PARALLEL DYKES DISTINGUISHED FROM VOLCANIC GRITS. 275 



trap does not traverse or cut through the adjacent strata, but ranges parallel to their direction. 

 It is not, however, conformably interstratified, but presents an irregular surface and wedge-like 

 form; and further, the mass is not divided into beds divided by joints, but is made up of columnar 

 forms, terminating abruptly against the sedimentary deposits, which, to complete the proof of 

 intrusion of the trap, are highly altered on both sides of it. This dyke is interesting in presenting 

 an example of the alteration of the schists in contact h. Specimens of the porphyritic felspar can 

 be detached with portions of schist adhering to their exterior, almost silicified, some being dark, but 

 passing into a whitish cream, compact clay-stone, resembling porcelain. 



It is arranged in fine laminae in all two or three inches thick, the lamination being occasionally 

 marked by lines of white calcareous spar. This band has a conchoidal fracture, and a surface as 

 smooth as the finest lithographic stone. 



It is in fact the " brand erde " or burnt earth of the Germans, a substance which we 

 know has been formed by the combustion of beds of lignite and coal, producing a long 

 continued heat, which has acted upon the associated shale. In England the most curious 

 actual illustrations of this process are in the South Staffordshire coal-field, particularly 

 in the western suburbs of the town of Dudley, where the spontaneous and long continued 

 combustion of coal in the abandoned mines has produced, in the shale and sandstone, 

 a variety of burnt earths, which are of divers colours, some of them resembling riband- 

 jasper. 



The proofs of the strata having been altered by the heat of this dyke, are conclusive ; for im- 

 mediately beyond this band of china stone, the beds are indurated and somewhat altered to the 

 thickness of about twelve feet, beyond which they pass into a micaceous, sandy, dark- coloured shale «, 

 sometimes slightly calcareous, the unaltered Llandeilo flagstone of the district. Although the beds 

 are hardened both above and below the trap, the overlying strata are the most altered. To the south- 

 south-west, this dyke is lost in the mass of trap hills which terminate in the Corndon, but to the 

 north-north-east it may be traced beyond Leigh Hall, where it finally subsides beneath the low 

 country in the form of an amorphous, coarse concretionary, felspar rock. The concretions sometimes 

 attain the size of a man's head, and being mixed with smaller lumps, the hillock in which they are 

 exposed has quite the appearance, on a superficial glance, of being a pile of drifted matter or "dilu- 

 vium." At this spot it forms the wall of a rich vein of lead ore, which strikes through the shale 

 upon the side of the balls or concretions trap. From the few specimens I obtained, the ore of 

 this vein appears to be of very rich quality, but its extent has not been ascertained 1 . Besides 

 the ores of lead, I observed crystallized sulphate of barytes, iron pyrites, &c. This is the only well 

 authenticated case of a good vein of lead ore having been found so far upon the western flank of 

 the Corndon and Shelve Hills ; for although similar trials have been made on the south-south- 

 western prolongation of this ridge of Whitsborn Hill near Rorington and Little Weston, they have 

 invariably terminated, after much expense, in discovering little more than appears on the surface in 

 many of the natural ravines of the district ; viz., large veins of crystalline carbonate of lime, sulphate 

 and carbonate of barytes, &c. In the neighbourhood of Leigh Hall, are other lines and bosses of 

 intrusive trap. A remarkable one is close to the high road, east of the house and within one 



1 The low level of this situation has occasioned the work to be stopped by water, but it has been recently 

 resumed. 



