Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/88

 the strata of sandstone called hazles are the most productive of ore; but the lead-bearing veins appear compressed between these hard sills. In Arkendale the sills of chert yield considerable quantities of galena, but this rock does not occur in the mining field further north. In Shale the veins are comparatively barren, and in traversing these soft strata weak veins hade considerably.

The hade of the veins is variable in degree, and in direction. When the veins in Weardale point east and west, they hade towards the south; but in Allendale and in the Aldstone moor country they generally hade towards the north: the strata are universally elevated on the side towards which the veins dip.

Veins, that are otherwise favourably circumstanced for producing ore, are more particularly so if the throw or alteration in the level of the beds of limestone, occasioned by the vein, does not exceed 1 or 2 fathoms; for then both cheeks of the vein correspond in their nature, and limestone does not become opposed to shale or other barren stratum.

The following are some of the most remarkable veins in the mining district.

At Burtree—ford, where an alpine brook first assumes the name of the river Wear, a very strong vein, called the Burtree-ford dyke, crosses the mining field from north to south, and passing on the west side of Allenbeads cuts off or at least terminates all the valuable veins discovered in that mine. This must not be confounded with the basaltic dyke which passes the river at Burtree a little above the cross-vein. In some situations this fissure appears to elevate the strata above 80 fathoms on the eastern side, and in others greatly to depress them, as may be observed at the quarries in the great limestone not far from Allenheads. Contiguous to the dyke the sills rise at an angle of 45°. Practical miners have remarked