( 77 ) 



On the most important fault called by Uijlenbroek the "Geul 



Valley fault" lie the mines Fosse j, near Hergenraed (Rhenish 



Prussia), Moresnet (neutral territory) and Bleiberg (Belgium). Excepting 



the contact seams, containing calamine, the ores are galena, being 

 the oldest formation as usual, zinc-blende and pyrites. The vein, 

 found at Bommerig mure than 50 years ago in the lowest stratum 

 of the productive carbon, shows that from the south-east to the 

 north-west the mes seek more and more the younger strata ') and 

 that the direction of the Geul vallev fault begins to deviate more 

 towards the north-north-wesl after Bleiberg. 



For years numerous borings were made in a more northern 

 part of Limburg, which led to the sinking and working of some 

 coal-pits. In December 1905 Mr. L. Ruttkn at Utrecht found on 

 the dump of the mine "Carl" 2 ) some pieces of ore which he presented 

 to the Mineralogical-Geological Institute at Utrecht. Further investi- 

 gations, undertaken by him, showed that these ores originated from 

 a vein, met when sinking the shaft, at a depth of 278 metres, but 

 of which the dip and direction had not been lelermined. He 

 succeeded in securing a number of pieces, belonging to private 

 people.. The vein has onlv a thickness of 0.20 M. On the clav- 

 COntaining salband pyrites has deposited, while the vein mass proper 

 consists of calcile, developed in the cavities in the form id' crystals, 

 on which sometimes also crystals of pyrites are found. Beside this 

 vein ores were also found, likewise on joints of the sandstone 

 of the mini' "Carl", namely pyrites, but also zinc-blende, copper, 

 pyrites, and galena. Moreover crystals of calcile are always found 

 and generally dolomite. 



In the mine Oranje-Nassau, near Heerlen, similar formations seem 

 to occur, at any rale crystals of calcile, covered with pyrites, are 

 found here on joints. Peculiar is here the regular coalescence, 

 caused by the small cubes of pyrites accumulating at the poles, then 

 continuing themselves on the obtuse edges of the scalenohedra and 

 here gradually disappearing. 



We finally point out that while in the Stolberg district the veins 

 of galena, pyrites, zinc-blende, and calcite are siill mostly bound to 

 the carboniferous limestone these minerals occur in the more western 

 Worm district on joints of the carboniferous sandstone, which is 

 a more recent horizon, a phenomenon which repeats itself at Heerlen. 



u At Eupen they still occur in the devonian system. 

 2 ) Situated at l 1 /» kilometers east of Heerlen. 



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