PRACTICAL HINTS CONCERNING THE SHREWSBURY COAL-FIELD. 95 



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 conglo- 

 merate, and Lower Red Sandstone of Cardeston and Alberbury. Trials in this district 

 or in the adjoining tract, south-west of Cardeston, could be made at small expense, it be- 

 ing 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 practical observation militates 

 against the supposition of any great expansion 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 proceeded 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 accumulation of vegetables 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 

 carbonaceous zones of the plain of Shrewsbury differ so essentially from the largely pro- 

 ductive tracts of coal in the absence of the underlying deposits of carboniferous lime- 

 stone, millstone grit, &c, we ought rather to presume, that the mineral thus wanting in 

 its accustomed associations would be feebly developed. On the other hand, it may be 

 contended, 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 ancient 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 productive coal-fields rising from 

 beneath a cover of New Red Sandstone. I do not throw out such suggestions as an 

 inducement to proprietors, north of Shrewsbury, to endeavour to penetrate the thick 

 and massive deposits of which the overlying New Red System is composed ; although 

 it is by no means impossible that a coal-field may there lie hidden, which when the 

 more accessible coal strata in other tracts shall have been exhausted, may prove of 

 value to future generations. Such an inference is rendered more probable by the obser- 

 vations in the next chapter, which show, that a band of coal measures of the same age, 

 passing similarly upwards into the New Red Sandstone, and containing a limestone iden- 

 tical with this of the Shrewsbury plain, distinctly overlies the edges of the most productive 



m 2 



