226 Notices of Memoirs — D. Forbes' 



chalybite, and calcite. The characters of the mineral itself are as 

 follows : massive ; opaque ; lustre metallic ; colour brown -black ; 

 streak black to brown-black ; fracture sub-conchoidal, uneven, and 

 granular, brittle; powder black; hardness, 3*5, scratching calcite, 

 but not fluor ; specific gravity, 4-97. Analysis led to the following 

 numbers : sulphide of silver, 15'67 ; sulphide of antimony, 34"82 ; 

 sulphide of copper (Cu S), 34*26; sulphide of iron, 7-57; sulphide 

 of zinc, 7-18 ; and sulphide of lead, 1-66. These results differ but 

 little from the composition of specimens of polytelite from other 

 localities to which the formula 4 (Cuj, Ag, Fe, Zn, Pb) S, Sb Sg is 

 attributed ; it appears not unlikely, however, that in such metallic 

 sulpho-salts the copj^er may really be in the form Cu S. 



Polytelite from the Tjjddynglwadis Silver Lead Mine, N. Wales. — 

 This mine lies in the valley of the river Mawddach, near Dolgelly, 

 and is close to the junction of the Cambrian rocks with the Lower 

 Silurian Lingula beds, the main lode cutting through the Menevian 

 group with its associated diabases. The polytelite is disseminated 

 in the lead ores of this mine, and was with difficulty isolated in 

 sufficiently pure a condition for analysis. Its associated minerals 

 are native gold, native silver, galena, chalcopyrite, blende, iron 

 pyrite, arsenical pyrites and quartz. Assays showed the polytelite 

 to contain 11-25 per cent, of silver. In the washing of the ores of 

 this mine it had been noticed that the lighter slimes were the 

 richer in the precious metals, which the author imagined to be 

 due to the greater part of the silver occurring in the form of poly- 

 telite (specific gravity 4-8), and not as a constituent of the galena 

 (specific gravity, 7*7). He succeeded, by careful washing, in 

 separating the metallic portion of the powdered ore into two layers, 

 the lighter in which was most of the polytelite, containing 182 

 ounces of silver per ton, and the denser, consisting of argentiferous 

 galena, yielded 60 ounces of silver per ton. 



Sulphides of Iron and Nickel. — The sulphide of iron and nickel 

 from the nickel mine, near Inverary Castle, Argyllshire, possessed 

 the following characteristics : massive ; fracture between granular 

 and semicrystalline ; brittle ; opaque ; lustre metallic ; colour, light 

 bronze-brown ; hardness, 3*5 ; strongl}'- magnetic ; specific gravity, 

 4*5. It was composed of 38*01 per cent, sulphur, 50*66 iron, and 

 11*33 nickel ; and is probably to be regarded as composed of 

 Millerite and pyrrhotine. Some specimens of nickeliferous pyrrho- 

 tine from this mine are studded with brass-yellow spots resembling 

 iron pyrites, and after the lapse of some years the double sulphide 

 becomes disaggregated, whereby the separation of the yellow 

 mineral can be effected. Its specific gravity was found to be 4*93, 

 and its composition : sulj^hur 43*32, iron 45*73, nickel 1*99, cobalt 

 1*24, copper, 1-18. The iron pyrites appears to have segregated out 

 of the general mass, carrying with it the cobalt and copper, scarcely 

 a trace of cobalt being found in the pyrrhotine ; and there appears 

 to be a tendency on the part of cobalt to associate itself with bisul- 

 phide of iron, whilst nickel appears to prefer uniting itself with the 

 magnetic sulphide. A chemical examination of several hundred 



