The quantity shipped from Stockton is on an average about 3000 tons per annum. The whole of the lead mines in Great Britain are estimated to produce from 46000 to 48000 tons per annum.
The minerals which occur in the veins of the lead-mine district are the following.
Ores of Lead.
Crystallized in cubes, or with all the angles or edges of the cube truncated or bevelled in various degrees, or in octohedrons.
Occurs in cavities with fluor, and calcareous spar, pearl spar, quartz, sulphate and carbonate of barytes, iron pyrites, sparry iron ore, blende, calamine, &c.
Crystallized in 14-sided figures, imbedded in soft brown marly clay like umber, which effervesces with acids: from Kilhope mine at the head of Wesrdale.
Reticulated ore from Allenheads and Aldstone moor.
Steel grained ore from the Teesdale, Weardele, Allendale, and Aldstone mines.
Specular ore or slickensides in a matrix of calcareous spar; from Allenheads.
Antimonatied Lead ore.─From Dufton mines.
Lead Ore with excess of Sulphur.─This ore is earthy, of a bluish grey colour, and so highly inflammable as to take tire and burn on being held in the flame of a candle. From Dufton mines.
Carbonate of Lead.─Massive. Colour grey. Lustre adamantine. From Flow-edge mine Aldstone.
In 4-sided tabular crystals, bevelled on the terminal planes: lustre adamantine. From Allenheads and Aldatone moor.