British Mineralogy . 173 



silver, galena, chalcopyrite, blende, iron pyrites, arsenical pyrites, 

 and quartz. It may be stated here that the crystallized galena 

 in immediate proximity to the rich polytelite contained upon 

 assay only 0*08 per cent, of silver. 



The geological position of this mineral lode is close to the 

 junction of the Cambrian rocks with the Lingula-beds of the 

 Lower Silurian formation. The main lode runs nearly N.W. and 

 S.E., dipping to N.E., and cuts through the Menevian group 

 with its associated diabases : the Paradoxides Davidis is found 

 in abundance in the slates within a few yards of the outcrop of 

 the lode. 



Before concluding this notice of the occurrence of polytelite in 

 Wales, it may not be out of place to add here a few lines on the 

 importance of such an inquiry when considered from a practical 

 or economical point of view. 



Upon reading the report of the proceedings of a meeting of 

 the Tyddynglwadis Mining Company in 1864, a statement will 

 be found, in the agent's report of " surface " operations (p. 15), 

 to the following effect : — " Our slime-pits are very deficient. I 

 would strongly recommend your attention here, because some of 

 these slimes are very rich in gold and silver : the lightest slime, 

 curiously enough, is always the richest in the precious metals." 

 The perusal of this paragraph at once gave rise to the suspicion 

 that the bad results obtained from the dressing-machinery and 

 operations employed by the Company in the treatment of the ores 

 of this mine might in part at least be due to the silver being 

 mainly present in the ore in the state of polytelite (specific gra- 

 vity about 4*8), and not, as previously supposed, contained in 

 the galena (specific gravity 7 '7). This suspicion, corroborated 

 by the small percentage of silver found, as before stated, in the 

 pure galena crystals when assayed, was still further confirmed by 

 the result of the following experiment. 



A portion of the ore, mainly consisting of galena with quartz 

 and a talcose mineral, along with some minute specks of iron py- 

 rites, polytelite, blende, and chalcopyrite, was pulverized, and by 

 the use of a sieve brought to a very uniform powder, which was 

 then carefully washed in a small batea until it was divided into 

 two portions of different specific gravity. 



The most metallic-looking and heavier of these two products 

 appeared on inspection to consist mainly of clean galena, whilst 

 the lighter or more earthy portion would contain all the other 

 substances present in the ore. 



This latter was now submitted to a similar washing, using 

 even more care in so doing than in the former case, and by this 

 means was in its turn subdivided into two products. The smaller 

 or heavier and more metallic portion, when examined with a mag- 



