CHAPTER VII. 

 COAL-FIELD OF COAL BROOK DALE. 



Upper Coal and Freshwater Limestone. — Lower Coal or productive Coal and 

 Iron field. — Carboniferous Limestone. — Trap Rocks and Dislocations. 



FROM the thin and slightly valuable carboniferous tracts around Shrewsbury we now 

 proceed to the consideration of the great productive coal-field of Shropshire, in which 

 are found nearly all the members of the carboniferous system. Geologists owe their 

 earliest knowledge of this coal-field to an interesting memoir by Mr. A. Aikin, published 

 twenty-six years ago in the first volume of the Geological Transactions 1 ; and recently 

 a fresh mass of most instructive and curious information respecting it has been brought 

 forward by Mr. Joseph Prestwich. As soon as I found that the last-named geologist 

 was assiduously studying the structure of this remarkable district, I willingly referred 

 all details to his enterprise, being aware that the region over which my inquiries ranged, 

 was too large to permit of minute attention being paid to the intricate relations of this 

 highly dislocated tract. To his forthcoming memoir in the Geological Transactions I 

 therefore refer such of my readers as may require precise detailed knowledge, confining 

 my own observations chiefly to the general features of the carboniferous strata and their 

 relations to the surrounding deposits. 



Occupying both banks of the Severn at Madeley and Broseley, the principal and most 

 productive portion of this field spreads out to the north of that river in a large trian- 

 gular-shaped mass, the apex of which terminates at Lilleshall. (See Map.) To the 

 south it is flanked by the Old Red Sandstone and upper Silurian rocks ; to the west by 

 a thin zone of the lower Silurian rocks and by the trap rocks of the Wrekin and Ercal 

 Hills. Throughout more than two thirds of its circumference, i. e. to the north-west 

 and east, this tract is bounded and overlaid by the Lower New Red Sandstone ; but the 

 passage from the coal measures into that formation is not so clear as in the Shrewsbury 



1 Mr. A. Aikin had prepared a vast quantity of geographical data, illustrating the structure of this tract, 

 which he lent to me. With his permission I subsequently placed the maps in the hands of Mr. Prestwich, 

 who has made an excellent use of them. His inquiries commenced after I had pointed out the stratigraphical 

 and zoological distinctions between the carboniferous and Silurian limestones of this neighbourhood, (Steer- 

 away, Lilleshall, Wenlock, &c.) 



