252 Mr. AiKitJ on a Be J of Trap 



a plan of the colllevy and v.'ith registers of the strata pierced through 

 in sinking the three deepest pits, having also an opportunity of 

 questionifig several intelligent miners who had themselves worked 

 in the colliery, and of examining many tons of trap rock and of 

 the adjacent heds which had been brought to the surface, I think 

 that there will be found no material error in the following state- 

 ment. 



The surface of the colliery at Birch-hill (PI. 12. fig. 1.) somewhat 

 exceeds 83 acres ; and is itself only part of a more extensive coal- 

 field, 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 

 iand 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) th^ 

 the fundamental rock is floetz-limestone. 



