able to the formation of sandstone and the accumulation of clay, but unfavourable to the formation of coal. The extension of this "rock fault" and old Silurian bank is at present uncertain; it appears, however, either that they extend continuously for three miles to the south of West Bromwich, or that they recur at that distance near Langley Green, as we shall see hereafter when describing the boundary faults.
We have in these facts, then, an instance of the unconformity of the Coal-measures both to the Silurian below and the Permian above; and it is probable that a little further east of the Heath pits the Coal-measures are entirely wanting, and the "red rocks" of the Permian formation rest directly on the shale or "bavin" of the Silurian formation. This would then be one of those cases where the denudation of the Coal-measures had proceeded the length of totally removing that entire series of rocks previously to the deposition of the Permian beds. The whole history of the Heath pits gives us a good example of the value of geological knowledge to the practical miner; Ist, assuring him of the general fact of the existence of coal beneath the "red rock" of the Permian and New red sandstone formations; 2nd, putting him on his guard as to the possibility of coming down to a spot where the coal had been removed by denudation, showing him what he might expect as possible as well as what was probable, and teaching him what to do in any case.
We have now to examine the original relations between the New red sandstone and the Permian. - These two formations seem likewise to be unconformable to each other, but we cannot yet exactly ascertain either the amount or the precise method of this unconformability. The possibilities of the case are,—
1st. After the partial denudation of the Coal-measures the Permian rocks may have been deposited, not uniformly over the whole district, but in large patches here and there, filling up hollows, but leaving bare the higher spaces of older rock. On this surface the New red sandstone might be deposited, resting sometimes on the Permian, sometimes directly on the Coal-measures, or perhaps on still lower rocks.
2nd. The Permian, after having filled up and levelled the old hollows in the Coal-measures, was continued, as to its upper beds, over the whole district. In that case those upper beds must have been again more or less denuded, as we now find the New red sandstone resting sometimes directly on the Coal-measures without the intervention of any Permian rock whatever.
This is the case at Brereton near Rugeley, where they have sunk in several pits through the quartzose gravel or conglomerates of the New red down into the Coal-measures, the two lying distinctly in an unconformable position, the coals cropping gently up into the base of the New red.
After attaining the New red sandstone there appears no further occurrence of unconformability, the beds appearing to lie with perfect parallelism and regularity through the red sandstones and gypsiferous marls up to the Lias of Needwood Forest.
