458 J, Prestwich, Esq., on the 



central divisions gradually thin off, until, in the parallel of Little Wenlock, they entirely crop out, 

 after a range of 9 miles. Within the same range the eastern division increases in breadth and im- 

 portance, but its continuity is for a short distance completely broken by the limestone fault, which 

 crosses it diagonally from S.W. to N.E., and tilts up this division of the coal-measures to the 

 westward. (See Map, and Section 8.) 



After crossing the Severn the same eastern division widens considerably, but it is much broken 

 and elevated by a series of transverse fissures, some of which are parallel to the limestone fault, but 

 others are at right angles to it. In consequence of these dislocations the coal-measures gradually 

 and irregularly crop out, and the Silurian rocks are brought to the surface. 



The above systems of longitudinal disturbances are affected by numerous small transverse faults, 

 which, proceeding from one of the principal dislocations, sometimes extend across to another, 

 but more often gradually diminish in their range, and disappear. These transverse fractures 

 diverge from the main longitudinal ones at all angles ; but the larger commonly at 90°. In the 

 deeply seated strata of the northern portions of the coal-field, their number is comparatively small; 

 but in the parallel of the igneous axis of the Wrekin they are extremely numerous. At Langley, 

 Lightmoor, and Madeley, they are of rare occurrence ; and again, as we proceed south over the 

 Severn to the edge of the coal-field, they become very numerous. 



Returning to the western system we find it gradually rising towards, and ultimately, obliquely 

 intercepted and thrown out by, the mineral axes of the Wrekin and Steeraways, which we will now 

 consider. The Wrekin is a long knife-edged mountain, ranging from S.W. to N.E., and rising 

 to a height of 1320 feet above the level of the sea. It is formed by a central ridge of igneous 

 rocks, flanked by the lower Silurian deposits. Its length, including the Ercal and Primrose 

 hills, is three miles, and its breadth is about two-fifths of a mile. Towering high above the 

 disturbed district, of which it forms the main axis, and still higher above the surrounding and 

 extensive tract of new red sandstone, it constitutes a fine isolated and conspicuous object. 



Parallel to the major axis, and on the north-west flank of the Wrekin, are evidences of a very 

 large fault, by which the disjointed edges of the new red sandstone are brought into contact 

 with those of the lower Silurian rocks. The latter are seen to dip rapidly to the foot of the 

 Wrekin and Ercal hills ; and although we meet with no section exhibiting their juxtaposition 

 with the new red sandstone, still, from the circumstance of having found this deposit in a well 

 on the farm close to the foot of the Wrekin, dipping but slightly towards the north, and again 

 to the north-east, near Eaton Constantine ; and, from the specimens dug out at the foot of the 

 Wrekin, indicating that the beds there do not belong to the lowest members of the new red 

 sandstone, and likewise from the formation ranging in a nearly straight line parallel to the 

 Wrekin, and not extending into the transverse slopes and glens, I think we may fairly infer the 

 existence of a very considerable dislocation west of the Wrekin, and into which the Boundary 

 fault merges somewhere at the northern extremity of that igneous axis. Again, as we know the 

 coal-field to be fractured, and its level, with regard to the new red sandstone, greatly altered, 

 both on its eastern side and on its north-western, from Lilleshall to Steeraways, at which point 

 commence the igneous axes of the Steeraways and Wrekin ; it follows, that as the coal strata are 

 disturbed relatively to the new red sandstone in the parallel of Woombridge, so, in the parallel of 

 the Horsehays, to the east of the Wrekin, where we trace the prolongation of the same disturb- 

 ance in the coal-measures, the relation of the carboniferous series to the New Red Sandstone 

 must continue the same ; and that, though separated by the Steeraways and Wrekin hills, the 

 terminating planes of both those formations must be fractures. 



Nearly parallel to this axis of eruption, and at the distance of 3i miles to the S.E., ranges 



