depth they came on a little "lean" ironstone, which was conjectured to represent the Blue flats.
43. The base of the Coal-measures.—It remains now only to investigate the nature and thickness of the beds that lie below the Blue flats and other ironstones, or, where those measures are not present, the lowest beds of the Coal-measures in each locality.
I may premise, that in the cutting of the railway near Trindle Gate, just east of Dudley, the base of the Coal-measures was very well exposed, resting on the Silurian shale, and exhibiting the following facts.
The Coal-measures here consisted of pale yellowish sandstones, many of them argillaceous (rock binds), with some small beds of shale or clay. The Silurian shale was a compact blue shale in thick beds, lying very regularly in a nearly horizontal position. At one part of the section some of the upper beds of the Silurian shale ended in a moderately sloped cliff, against which the sandstone of the Coal-measures abutted, while they reposed on the lower beds of shale that continued beneath them. As both groups of beds were nearly horizontal, no unconformity could be perceived between them, except just at the little Silurian cliff. Here the lamination of the sandstones became oblique, trying to conform to the slope of the cliff, and the lower beds of it, both near the cliff and for some yards back, contained pebbles and many small angular fragments. 'The pebbles were mostly white crystalline quartz, with some rolled pieces of ironstone. The angular fragments were chiefly Silurian shale and limestone. 'The cliff was about 20 feet high (see Fig. 11.)
Fig. 11.
a Coal-measuresb Silurian shale.
From this very instructive instance we learn generally how, with perfect apparent local conformability, there may be still on the large
