Northumberland and Durham. 77 



and between them fine grained sandstone is the predominant rock. 

 The basalt at Embleton is black and coarse grained, and it breaks 

 into angular masses. The latter circumstance renders it useful for 

 the construction of walls and houses, and for the lining of limekilns ; 

 though it is commonly quarried for mending roads.* 



In the crevices by the sides of basaltic veins strings of lead ore 

 are frequently observed, but these are never known to pass through 

 the dykes. 



The fissures which contain lead ore in the mining district are exactly 

 similar to those described by Williams in his Mineral kingdom- 

 Such as range from north to south are called cross veins, or (occa- 

 sionally) dykes; they are generally of great magnitude, and seldom 

 carry ore; the most valuable mineral depositories are fissures from 

 3 to 6 feet wide, running for the most part from south-east to 

 north-west, and cutting the cross veins ; the cross veins being 

 frequently rendered productive to some distance from the points of 

 intersection. 



The same vein is productive in different degrees at different 

 depths according to the bed which it traverses. Generally speak- 

 ing veins are most productive between the grindstone sill and the 

 four-fathom limestone ; none have been worked in Aldstone moor 

 below the level of the Tyne bottom limestone; but the Dufton 

 mines are situated in the lower beds, though none are worked in 

 the Melmerby scar limestone. 



The limestones are the chief depositories of ore, particularly that 

 called the great limestone, which is considered to have produced as 

 much lead as all the other sills together. Next to the limestones 



* A basaltic dyke has been observed on the coast at Beadnel passing from the south- 

 east to the north-west, of which a description as I understand has already been given to 

 the Society by the Hon. H. G. Bennet. (See the following Paper.) 



