Page:The South Staffordshire Coalfield - Joseph Beete Jukes - 1859.djvu/151

Rh produced. Or, lastly, with all respect to my friend Mr. Blackwell's acuteness of observation, (which no one will be more ready to acknowledge than I, who have so often profited by it,) he may have been led away by appearances which in the imperfect light of underground workings might have deceived any one. It seems to me quite possible that portions of the consolidated basalt may have been squeezed for some distance up into the fissures, and still more likely that some of the more decomposed parts (the clay or wacke, which often forms the covering of the hard rock) may have been so squeezed, at least as far as it was possible to follow it in underground explorations.

Whatever may be the exact state of the case with regard to this particular instance, the larger and more general fact remains undoubted, that there is no relation whatever either of cause or effect between the igneous rocks of the coal-field and the principal dislocations that have affected it; and that the igneous rocks all existed in and among the Coal-measures very much in their present condition before any of the great dislocations were commenced.

 

assume the conformability among themselves of the several members of the Silurian formation in South Staffordshire. This is rendered probable by their conformability in the neighbouring district of Shropshire, and there is no evidence against it in Staffordshire. Starting with that assumption, we must necessarily conclude that before the Coal-measures were deposited the Silurian beds had been slightly tilted at one end, namely, on the eastern side, and made to dip towards the west, and that their surface had suffered considerable denudation. The uppermost member of the Silurian formation, the Ludlow group, is only found on the western side of the main part of the 'coal-field. If we draw a nearly north and south line, starting from Ettingshall Park farm, running between Hurst Hill and Sedgley Beacon, and continue it down through Cradley to the south, we find that to the west of that line, wherever the Silurian reels rise to the surface, namely, at Sedgley, at Turner's Hill, and the Lye Waste, they consist of the Ludlow or upper division; while all to the east of that line, wherever the Silurian rocks rise to the surface, or have been reached by shafts through the Coal-measures, they consist of the Dudley and Wenlock division of the upper Silurian series. The farther we go east, moreover, from this line, the more nearly do the Dudley limestones rise into proximity to the Coal-measures and to the surface, until at Walsall they crop broadly out, and the shales below them still rising gently to the 