Besides the green-rock fault, already mentioned, there is another which passes through the colliery longitudinally in a direction E. by S. and W. by N. This fault is a mere dislocation of the strata causing a depression of 72 feet to the S.: a smaller fault or Rider branches off nearly due W. from the larger one causing a further depression of 4 feet in the strata which lie immediately to the S. of it. The junction of these two faults takes place precisely under the Furnace.
The beds on each side of the central fault rise nearly S. at an angle of about 6°; but, in the immediate vicinity of the green-rock fault, the second coal and all the beds lying above it (as far as they have been explored) are thrown up at an angle so rapidly increasing as, in the space of about 100 yards, to amount to 25°.
None of the beds are known to vary materially in thickness except the trap. The thickness of this latter in the Engine pit and in the Bye pit amounts to 24 feet, but in the pit B it is diminished to 12 feet, and in the pit D which is sunk down to the third coal the trap is wholly wanting. The miners themselves conclude from these facts, and apparently with reason, that the bed of trap is merely a great wedge from the green-rock fault which has intruded itself between the proper coal strata, but is by no means co-extensive with them.
To the geologist the circumstances connected with the relative situation of the trap and with the state of the beds that lie immediately above and below it are of singular interest; and it happens fortunately that the two most interesting of these beds, namely the indurated sandstone and the blind coal, have been explored to the distance of several yards. This was effected in driving a heading for ventilation from pit A to the pit B, see section Pl. 12, fig. 2.: this heading was begun in the first or yard coal, but on passing the
