454 



J. Prestwich, Esq., on the 



Generally, however, the strata on the sides of the small slips are not much 

 contorted. The above instances (2, 3, and 4,) are more commonly appli- 

 cable to the larger faults, as in 5, The following section of the "best coal" 

 along a level at the Meadow pits, Madeley, shows the prevailing character of 

 the small disturbances. 



Sometimes, owing apparently to the greater hardness of certain strata, the 

 line of fracture assumes a step-like form, as in the annexed r. 



diagram 7, taken in the lower coal level at Priorslee. Where 

 two slips have met, singular effects have been occasionally 

 produced, as in diagrams 8 and 9 taken in the Hill's Lane 

 pits, Madeley. No. 8 is situated in the best and clod coals, and No 

 little flint coal, and is on a larger scale than the other diagrams. 



9. 10. 



6 ^ 



9 in the 



These disturbances are difficult to account for : a, a' appear to be masses 

 subsided or fallen into a wedge-shaped fissure, enlarged probably at the mo- 

 ment of disturbance by the increased separation of b and c, so that a' would 

 fall into the cavity and crush down the seam of coal as in No. 9. 



The intersection of two faults occasionally presents the phenomena in dia- 

 gram (10). 



A small fault or slip usually commences by a simple fracture, accompanied 

 by a slight difference of level between the two dislocated sides ; but the 

 difference rapidly increases, until the smaller fault joins a larger fault (see 

 Map, PI. XXXV., also a, Diagram 1 1, page 455). Thus the Arleston fault, 

 which commences between New Hadley and Ketley as a simple fracture, at- 



