was any solid basalt met with, though one or two strings or tortuous veins of trap seem to have been cut through in the tunnel.[1]
The mass of the rock passed through both in the tunnel and the shaft consisted of a reddish and greenish coloured clay or shale and sandstone, sometimes the argillaceous, sometimes the arenaceous character predominating. The sandstones often contained pebbles, and thus passed into conglomerates. It was only in the upper shafts, those numbered 5, 6, and 7, that the green ashy rock mentioned above seemed to have been got, so far as I was able to judge from an examination of the spoil banks.
The Thick coal has been worked round three sides of these hills, and it appears generally to dip under and pass beneath the basalt. On the north side only, however, has it been followed under the basalt, and that for but a very slight distance; and in every instance in which this has been attempted the coal has been found to be "blacked" and to be fractured, and frequently to pass into "rock and rig." A coal is said in this district to be "blacked" when, by its near proximity to an igneous rock, it has become so altered as to lose all its brightness, and nearly, if not quite, all its inflammability. It is not exactly coke, but is dull and earthy, and on exposure to the atmosphere is very friable. It frequently in this state contains small nodular concretions of iron pyrites. I have never had the opportunity of examining a pit where the coal was thus affected, except Mr. Percy's pit, now belonging to Dr. Percy, at the Grace Mary colliery, a little east of Rye Cross Farm. Here, at a depth of about 200 yards, they came into blackened coal, penetrated by long dykes of white rock trap, and more or less intermingled and mixed up with white sandstone. This white sandstone was full of little patches and shreds of coal, and the coal was frequently entangled in the sandstone, and the two mixed up together in a very singular way. This kind of sandstone is that called by 'the colliers "rock and rig" In one of the gate-roads of this colliery the white trap ascending from the floor, or descending from the roof, cut both into the coal and the sandstone, in the manner shown in Fig. 13.
Fig. 13.
a The white-rock trap.
b The coal.
c White sandstone (rock and rig).
This was drawn to scale with a measuring tape, and is sufficiently accurate representation of the facts. A little north-west of this part of the mine a fault was met with, beyond
- ↑ Mr. Walker, jun., who superintended the works of this tunnel, was good enough to let me see a large section constructed from the workings, from which the above statements were taken.
