway and these near Shrewsbury the coal strata 

 dip on three sides towards a common centre. The coal which is worked 

 at Uflhigton, three miles north-north-east of Shrewsbury, is a beau- 

 tiful illustration of the manner in which this zone, following the 

 sinuosities of the more ancient rocks, reappears at intervals upon 

 their flanks, for there the same purple Cambrian sandstone as in 

 the Longmynd, Lyth hill, &c. (the most ancient rock in this region 

 and underlying the whole of the Silurian system) rises in an insulated 

 mural form, constituting Haughmond hill. The little patch of coal 

 measures occupying the low ground between that hill and the river 

 Severn, contains the usual fresh water limestone of the district, asso- 

 ciated, however, with one seam only of workable coal, as proved by the 

 folio wine section : — 



