Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/87

 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 (occasionally) 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 speaking 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