Northumberland and Durham. 5 



the breadth from north to south four hundred yards, the depth seventy 

 feet. The beds pass over the ninety-fathom-dyke ; which has oc- 

 casioned 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 nume- 

 rous 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 



