512 
THE GEOLOGIST, 
giilas. The Cambrian rocks are coarse greenish-grey grits. The Lingula-flags 
are arenaceous slaty -beds, iuterstratified 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 
gold. 
According to Sir Roderick Murchison, " 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, teUuric 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. P. Walpole, Sir Augustus Webster, my- 
self, and others ; and Mr. Artliur Dean, in a paper read before the British 
Association in 1814, stated, " that a complete system of auriferous veins exists 
throughout the whole of the Snowdouian 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 diflicult to understand. 
About ten years later, gentlemen of my own acquaintance, after ha^g 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, althougli 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 present 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. 
