Fig. 7
Scale, 8 feet to 1 inch.
The mass of sandstone shown in Fig. 7 was about 18 feet long and 5 or 6 feet high. It was of a pale greenish grey colour, fine grained, principally quartzose, with a little argillaceous matter mingled with it. It occupied parts of four beds of coal, but although laminated throughout and marked here and there with dark carbonaceous streaks, or even little seams of bright coal, it did not seem itself to be separable into four beds, nor was there any distinct plane of stratification (distinct from the lamination) visible in it. Its form was as nearly as possible that given in the sketch, the indentations being as sharp and angular as there drawn. The thinning and arching of the coal over the thickest part of the sandstone was very noticeable.
Fig. 8
Scale, 4 feet to 1 inch.
Fig. 8 is a similar sketch, taken in a neighbouring part of the same gate-road, drawn on twice the scale. 'The principal mass of sandstone was about six feet long, with a smaller mass of two feet at one corner. The sandstone extended through three beds of coal, but was more separated by rather irregular planes of stratification than that seen in Fig. 7.
Many other masses of pale sandstone were to be seen in the coal on each side of these gate-roads, while in some places the whole coal seemed mottled and streaked with flakes of sandstones. It was especially remarkable that the thin seams of coal interstratified with these sandstones, seemed even brighter and purer than the main mass of the coal, where it was without any interlacing of arenaceous layers or masses.
Rolls, Swells, &c.—The second peculiarity of structure in the Thick coal is that which forms those irregularities, called "horse's backs," "rolls," " swells," "pack-saddle faults," &c. These are caused by a rise of the floor of a coal up towards the roof, in such a manner as to form a long arched ridge running through the coal, sometimes for a very considerable distance. I examined one of these in the Baremoor colliery, when visiting
