Researches in British Mineralogy, 225 



gold and other metallic minerals are commonly found adhering to 

 or crystallizing on their under surfaces, which may have arrested 

 these minerals in the act of being carried into lode-fissure from 

 below with the stream of liquid quartz. The specific gravity of one 

 specimen of gold was found to be 17-26, and two analyses showed 

 the per-centage composition of gold 90, silver 9*25, the remainder 

 being quartz. These numbers closely agree with the formula Aug 

 Ag. Another alloy, lighter in colour and probably richer in silver, 

 is sometimes met with in the lode. 



Stream Gold from the Biver Mcmddach. — A specimen of the dust 

 washed from the bed of the river near Gwynfyndd, some eight miles 

 from Dolgelly, contained small, flattened, elongated spangles of gold, 

 the largest having the size of a pin's head, accompanied by abund- 

 ance of fine black sand, supposed to be magnetite, but found to be 

 titanoferrite, together with some small particles of quartz, slate- 

 rock, mica, iron pyrites, and galena. The gold was found to have 

 a specific gravity of 15.79, and the following composition : gold 

 84-89, silver 13-99, iron 0.34, and quartz 0-43. Several spangles 

 had a peculiarly rich yellow colour due to a thin film of sesquioxide 

 of iron adhering to their surface. 



Titanoferrite. — The basaltic or doloritic rocks of the South Staf- 

 fordshire coal-field invariably contain a small amount of a heavy 

 black metallic mineral, strongly attracted by the magnet, and 

 generally regarded as magnetic oxide of iron, whilst analysis showed 

 it to be titanoferrite. Removed from the pulverised rock by means 

 of a magnet, it was found, on examination, tc have a specific gravity 

 of 4'69, and a composition closely approximating to the formula 

 Fcj O3 Ti O2. The associated minerals, distinguishable only in thin 

 sections when viewed under the microscope, are a triclinic soda-lime 

 felspar, augite, and a small quantity of what is probably seladonite, 

 whilst pyrites, apatite, and a zeolitic mineral are likewise occa- 

 sionally present. An examination of specimens of these basaltic 

 rocks from each eruptive boss in Staffordshire, as well as others 

 from the intrusive masses occurring in coal - pits, showed that 

 titanoferrite is invariably present, and is consequently an essential 

 constituent of the rock itself. It is, moreover, that variety of 

 titanoferrite, which usually accompanies the eruptive rocks of 

 Palasozoic age. The presence of titanium not only serves to charac- 

 terise the basalts of this district, but likewise affords a means of 

 detecting these rocks where altered by metamorphic action, and of 

 referring tuffs, clays, etc., formed from them, to the original source. 

 Two instances furnishing proofs of this are mentioned. 



Polytelite from the Foxdale Silver Lead Mine, Isle of Man. — This 

 mineral has been found in quantity sufficient to make it an object of 

 commercial consideration. The lode wherein it occurs cuts through 

 both the Lower Silurian and the eruptive granite ; the latter 

 appeared subsequent to the deposition to these beds, and is identical 

 in its mineralogical character with the auriferous granites of other 

 parts of the globe. The minerals associated with the polytelite are 

 galena, chalcopyrite, iron pyrites, zincblende, quartz, dolomite, 



