Geologi/ of Coalbrook Dale. 453 



deeper seated coals and ironstones have been discovered and rendered avail- 

 able. 



Previously to describing' the range of the faults, I will briefly explain their 

 nature and characters. The edges of the disjointed strata are generally in 

 contact, or are separated merely by a layer, a few inches thick, of clay, fre- 

 quently nearly white. The fractured surface is usually striated or ribbed ver- 

 tically ; and, where this layer of clay is wanting, the coal, as well as the bitu- 

 minous shale, presents highly polished surfaces. In some parts of the field, the 

 colliers have " black and white slips" or very small faults, which cross at va- 

 rious angles. The black, which are almost always parallel to the main face of 

 the coal, present smooth and polished surfaces, whilst the white slips contain a 

 thin layer of clay. To this point I shall again refer. The inclination of the 

 faults appears to obey no general law, varying in the range of the same fault 

 from 45° to 90°. For instance, Mr. Jones of New Hadley found that the 

 horizontal distances in the uppermost and lowermost beds of coal between the 

 shaft of a pit near Potter's Bank and the line of the Ketley fault, were equal, 

 and consequently that the fault was perpendicular. This fault is, in other 

 places, considerably inclined. When the sides of the fissure are perpendicular, 

 they are commonly separated several yards, sometimes as much as forty or fifty, 

 the interval being filled with broken debris of the strata. Generally, however, 

 the sides of the fissure, instead of having been forced asunder, have been 

 strongly compressed. In most cases the edges of the strata are turned up- 

 wards on the side of the lower level, and downwards on that of the higher, or 

 in the expressive language of the colliers, " the measures rise to a rise, and 

 dip to a swamp*." There are a few rare instances, however, of the reverse. 

 The following diagrams exhibit examples of small faults or slips in the lower 

 coals. (For examples on a larger scale, see Sections, Plate XXXVI.) 



Hill's Lane pits, Madeley. Madeley pits. Holywell pits, Malinslee. Holywell pits, Malinslee. 



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A good instance of lateral pressure is exhibited in the following wood-cut, 

 taken from a Section in the Holywell pits, Malinslee. 



* The phraseology of the colliers with respect to faults is extremely convenient. The whole 

 district situated upon the higher side of a fault A is said to be on the rise of fault A; and the 

 whole of the district on the lower side is said to be " in the swamp." Thus, in fig. 5, a is on the 

 rise of fault A, or simply " on fault A" ; h is in the swamp of ditto : stratum a' dips to the swamp 

 of fault A ; stratum h' rises to the rise of ditto. 



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