56 REPORT — 1844. 



the rock escaping conversion on the diminution of the temperature. On three sides 

 of the quarry the variegated sandstone was observed resting on the trap without having 

 been dislocated or deranged by it, and this also appeared to Mr. Williams only to be 

 explained by supposing tranquil fusion and conversion. " If the amygdaloid," he said, 

 " had in either case been forcibly protruded, it must have displaced very many millions 

 of cubic yards of sandstone and caused great derangement; yet there was not a particle 

 of evidence of anything of the kind having taken place." The author concluded by 

 stating that he had discovered instances of the process of fusion and conversion in all 

 the slates, sandstones and limestones of South Devon and Cornwall, in the mountain 

 limestone of the Mendips, and the variegated sandstones about Exeter, all of them ex- 

 plicitly and emphatically negativing the hypothesis of injection. 



Notice respecting the Discovery of Gold Ores in Merionethshire, North Wales. 

 By Arthur Dean, C.E. 



The author stated, that in 1843 he discovered some rich gold ores at the Cwmhei- 

 sian mines near Dolgelly. Further researches proved that a complete system of 

 auriferous veins exists throughout the whole of the Snowdonian or lower Silurian 

 formations of North Wales. 



The structure of this district is very singular, consisting of an immense number of 

 alternate and parallel beds of igneous and sedimentary rocks, traversed by vast num- 

 bers of mineral veins and trap dykes. 



These mineral veins are of three periods of formation ; those of the first period have 

 an average bearing from S.E. to N.W., with a dip to the north ; they contain quartz 

 impregnated with ores of argentiferous galena, copper, iron, and blende, &c. The 

 veins of the second period have a general bearing N.E. and S.W., with a northern 

 dip, and contain carbonates and sulphates of barytes and lime, galena, blende, &c. 



The third set, comprising the auriferous veins, traverse both the other two, and have 

 an average bearing of N.N.E. and S.S.W., and like the others, with a north dip. These 

 veins are very numerous, and are filled with argillaceous substances, iron pyrites, and 

 iron and blende ores. In width they vary from \i\x of an inch to 6 or 8 inches, but 

 sometimes expand to 2 or 3 yards. In many cases they split into a great number of 

 minute branches. Where the auriferous veins traverse quartzose veins of the first 

 series they are generally very productive of gold, the quartzose veins, if metalliferous, 

 becoming enriched on the south side of the intersection. The sides of the auriferous 

 veins, where they pass through quartzose veins, are generally cellular, and in these 

 cells the gold, in a fibrous form, is for the most part deposited, accompanied by various 

 ores of iron, blende, galena, &c. 



In almost all cases in this district, where the mineral veins intersect each other, the 

 intersected vein, if enriched at the junction, is productive only on the south side of 

 the intersection, while it dips towards the north ; and the intersecting vein, if also en- 

 riched, carries its ore from the point of intersection towards the north. Veins dipping 

 south are almost always poor. 



If a vein runs east and west, and the strike of the strata be north and south, the 

 courses of ore follow the dip of the strata most favourable to their production. 



Some of the gold ores discovered produce from 3 dwts. to 60 ounces of gold per ton 

 of ore as broken ; and some of the washed sulphurets of lead contain lead, 75 per cent; 

 silver, 40 ounces ; gold, from 2 to 20 ounces per ton. 



Observations on the Stratification of Igneous and Sedimentary Rocks of the 

 Loioer Silurian Formation in North Wales. By Arthur Dean, CE. 

 In this communication the author stated his opinion that the igneous and sedimen- 

 tary rocks of North Wales were for the most part of contemporaneous origin, the ig- 

 neous rocks being regularly interstratified with the others, and not presenting any 

 appearance of having been subsequently injected between the strata. Sometimes at 

 least fifty alternations of parallel beds of igneous and sedimentary rocks may be found 

 within the distance of a mile, varying respectively from one foot to sixty y.irds in 

 thickness. In many cases also several beds of igneous rocks rest upon one another 

 •without the intervention of sedimentary rocks, such beds occasionally thinning out 

 and disappearing. 



