Geology of Coalhrook Dale. 457 



at Madeley, near the Hay House. For an account of the effect of the trap 

 rocks, see ante, p. 449, et seq. 



The faults cannot be traced by any modification of the surface; as they 

 pursue their course indefinitely over hill and through dale; and those towering- 

 irregularities, due immediately to the convulsions, powerful effects of which 

 are still attested by the fractured and shattered strata, have been leveled and 

 swept away, leaving scarcely a trace of their presence. 



It must, however, be observed, that, although the masses of strata do not re- 

 tain their original superficial inequalities, as effected by the dislocations, yet 

 these disturbances have materially aided in modifying the outline of the coun- 

 try, by bringing to the surface, rocks of different degrees of hardness, which 

 having yielded very variously to powerful denudations, great diversity of hill 

 and dale has been produced. 



The " Symon fault" not being the result of fracture, is treated of under 

 the head of lithological characters. (See p. 432.) 



Having taken considerable pains to trace the faults of this district, I am 

 able to describe them in some detail*. To avoid minutiae, however, I have 

 arranged them, as far as possible, in a tabular form ; and all dislocations of 

 less than 20 feet of difference of level are, with few exceptions, omitted, as 

 well as in the sections and plans. (See Appendix D.) 



The two principal faults, called the Lilleshall and the Great East, diverge at an angle of about 

 20", a little south of Newport, and bring up a wedge of the Silurian and carboniferous rocks into 

 horizontal juxtaposition with the fractured edge of the new red sandstone. After ranging south- 

 ward nearly four miles, a central axis of disturbance intersects longitudinally the included coal- 

 measures, and divides them into three distinct systems, each bounded by prolonged and nearly 

 parallel lines of fissure, ranging between the limits of N.E. and S.W. and N.N.E. and S.S.W., 

 and called the Boundary, Ketley, Lightmoor, and Great East faults. The two exterior systems 

 constitute at first deep troughs. This trisection of the coal-field forms a very marked feature in 

 the VVoombridge and Ketley districts; but as we proceed southward the depth of the eastern 

 system of beds, compared to that of the central, considerably increases, and in the same district the 

 western becomes nearly as shallow as the central. Thus the coal-measures in the western and 



* The following observations are much more ample than those contained in the memoir read 

 February 1834, which presented a short sketch of the principal faults. I have now added further de- 

 tails respecting their range, connection and effects. In detecting these disturbances I received great 

 and valuable information from the miners; but, owing to their experience being confined to small 

 areas, they are, with few exceptions, unable to trace the range of any fault. Although, therefore, 

 1 have taken every care in dovetailing these several fragments, slight inaccuracies in the exact 

 course and termination of some of the minor faults may exist. Where considerable doubts liave 

 been entertained, I have omitted the information altogether. The courses and magnitudes of all 

 the larger and more important disturbances are, I trust, laid down correctly. 



