468 



VOLCANIC GRIT OR TUFACEOUS CONGLOMERATE. 



subject, being connected with the lines of dislocation along the frontier of the coal field, 

 will be resumed towards the conclusion of the next chapter. I will here only remark, 

 that in the shaft of Lord Dartmouth and the other situations alluded to, the Lower New 

 Red Sandstone has been affected by all the dislocations which have disturbed the coal 

 measures, and that the two formations are everywhere in conformable position, both at 

 high and low angles of inclination. 



Volcanic Grit or Tufaceous Conglomerate. 



Besides the shale and sandstone common to all coal fields, this tract is distin- 

 guished by containing a peculiar grit, frequently tinged green; the " Espley rock" 

 or "Blue rock" &c. of the colliers. It occurs in moderately thick strata in the 

 central portion of the field between West Bromwich on the east and Kings Swinford 

 on the west. In the southern district, however, i. e. south of the Netherton Canal, 

 it expands to vast thicknesses, and there forms the connecting link between the 

 coal measures and the Lower New Red Sandstone. On exposure it weathers to 

 dingy yellow, red and green colours 1 . The round topped hills of Haydon, which 

 are formed of it, may be taken as a centre, from whence it extends to the southern 

 end of the Rowley Hills, and all over Gorsty Hill through the district ranging from 

 Hales Owen by Corngreaves and Homer Hill to Cradley. This rock is briefly alluded 

 to by the Rev. J. Yates (Geol. Trans, vol. ii. p. 253.) and called a trap tuff, but neither 

 its relations to the productive coal measures nor to the other trap rocks have been 

 pointed out. From the vast quantity of trappean matter in its composition, I have no 

 hesitation in considering it a variety of volcanic grit, and as it alternates in many beds, 

 both with the Lower New Red Sandstone and the upper strata of the coal measures, 

 there can be little doubt that it was formed from the detritus of submarine volcanos, 

 which were in activity towards the close of the accumulation of the coal measures. It, 

 therefore, exhibits vestiges of the earliest volcanic action traceable in these parts ; for in 

 the sequel we shall show that the other trap rocks of this district (Rowley Hills, Barrow 

 Hill, Pouk Hill, &c.) instead of having a depositary character, have all been intruded 

 forcibly into the strata after their consolidation, because they dislocate and break up 

 the coal measures together with the volcanic grits under consideration. All the shaft 

 sections in the neighbourhood of Corngreaves pass through great thicknesses of this 

 grit 2 , which may also be studied in natural sections in the deep ravines of that pictu- 

 resque and hitherto little worked portion of the coal-field which ranges from Gorsty 



1 See the dotted tract on the map extending from Hales Owen to Netherton and the south end of the Rowley 

 Hills. 



2 See section, No. 3. p. 477, of the principal shaft of the Corngreaves works, obligingly given me by Mr. Best, 

 director of the British Iron Establishment. In this case I examined the specimens brought up from the original 

 sinkings. 



