Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/15

Rh the breadth from north to south four hundred yards, the depth seventy feet. The beds pass over the ninety-fathom-dyke; which has occasioned in them no confusion or dislocation; so that there can be little hazard in stating that the beds of the magnesian limestone belong to a more recent formation than those of the Coal-field. The limestone has been quarried across its whole breadth, and a numerous set of thin strata are thus exhibited to view. At the surface loose blocks of bluish grey coralloid limestone, the produce of the lead mine district are found imbedded in the soil. Three or four of the uppermost strata of the quarry are of white slaty limestone, which being nearly free from iron, burns into a pure white lime. Below these an ash-grey fine grained stratum is met with, which strongly resembles a sandstone, and seems to contain nearly as much iron as the ferri-calcite of Kirwan, becoming magnetic by the action of the blow-pipe: it produces a brownish yellow lime, less esteemed for agricultural purposes than the former. The beds next in succession are of an ash-grey colour, are compact in texture, and conchoidal in fracture: these afford a buff coloured lime, which sells for nearly the same price as the white. Near the bottom of the quarry the limestone alternates with shale; the whole rests upon a stratum of shale on the southern side, and upon a thick bed of sandstone on the northern. The shale has been cut through to a considerable distance from the kilns in the direction of North Shields, for the purpose of laying a rail-way to the Tyne. The thickness of the limestone strata varies from three or four inches to as many feet. Small strings of galena have been found here, and, in one of the strata that was walled up when I visited the quarry, a few organic remains have been noticed.

The stone intended to be burnt is detached from the rock by the agency of fire, during which process those portions which contain