Fig. 25.
Great Bentley Fault.
Scale 6 in. to 1 mile, vertical and horizontal.
1. Old man's coal.
2. Bentley Hey coal.„
3. Heathen coal.„
4. Sulphur coal.„
5. Yard coal.„
6. Bass coal.„
7. Fire-clay coal.
8. Green-rock trap.
9. Bottom coal.
10. Silurian shale, with Dudley and Walsall limestones.
In the trough between these two faults, on the south side of Bentley Heath, they get a nine-foot coal, called the Old Man's coal, which crops out shortly in each direction, as it is never more than 5 or 6 yards deep. The Bentley Hey coal, 5 feet thick, is 50 feet under this; and the Heathen coal, 50 feet under the Bentley Hey. We have already seen that the Old Man's and the Bentley Hey coals mustc, if even only on account of their relation to the Heathen coal, be the bottom beds of the Thick coal separated into two.
The eastern outcrop of the Old Man's coal in the Bentley Trough is just north of the Bentley furnaces, the Bentley Hey coal cropping west of the canal near Birch Hills, and the Heathen and lower coals cropping out successively to the east as we follow the trough towards Ryecroft.
The Great Bentley fault appears to branch towards the east in the manner represented in the map, its branches running up to Rushall and dislocating the measures there, as before mentioned in the description of the Walsall Silurian district. To the northward of the Bentiey Trough, the Bentley Hey coal crops in the bed of the brook (which afterwards forms the little river Tame), north of the Bentley Heath furnaces, and the Heathen coal crops a little to the eastward of that.
These two outcrops run off northward with an undulating line in consequence of slight undulations in the surface and variations in the dip of the beds, for about a mile, the general dip being to the west at an angle of 3° or thereabouts. Several cast and west faults are then met with, the most important of which runs north of the New Invention and south of Bloxwich. This in the centre of its course has a downthrow to the north of 195 feet (65 yards) diminishing, apparently, in each direction. Two little faults, with insignificant downthrows to the south, run between this and Sneyd's Pool reservoir, while one to the south of it running through Herbert's Coppice has a 'downthrow to the south of 45 feet (15 yards) with another very small one to the south of it, having a small downthrow to the north. After being dislocated backwards and forwards by these faults the Bentley Hey coal crops at the south side of Sneyd's Pool, beyond which nothing is known of the outcrop, although the coal itself is met with in the deep sinkings
