512 



THE GEOLOGIST. 



gulas. The Cambrian rocks are coarse greenish-grey grits. The Lingula-fiags 

 are arenaceous slaty-beds, interstratified with courses of sandstone. Calcareous 

 and greenstone dykes frequently penetrate both the Cambrian and Silurian 

 rocks. In the latter, the direction of the dykes is generally parallel with the 

 lines of bedding ; in the former, if any particular order obtains, their general 

 direction is rather across the strike. 



The metalliferous products are chiefly galena, copper pyrites, blende, man- 

 ganese, and mundic, most of which are frequently found associated with native 



According to Sir Roderick Murchison, 6C The most useful position of gold is 

 in quartzose veinstones, that traverse altered palaeozoic slates, frequently near 

 their junction with eruptive rocks, whether of igneous or of aqueous origin. 

 The stratified rocks of the highest antiquity, such as the oldest gneiss, or 

 quartz rocks, have seldom borne gold; but the sedimentary accumulations 

 which followed, or the Silurian, Devonian, and Carboniferous (particularly the 

 first of these three) have been the deposits, which, in the tracts where they 

 have undergone a metamorphosis or change of structure, by the influence of 

 igneous agency, or other causes, have been the chief sources whence gold has 

 been derived." — Siluria. 



Referring to the discoveries of gold in the Dolgelly district, Professor 

 Ramsay says : "In the Ural Mountains, South Australia, Canada, and other 

 parts of the world, gold occurs in rocks of the same general age, and appa- 

 rently under the same circumstances." — (" Geologist," Feb., 1858.) 



Sir R. Murchison's statement is singularly corroborated by the position of 

 the quartzose vein in the Clogau mine, distinguished as the " gold lode," 

 which traverses altered palaeozoic slates, near the junction of an eruptive bar 

 of porphyritic greenstone, and the same law appears to obtain, also, with 

 respect to all the gold-bearing quartzose veins of the Dolgelly district, upon 

 the ores of which the author has made a very large number of experiments 

 during the past eight years. 



There are, in this district, about twenty localities in which gold has been 

 discovered, visible, in quartz, or associated, more or less, with galena, blende, 

 copper-pyrites, telluric mismuth, carbonate of lime, schist, baryta, iron- 

 pyrites, &c. 



By far the richest discoveries of gold have been made at the Dol-y-frwynog, 

 Prince of Wales, Cambrian, and the Clogau Mines. Gold has also been found 

 in the " Marine Drift," by the Hon. F. Walpole, Sir Augustus Webster, my- 

 self, and others ; and Mr. Arthur Dean, in a paper read before the British 

 Association in 1844, stated, " that a complete system of auriferous veins exists 

 throughout the whole of the Snowdonian or Lower Silurian formations of North 

 Wales." 



Upon faith in this statement much current gold of the realm was expended 

 at the Cwmheisian Mines, and very little bullion obtained by smelting oper- 

 ations, for reasons which are now not very difficult to understand. 



About ten years later, gentlemen of my own acquaintance, after having set 

 the most eminent assayers to work, to prove the accuracy of Mr. Dean's state- 

 ment, expended nearly as much money upon the same spot, in the erection of 

 machinery, which produced even less gold by amalgamation than the former 

 method, although it was then held as an axiom that gold always exists in a 

 metallic state, that mercury always has an affinity for gold, and, therefore, 

 whenever gold is preseut in minerals, mercury will necessarily dissolve it. 

 This did not, however, prove to be the case. 



The result of operations upon some hundred and fifty tons came at length 

 to be considered, at the best, an inigmatical failure, as the following extract 

 from notes of the experiment will show. 



