WR. E. WILSON ON THE DURHAM SALT-DISTETCT. 773 



strike of the non-conformable Permian and Triassic rocks. Some- 

 times the rock-salt is entirely wanting, but in none of the deep 

 salt-borings, colliery-sinkings, or more superficial excavations into 

 the Magnesian Limestone of Durham have any saliferons beds ever 

 been found associated with any undoubted Permian rocks. 



Area of the Salt-Jldd^ Limits of Distribution and Depth of the 

 Hock-salt. 



The question naturally arises at this point, Can we at present 

 form any conception of the extent of the area of the Durham 

 Salt-field ? All experience in other salt-districts shows that this 

 mineral does not, like coal, lie in continuous beds of pretty uniform 

 thickness over very extensive areas, but that it is liable to rapid 

 fluctuations and sudden total disappearances. This evidently applies 

 to the South-Durham salt-field. As we have seen, the thick salt-bed 

 was present at Middlesborough in full development (100 feet). At 

 Messrs. Bell's Saltholme trial-boring, three quarters of a mile to 

 the north, the bed was reduced to little more than half this thickness 

 (65 feet) ; at the Newcastle Chemical Co.'s boring on the Tees, only 

 three quarters of a mile west of these two points, the salt-rock had 

 entirely run out. At Stone Marsh, about a mile further west, the 

 rock-salt is present, but in a very attenuated condition ; whilst at 

 the equally distant Haverton-Hill borings it attains its maximum 

 development in the district. 



Again, at the Greatham boring, midway between Middlesborough 

 and Hartlepool, the salt is present in full thickness ; but at Seaton 

 Carew, a little over two miles north of this point, it is absent. In 

 the seven wells put down by the Newcastle Chemical Co. on the 

 Tees-mouth shore, the salt-bed was found to vary from 90' 6" to 

 115' 4", i. e. 24' 10" in a distance of only 132 yards, a fluctuation at 

 the rate of 1 in 16. Evidently, then, the bed consists of one or 

 more * great lenticular masses. 



There is little reason to doubt that in this form the salt-bed has 

 a wide distribution beneath the estuary of the Tees and the bordering 

 districts. It is fuUy developed at the Greatham boring on the north 

 and at the Ormesby boring on the south, places four miles apart, and 

 has so far been met with in good thickness at every exploration in 

 a straight line between the two points. In a transverse direction 

 (W.N.W. and E.S.E.) the salt-rock has been found well developed 

 from the Eston Ironworks to Haverton Hill, a distance of very 

 nearly three miles. How far the bed extends from the Greatham 

 boring towards Seaton Carew can only be proved by actual sinkings ; 

 but its absence in the recent Seaton and earlier Oughton borings 

 seems to indicate that there is a considerable Triassic area bordering 

 the Magnesian Limestone country which is destitute of this mineral. 

 As regards the southerly extension of the rock-salt, the ample 

 development of the thick bed at points between two and three miles 



* It is assumed as most probable that the thick salt-bed hitherto met with 

 in the various deep borings in this district is one and the same bed. See Vertical 

 Sections, facing p. 782. 



