bed below becomes thin, this coal swells out to 3 feet for a short space, while at High Bridge, where the swelling out of the bed below to 9 feet takes place, the coal thins again to 1 foot 9 inches. The deposition, like all other aqueous depositions, was evidently thicker where there was a hollow, and thinner where there was a rise,in the bottom. South of this point where the intermediate bed ceases altogether, the united coal layers continue southwards with a uniform aggregate thickness of 7 feet. Returning to the Rising Sun we find over the Roof coal (which together with the coal below and the intervening bed is spoken of there as the Deep coal) an accumulation of shales and sandstones varying greatly in the details of their grouping and thickness even in closely adjoining pits, but making an aggregate thickness of 41 feet 3 inches in one pit, and 48 feet 10 inches in another. This is in each case covered by the series of layers of coal called the Shallow coal, having an aggregate thickness of 6 feet. At Pelsall Wood the Shallow coal is only 4 feet thick, while the beds between it and the Deep coal are 45 feet, but at High Bridge the coal is 5 feet 2 inches, and the beds below are only 37 feet 9 inches.
From this point the two coals retain their thickness of 5 feet and 7 feet as they range southwards, but the beds between them rapidly thin out, and finally disappear about a mile and a half south of High Bridge. The two coals then come together to form a twelve-foot coal, and continue under the name of the Bottom coal with that thickness for a mile or two to the southward, when they also begin to get thinner and thinner, and finally die out in the district south of Dudley.
This instance, of which the details could be traced, if necessary, through various contiguous collieries in far greater detail, is only one instance of the many similar changes occurring throughout the Coal-measure series. These changes are distinctly referable to the action of water in transporting materials of different kinds that have been committed to it, and cannot, so far as I can see, be referred to any other agency.
If we look at the diagrams on Plate I., with the knowledge of these and similar facts fresh in our minds, and not with the view of extracting a merely possible explanation of it from conceivable circumstances, I think we cannot fail to be struck with the obvious "delta-like" or "bank-like" form which the Coal-measures of South Staffordshire must have originally possessed, and the perfect resemblance they must have had to an undisturbed subaqueous accumulation.
It seems to me then impossible to suppose otherwise than that the whole series of the Coal-measures, coals included, were deposited by one connected operation of the same forces acting in obedience to the same physical laws on similar but slightly differing materials, through an indefinite but immensely long period of time.
