490 



DUDLEY PORT LIMESTONE BENEATH THE COAL. 



a mass of limestone which proved to be nearly seven yards thick, of exceedingly fine 

 crystalline quality, and less argillaceous than most of the limestone of this tract. On 

 excavating laterally to the south and east, or away from the fault, the limestone was 

 found to extend more or less horizontally, and hence it became an object of prompt 

 speculation, both from its convenient position, and from the excellent quality of the 

 material. When I visited this mine, though the works had only been in progress a few 

 months, they had already cleared out a subterranean chamber of about 100 yards 

 square, and about seven yards in height, supported by rude columns of limestone, the 

 " ties" of the workmen. On descending, I found a large company of miners excavating 

 and exploding the solid rock in a chamber filled with dust, and into which not one drop 

 of water percolated ! This appeared the more surprising, since the coal-field which had 

 previously been worked out above our heads, was saturated with copious streams of water 

 descending from the adjacent Rowley Hills. This fault, like most others, is from its 

 compact structure a dam to water, and the shafts being sunk in it were necessarily dry, 

 while the limestone occupying a horizontal position, and being covered by argillaceous 

 shale, the bavin of the workmen, we can easily imagine how the interposition of such 

 impervious materials should close up all access to this excavation ; or in other words, 

 how the waters of the superjacent coal-field should flow above it, supported by the shale 

 of the Silurian rocks. 



On " stripping " the fault towards the trough, the limestone was found to be in contact with a 

 seam of coal which was squeezed downwards, and its surface, as well as that of the limestone, pre- 

 sented the polished slickensides, so frequently observed in similar cases. This coal was supposed by 

 Mr. Downing (who accompanied me in this examination) to be the fire clay coal of the same age 

 as that of Stourbridge, one of the lower beds not usually worked in this part of the district. The 

 portion of the side of this fault which I saw, ranged 15° N. of E., but as the general direction of 

 the sides of the great Dudley trough is nearly N.E., S.W., this must have been one of those zig- 

 zag aberrations so often observed along lines of fractures. Near the fault, the limestone dipped 

 slightly N.N.E., but on being followed on the dip, this inclination even decreased, the beds gradually 

 assuming a dome-like form, into which they are brought by a succession of very small hitches. At 

 the last discovered of these downcasts, the limestone was beginning to incline from 12° to 15°, and 

 as this inclination was too rapid to permit further work upon the dip, it was supposed that a new 

 shaft would soon become desirable. The limestone extracted for burning is subcrystalline, and 

 finely laminated, with rarely any wayboards of shale thicker than a flat ruler, and hence forming 

 two beds only. Both are of gray colours, and are made up of a profusion of encrinites and shells. 

 The rock, indeed, is so compact, that holing places for the gunpowder are found with difficulty, and 

 hence the mining operations are attended with some expense 1 . Having ascertained the lateral 

 extension of this limestone over the area of their property, the successful speculators next bored 



1 The quantity of gunpowder used, when I visited the spot, was half cwt. per diem, and as masses of thirty 

 tons were brought down at a blast, the effect produced was sufficiently sonorous. The dead silence which 

 followed these explosions was quickly succeeded by the din of voices and the clatter of pickaxes. Ventilation 

 is effected by means of air heads driven through the fault. 



