2)6 MurcMson's Silurian System. 



Longnor, Uffington, Longdon, Le Botwood, Pitchford, &c, where it is 

 evident from the nature of the sides of the trough, and also by the 

 shallow depth at which the Silurian and Cambrian rocks are met with, 

 that no coal can exist, further trials would be absurd. 



" An examination, however, of the country on the south bank of the 

 Severn, has convinced me, that coal may be profitably extracted to a 

 certain extent in the tract lying between the Pontesbury and Asterley 

 coal-pits, and the escarpments of the dolomitic conglomerate, and 

 lower red sandstone of Cardeston and Alberbury. Trials in this dis- 

 trict or in the adjoining tract, south-west of Cardeston, could be made 

 at small expense, it being highly probable that if the coal measures are 

 not cut off by the rise of older rocks, which is discountenanced by the 

 form of the country, they are only covered by the thick accumulation 

 of gravel and argillaceous clay which overspreads this depression. At 

 the same time that we give apparent good reasons for finding the thin 

 or upper coal strata within a limited area, it is fair to state, that prac- 

 tical observation militates against the supposition of any great expan- 

 sion of coal beneath the lower new red sandstone on the right bank 

 of the Severn. In no one of the present works does it appear that the 

 seams of coal become thicker, or increased in number, when followed 

 downwards on the dip. And although these trials have hitherto pro- 

 ceeded to so short a distance, that no very decided conclusions can be 

 drawn, yet it must be allowed that they weaken the supposition of the 

 thin or upper coal-measures graduating downwards into richer fields. 

 We might, indeed, surmise that this zone of coal, which judging from 

 the nature of the limestone, was probably accumulated in a lake or 

 near the mouths of rivers, has merely resulted from a very partial accu- 

 mulation of vegetable upon its shores, and that beyond the drift or range 

 of these small gatherings of wood we should look in vain for a mineral 

 formed out of such materials. It might also be said that as these car- 

 bonaceous zones of the plain of Shrewsbury differ so essentially from 

 the largely productive tracts of coal in the absence of the underlying 

 deposits of carboniferous limestone, millstone, grit, &c, we ought rather 

 to presume, that the mineral thus wanting in its accustomed associa- 

 tions would be fully developed, On the other hand, it may be con- 

 tended, that according to analogies elsewhere, carbonaceous matter 

 formed upon the natural edges of such a basin would naturally thicken 

 towards its centre; or, in other words, that as a certain amount of 

 vegetable matter had been accumulated upon the shores of these anci- 

 ent rocks, still larger quantities were probably washed down their 

 shelving sides into the depths of a capacious bay or estuary, on the 

 opposite limits of which we actually meet with other and highly pro- 



