This figure is taken from a hand specimen, and is three-fourths the natural size. If it were supposed to be indefinitely enlarged till each bed of coal was 2 or 3 feet in thickness, it would do equally well for a representation of the interlacing of the larger beds. It must be borne in mind that even the minute scams of coal in the above-drawn hand specimen were not mere carbonaceous matter, but were perfectly bright, good coal; and that little or no difference was perceived in the quality of the coal interstratified with the rock fault, and that of the same beds in the unaffected coal around it.
It is clear from the above facts that this is not a case of any kind of denudation of the coal subsequently to its formation, but that whatever cause produced this mass of interposed sandstone was acting during the time of the formation of the coal. We will, however, defer the consideration of the theoretical inference to be deduced from these cases to a future page.
The occurrence of the "rock and rig" or white sandstone, more or less streaked with coal in the Thick coal at Dr. Percy's pits and the neighbourhood, about a mile to the south-east of Tividale, is one of precisely similar kind to that just described. Great irregularly formed beds of this sandstone come in, over, under, and among the coals there, the coal being sometimes streaked and veined with sandstone layers, and the sandstone having often vein-like layers of perfectly bright coal. In some places there the coal seems to have been partially eroded, and patches of black batt covered by sandstone deposited in the hollows thus formed, in others the two substances were evidently deposited in alternate layers of an inch or two in thickness, the layers of each substance thickening out and coalescing in opposite directions into larger and larger masses.
The whole measures, however, here have been evidently subject to great squeezing and dislocation. They are traversed by faults, and slickenside surfaces are seen in every direction, and sometimes the layers, especially those of coal lying in the sandstone have been bent, and are now tortuous like veins, while masses of the sandstone have likewise indented the coal.
The confusion is further complicated by veins of trap, which are all of a white colour, having intruded into both coal and sandstone, as will be described further on.
Mr. Cooksey, who accompanied me over these workings during the past year (1858), informed me that in driving gate-roads through these masses of intertangled coal, sandstone, and trap, they had met with one or two cakes of unaltered and uninjured Thick coal, of sufficient extent to pay part of the unprofitable outlay in making explorations.[1]
I also, in October 1858, visited the under-ground workings of Messrs. Harper and Moore's colliery at Causeway Green, accompanied by their agent. Mr. Green. The great cake of sandstone, 60 feet thick, spoken of at p. 44, must undoubtedly be an example of a rock fault. We were not then able to examine it, but in some of the gate-roads I observed masses of sandstone lying in the coal, in so remarkable a manner that I made sketches and measured them as accurately as could be done ea ground without greater preparation. These are shown in Figs. 7 and 8.
- ↑ I have been since informed (July 1859) that they have now driven beyond all this "troubled ground" into good uninjured Thick coal without either sandstone or "white rock" trap.
