:6 TMr. N. J. Winch on the Geology of 



iron become of a brick-red colour. Considerable quantities of fuel 

 are found necessary at the kiln, and some parts of the rock are too 

 apt to vitrify in the process, an accident to which the crystalline 

 limestone of Sunderland is not liable. 



Along the coast of Durham from Shields to Hartlepool, the 

 .uppermost bed frequently consists of a species of breccia, the cement 

 of which is a marl-like substance consisting chiefly of magnesian 

 carbonate of lime, and with this breccia wide chasms or interrup- 

 tions in the cliff are filled. The next strata are thin and slaty, but 

 lower down the stratification becomes less distinct. The colour 

 of this rock is then light hair brown, the texture crystalline and 

 cellular, from which latter cause it strongly resists the stroke of the 

 hammer. The slaty variety occurs at Bolden hills, Marsden rocks, 

 and numerous other places j its colour is white inclining to buff; 

 dendritical marks may be found between the thin layers into which 

 it easily breaks ; and in Marsden lane and on the sea coast a flexible 

 icind has lately been noticed by Mr. Nichol. In the neighbour- 

 hood of Sunderland* the brown variety is generally quarried ; it 

 partakes of the nature of swinestone, and from containing some 

 inflammable matter requires only a small quantity of coal to be 

 reduced to lime. That worked at Denton, not far from the Tees, 

 and analyzed by the Rev. J. Holme, is, I suspect, of this quality, 

 for he mentions bitumen, as one of its constituents ; whereas Sir 

 H. Davy takes no notice of that substance in the rocks of Eldon 

 and AyclifF. 



* The exportation of lime from Sunderland is chiefly to Scotland, and amounts to from 

 forty-two to forty-uye thousand chaldrons of 36 bushels each, annually. 



