a plan of the colliery and with registers of the strata pierced through in sinking the three deepest pits, having also an opportunity of questioning several intelligent miners who had themselves worked in the colliery, and of examining many tons of trap rock and of the adjacent beds which had been brought to the surface, I think that there will be found no material error in the following statement.
The surface of the colliery at Birch-hill (Pl. 12. fig. 1.) somewhat exceeds 83 acres; and is itself only part of a more extensive coalfield, the portions of which adjacent to the present colliery have been worked out so long ago as to preclude the obtaining any correct information concerning them. The ground rises with a very gentle slope on the east, falling nearly flat and becoming marshy on the west. On the south-western edge of the colliery is a low ridge, from 20 to 30 feet above the level of the marshy land at its foot, from 70 to 100 yards broad, and extending along the southern edge of the colliery for 3 or 4 hundred yards, till by degrees it coalesces with the general slope of the land, and is no longer distinguishable. This ridge is named the green rock fault, and forms the separation between the Birch hill colliery and an exhausted one adjacent to it on the south.
There have been about twenty pits sunk at different times, more than half of which are in the south-western angle of the colliery; not one of these has reached the bottom of the coal-formation, and therefore the rock upon which it rests is unknown: I apprehend however (from the general analogy of this part of the country) that the fundamental rock is flœtz-limestone.
