GEOLOGY OF PART OF SOUTH DURHAM. 



165 



an upthrow, notwithstanding that the reverse is sometimes 

 taught. 



The group of faults shown in fig. 8 occurs in the Five Quarter 

 coal, at Railey Fell Pit, and within a range of thirty yards. 



It is well known that a fault with the hade or plane of dislo- 

 cation going from you is usually a downthrow, and one hading 

 to you an upthrow. There are, however, exceptions to these 

 rules, and the following figures show two that have come under 

 our observation. The one given in fig. 9 occurs in the Brock- 

 well seam, at Railey Fell Pit. On its low side the coal rises to 

 the fracture at six inches to the yard, the hade being outward at 

 45°. These facts would lead a miner to expect that he had ap- 

 proached a downthrow, whereas the coal is thrown four feet up. 



Fig. 9. — Reversed Fault in Broekwell coal, Railey Fell Pit. 



We observed this reversed fault in other parts of the pit 

 named, as the workings advanced. "When first noticed the 

 displacement was only sixteen inches, and when we saw it last 

 it had apparently split up into two reversed faults and another 

 almost with the hade vertical, giving a united throw of five and 

 a half feet. 



The dislocation shown in fig. 10 has been termed an "over- 

 lap" fault, on account of it hading reversely at an acute angle, 

 one portion of the seam of coal being pushed on top of the 

 other. In another part of the pit, about one hundred yards 



