GEOLOGY 



got coal, which has made Birmingham and Wolverhampton the great 

 hardware manufacturing centres of the world. 



The Dudley Coalfield has been regarded as the typical area for the 

 Middle Coal-measure flora of Great Britain. The genus Sphenopteris in this 

 sub-division attains its maximum development. Stumps of the gigantic 

 lycopod, Lepidodendron, have been met with in such profusion in the 

 workings of the Parkfield Colliery as to form a veritable fossil forest. 

 As in North Staffordshire the commonest mollusc is Carbonicola (Anthra- 

 cosia). In addition to remains of fishes the coalfield has also yielded 

 specimens of Arachnida and insects, types rare or unknown in North 

 Staffordshire. All these fossils, excepting the Fishes, indicate the close 

 proximity, if not the absolute presence, of land ; but below the Thick 

 Coal, fossils such as Lingula, Productus, Discina and Pterinopecten show 

 a temporary incursion of the sea ; though these marine episodes do not 

 appear to have been of such frequent recurrence as in the north. 



Upper Coal Measures. The gradual infilling of the basin and final 

 change in the character of the sediments, accompanied by the gradual 

 passing away of the fauna, is as clearly illustrated in the southern part of 

 the county as it is in the Potteries. In the districts of Corngreaves and 

 Oldhill the ordinary grey Coal-measures graduate upwards into a con- 

 siderable thickness (over 300 feet) of red clays (Red Coal-measure Clays of 

 Jukes) indistinguishable from the Etruria Marls of the northern coalfield. 

 Moreover they contain similar thin bands of ashy green grits known as 

 ' Espley Rocks,' As the area is not far distant from the Cambrian and 

 Pre-Cambrian ridges of the Lickey Hills, these green grits, as might be 

 expected, contain angular fragments of the Lickey rocks. Occasionally 

 the grits are so coarse as to form a true breccia, interesting as fore- 

 shadowing the breccia conditions so prevalent in the succeeding 

 ' Permian ' rocks of South Staffordshire. The red clays afford some of 

 the material for the famous South Staffordshire blue bricks, and large 

 quarries have been opened round Oldhill. 



The brick clays pass up near Halesowen (just beyond the county 

 limits) into grey sandstones and marls (Halesowen Sandstone Group], about 

 400 feet thick, containing an occasional thin seam of coal and a well 

 marked band of Spirorbis limestone near the summit. These in turn are 

 surmounted, quite conformably, by red sandstones and marls, generally 

 included in the ' Permian ' formation, but identical with the Keele type 

 of North Staffordshire. 



The sequence of the Upper Coal-measures of North Staffordshire 

 is thus at once seen to be repeated around the southern margins of the 

 South Staffordshire Coalfield, and the connection of the two fields 

 either absolutely, or at least as regards the similarity in the sequence 

 of events proved beyond dispute. The same sequence too has been 

 detected in the deep sinkings and borings outside the exposed coalfields, 

 where the green ' Espley Rocks ' at once afford the miner a clue to his 

 position in the Coal-measure sequence. 



Origin of Coal. As the county abounds in this mineral a few words 

 i 17 3 



