though dark inquiry, will, however, again arrest our attention.
Extent of British Coal Fields under superior Strata.—Disturbances of the Carboniferous System.
To what extent the relative level of land and sea was disturbed during the period which elapsed in the production of the carboniferous rocks cannot be known: to judge from the universal conformity of all the strata which compose it, and the rarity of coarse conglomerates (except at the base of the system), it might appear that no considerable displacement of the crust of the globe happened any where near the British Islands, during the whole carboniferous period. Yet the occurrence of a marine conchiferous bed among the estuary or freshwater strata of the Yorkshire coal field, seems absolutely to require the admission of considerable disturbing movements at a distance.
After, however, the deposition of this whole system, and before, at least, any considerable part of the next (magnesian system) was laid upon it, the scene was totally changed, and the carboniferous rocks of the British islands broken and contorted by subterranean movements of an extensive and complicated description. Every coal field in these islands is remarkably dislocated by faults, often traversed by rock dykes, sometimes ridged or furrowed by anticlinal or synclinal dips, which cause great trouble and expense to the coal worker, and call forth all the resources of his art. Into the history of these disturbances we shall only enter, so far as to present a fair basis of comparison with physical theories. One of the most remarkable great faults or dislocations yet known in the world belongs to this period; viz. that great and continuous fracture of the earth's crust from Cullercoats, near Newcastle, westward along the valley of the South Tyne to Brampton; thence southward to Brough, Kirkby-Stephen, Dent, and Kirkby-Lonsdale; and afterwards eastward to near Grassing-
