560 British Association Reports. 
of general import throughout the whole of Wales, if not much 
further. 
In fact, this N. and S. set of faults, which no one seems yet to have 
noticed, is of chief importance in the whole of this mining district, 
cutting off the veins by repeated notches and slips, and in some cases 
dislocating them widely—e.g. Gwynfynydd. As soon as the ex- 
istence and symmetry of these four lines of fault had been made out, 
the author’s task became easy ; the outlines of the country, at first 
so puzzling, leading one to them (on the rocky and uncovered hill 
sides) with great precision. 
The North and South faults certainly bear copper, and have 
been worked at Dolfrwynog for that purpose, and also on the Brynian 
Glo, further west on the Trawsfynydd Road. 
The NW. and SE. faults were only traced in the narrow dis- 
trict above described. ‘They are known to bear silver-lead, and gold 
in small quantities ; and are next in point of age. 
Then come the great strike-faults with their numerous paral- 
lel smaller faults, and cross-notches where they intersect the previous 
faults. These are not yet worked for metals. 
The NE. and E. faults preceded these, and to all appearance 
the true E. and W. ones were earliest of all. ‘These two are indeed 
the prolific veins for gold, and they have direct reference to the 
original elevation and ridging of the country. As they received 
their infilling of metalliferous deposits before the three subsequent, 
or at all events two of the subsequent systems of faults occurred, and 
are certainly the oldest set of fissures in the district, it is fair to infer 
that gold is one of the oldest minerals in Wales. 
It is, of course, for the mining proprietors of the district to ascer- 
tain accurately what metals occur in each of these systems of veins, 
and by much further and closer search to carry out, complete, and 
correct the outline. The subject is of economic importance. It is 
well known that in Cornwall the mines of tin and copper run east 
and west in accordance with the strike of the rocks, while the lead 
veins cross these aud run more in a N. and S: direction ; and, again, 
that the tin veins are repeatedly crossed and shifted by copper lodes 
ot a subsequent date; while both series have been again and again 
shifted by subsequent faults—as many as eight distinct systems of 
faults having been found in Cornwall and also in Germany, accord- 
ing to Sir Charles Lyell’s latest account in his manual. 
I have as yet only been able to make out four or five in the district 
in question, of which undoubteely the north and south lines are the 
newest. 
That the relative ages of the various infillings of the metals may 
be ascertained by such research there is little doubt. But it must 
always be remembered that if lodes be faults, as they are, the second 
movement will often open the joints of the. first, as along lines of 
greatest weakness ; and hence there will be a mixture of metals in 
the older lodes which we need not expect in the newer. According- 
ly, in the Dolgelly gold-lodes we find a mixture of Gold, Blende, 
Silver-lead, Iron, Arsenic, Copper, Sulphur, &c. And where cross- 
courses intersect the lodes, we may expect the more recent metal to 
