Geologi/ of Coalbrook Dale. 459 



another important but minor line of disturbance. In its course through the coal-measures, where 

 its nature can be advantageously studied in the extensive works at Lightmoor and Madeley, it is 

 known as the " Limestone fault," from the circumstance of its axis being composed of Wenlock 

 limestone and shale. 



This disturbance forms an anticlinal line ; and from the phenomena exhibited in its passage 

 through the coal-measures, it appears that a narrow, central ridge of the subjacent deposits is 

 protruded between the fractured edges of the carboniferous strafa, throwing them off, in nearly 

 vertical dips, but in opposite directions, and producing a change of level, higher, on the N. W. side, 

 by 200 or 300 feet. This disturbance, however, merely affects the position of the strata in its im- 

 mediate proximity; for, at the distance of less than a quarter of a mile on each side, the usual 

 slight dip to the eastward, is unaltered by it, even at the depth of 700 feet. (See Plate XXXVI., 

 sections 15 and 16.) The inclination of the included Silurian strata cannot be well ascertained, as 

 they are much broken. The outcropping edges of the Wenlock limestone, which flank the southern 

 side of this disturbance constituting Lincoln Hill, and Benthall and Wenlock Edges, dip rapidly 

 towards the S.E., and have escaped the denudation which has removed the underlying shale from 

 the centre and N.W. flank of the axis ; wherefore the opposite dips, although very visible in the 

 coal-measures, are not well marked, where the axis traverses the Wenlock shale. 



At Benthall Edge, the centre and the north-western flank of the anticlinal ridge have, by the 

 denudation of the Wenlock shale, been worn into a deep valley. At Tickwood Hill the strata 

 are much broken, and have a quaquaversal dip. The southern prolongation of this anticlinal 

 fault probably produced the well-marked ridge of Wenlock Edge. 



Northward, the Limestone fault is not traced beyond Windmill Hill, but it continues its north- 

 easterly range towards ShifFnall. 



Parallel to, and south-east of this second axis, are several smaller disturbances, producing 

 slight anticlinal lines, which present a central and broken nucleus, a few yards broad, bounded 

 by two parallel fissures, from which the flanking and disjointed strata rapidly dip, and exhibit, 

 as in the preceding instances, proofs of considerable lateral pressure. The first of these small 

 anticlinal lines is about 2|- miles to the S.E. of the Limestone fault, and ranges, by the Upper 

 Ridding, across the Broseley and Bridgenorth road, at the Dean, to Willey and Shirlot. Another 

 anticlinal line exists one mile S.E. of the last, traversing the Ludlow rocks and the lower coal- 

 measures, and is exposed in the brook below Caughley, and near Linley Hall. 



In the preceding cases the disturbing power appears to have acted in a direction nearly S.W^ 

 and N.E. ; but at the northern apex of the coal-field is a short, eruptive axis of trap, partially 

 flanked by Silurian and carboniferous strata, ranging nearly N. by E., and S. by W., and consti- 

 tuting Lilleshall Hill, which rises to the height of 433 feet above the level of the sea. It is 

 bounded on the N.W. side by a large fault, which brings the new red sandstone against the trap 

 and the Silurian rocks and carboniferous limestone. In its prolongation towards the southwest, 

 it joins the Boundary fault, whilst towards the north-east it apparently intercepts, at an acute 

 angle, the Great East fault at Church Aston; and is most probably continued with it into the new 

 red sandstone. 



The abrupt termination of this axis on the south is remarkable. It should intersect the Don- 

 nington field, but we there find the strata in the plane of the axis, and distant from Lilleshall only 

 1^ mile, entirely unaffected by it, and nearly horizontal, with only a few transverse faults ; while 

 as we proceed southward, it again shows itself in the elevation of the central division of the coal- 

 measures of which we have already spoken. Its subsidence northward is equally rapid. 

 VOL. V. SECOND SERIES. 3 O 



