254 Mr. AiKiN on a Bed of Trap 



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° j 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 increas- 

 ing 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 imme- 

 diately 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 PI. 12, fig. 2. : 

 this heading was begun in the first or yard coal, but on passing the 



