GEOLOGY OF PART OF SOUTH DURHAM. 



163 



Faults. — The principal faults that affect this part of the Dur- 

 ham coal-field are noticed afterwards (p. 185). Connected with 

 them are many minor dislocations, a few of which we figure in 

 the following woodcuts. 



Fig. 6.— Fault in the Brockwell coal, Railey Fell Pit. 



Fig. 6 exhibits a fault of the common type, hading nearly at 

 45° to the plane of the seam, with a throw of four feet nine 

 inches. The coal is six feet thick, and good in quality close up 

 to the fracture on both rise and dip sides. The roof is fine dark 

 grey shale, with the planes of bedding beautifully polished or 

 "slickened" for twelve yards or more on the high side of the 

 fault, but not on the lower side. The strata rise to the fault on 

 its high side, and dip to it on its low side as is usual. 



Fig. 7.— Fault in Brockwell coal, Railey Fell Pit. 



Fig. 7 represents another fault of larger magnitude than the 

 last, hading at nearly the same angle, but with the coal much 

 broken-up on its high side, while on the other it is unaltered. 



The manner in which strata abutting against a fault are af- 

 fected by the dislocation is a subject worth investigating. It 

 often happens that the coal, roof, and pavement on one side of 



