CHAPTER XI. 



CARBONIFEROUS SYSTEM {continued). 



Coal-field of Oswestry (North Welsh Coal-field), including Coal Measures, 

 Millstone Grit, and Carboniferous Limestone. — Concluding Observations on 

 the Origin of the Salopian Coal-fields. 



On the Coal-field of Oswestry. 



Although this coal-field is in Shropshire, it is quite distinct from the other car- 

 boniferous tracts of that county, described in the previous chapters, and constitutes in 

 reality the natural southern termination of the great coal-field of North Wales. 



The carboniferous deposits with which it is connected, extend by Chirk and Ruabon, 

 expand into the rich coal-field of Flintshire, and everywhere repose upon a thick girdle 

 of carboniferous limestone which separates them from the older rocks of the Princi- 

 pality 1 . Productive coal measures are only developed at certain spots along this zone. 

 The following brief sketch of the little field of Oswestry is given because it lies within 

 the geographical boundary of the annexed map ; the Silurian rocks of Montgomery- 

 shire being here terminated, and their edges overlaid by the strata of the carboniferous 

 system. In this, as in other coal tracts, the strata will be described in descending 

 order. (See Map and Section, PL 30. fig. 14.) 



Productive Coal Measures (b. of coloured Section, PL 30. fig. 14.).— The portion of 

 the Oswestry field which is productive of coal is very limited, occupying a small area 

 between the town of Oswestry and the hills of Llanvorda, Trefonen, Treflach, and 

 Sweeny. It contains only two seams of coal worthy of extraction, the upper being 

 four feet thick and of tolerably good quality ; the lower six feet is of comparatively 



1 The full description of the other parts of this calcareous zone and the overlying coal measures will pro- 

 bably he published by Professor Sedgwick, who has investigated that part of the country, so interesting from 

 the complexity of its derangements and the great wealth of some of its metallic veins. 



S 



