456 J. Prestwich, Esq., en the 



Ketley fault produces a change of level between 500 and 600 feet ; but at 

 New Dawley, distant two miles, of only 40 or 50 feet. The Lightmoor fault 

 at Snedshill produces a change of level of 300 feet; at the Dark Lane and 

 Malinslee, of nearly 700 feet; at New Dawley, of 350 feet; at Dawley 

 Green, of 400 or 450 feet ; and at Great Dawley, of 500 feet ; but at Light- 

 moor it diminishes to 300 feet. This variation arises partly from the junction 

 of other faults, but is principally owing to a slight difference in the angle of 

 dip of the disjointed portions of the coal-field. I have mentioned that the 

 edges of the disjointed strata are generally much bent; the bend being fre- 

 quently flanked by a series of small faults. Thus, in the following diagram of 

 the dislocations, on approaching the Ketley fault, near Donnington Wood fur- 

 naces, a series of minor faults is represented flanking the principal or Ketley 

 fault. 



Scale, 150 feet = 1 in. 



The same eff'ects are exhibited in several parts of the Lightmoor fault, and 

 likewise precede the Madeley fault near the Hay House. They were noticed 

 also on approaching the line of the Great East fault at Southall. The ra- 

 pidity of the dip stopped the miners before reaching the main fault. 



The phenomenon of a principal fault flanked by numerous smaller ones, is 

 termed by the colliers " the splitting of a fault." Thus the Ketley fault is said 

 to split upon approaching the boundary fault near Donnington Wood furnaces. 

 (See Map). Whether in this and other cases the side or branch faults result 

 from a temporary and local division of the larger fault, whether they pro- 

 ceed in gradually diminishing magnitude from the large faults, or whether 

 they form a series of small paraflel and independent faults, I have no positive 

 data to prove. I am however inclined to adopt the two latter hypotheses. 



It is rather remarkable, that although the district is so much disturbed, 

 and bosses of trap protrude in many places through the sedimentary strata, 

 yet there is only one instance of an apparently continuous trap dyke. This 

 occurs in the case of the Boundary fault, along which are indications of the 

 proximity of trap, a mass having been met with near Woombridge, and the 

 coal along great part of the line from Ketley to Donnington being converted 

 into smut. This change of coal into a sooty substance has been noticed also 



