Geology of the Harz Mountains. 241 



mines have now reached a depth of 400 fathoms, and the ore 

 shows no signs of disappearing. Those of St Andreasberg 

 are, however, nearly exhausted, and although considerably- 

 deeper than the Clausthal workings there is little hope for 

 their future productiveness. 



The Clausthal veins contain argentiferous galena, blende, 

 and copper pyrites, with spathic iron, calcspar, quartz and 

 barytes as veinstones. Quartz and spathic iron occur in all 

 the veins of the Clausthal plateau, but it is a curious fact 

 that calcspar is only found in the area to the JST.E. of the 

 Innerste valley, while barytes is confined to the veins tra- 

 versing the south-w^estern and western . portions of the 

 district. 



The veins are all in fault fissures which run E. and W. 

 through the Culm strata, and usually hade to south. In 

 some cases the downthrow exceeds 100 fathoms. The ore is 

 distributed in the veins in various w^ays. It is usually in 

 diagonal bands (Erzfalle), which slope towards the west, but 

 occasionally occurs in columns or vertical ribs running paral- 

 lel to the direction of hade. Besides the minerals just men- 

 tioned the veins contain smaller quantities of such minerals 

 as dolomite or pearlspar, iron pyrites, marcasite,fahlerz or grey- 

 copper, bourn onite, heteromorphite, etc. The ores are usually 

 richest where two of the larger veins meet and merge into 

 one another. They sometimes reach a thickness of 130 ft., 

 and generally contain a considerable quantity of fault breccia 

 made up of fragments of the adjacent greywackes and shales. 

 The foot wall is, as a rule, sharply defined from the vein, 

 but the hanging wall is usually shattered and rough, so that 

 the exact thickness of the vein cannot always be accurately 

 stated. 



The Andreasberg veins are almost all situated within an 

 area resembling a very obtuse isosceles triangle with a base 

 about 4 kilos in length. Two sides of the triangle are barren 

 fault fissures (faule Euscheln), full of fragments of clay slate 

 and shale, with a southerly hade, and a breadth sometimes 

 reaching 200 feet. None of the silver veins pass out of the 

 area thus enclosed. All the outsiders are base, containing 

 only copper pyrites and ironstone. 



VOL. VIII. Q 



