A, R. Andrew—The Dolgeliey Gold-belt. 267 
by glacial drift; to the west it lies in the Vigra Beds, and towards 
the east in the Pen Rhos Beds. Very little greenstone is to be seen 
along the course of the vein. The levels by which the lode was 
opened have now fallen in; where the lode outcrops, the quartz is 
white and opaque, with very little mineral. Specimens from this 
lode are to be seen in the Museum of Practical Geology, Jermyn 
Street, and of these Maclaren has said (38, p. 453): ‘‘The invariable 
associate. of the gold is zinc-blende, the latter being sometimes con- 
temporaneous and sometimes prior in point of deposition; galena and 
pyrites also occur, and indeed the veins were originally worked as 
a silver-lead mine.” The total reported output of this mine from 
1860 to 1905 has been 123 ounces of gold from 50 tons of quartz. It is 
stated also that in the early days this mine gave two large returns, 
ageregating 318 ounces of gold from 4574 tons of stone, but there 
are no figures to support this statement. 
Gwyn-fynydd Lode.—On the southern flanks of the Moel Gwyn- 
fynydd, about half a mile north of the junction of the Afon Gain and 
the Mawddach, several disused levels and shafts mark the outcrop of 
the Gwyn-fynydd lode. Like the majority of the lodes of this district, 
it is found along with parallel companion lodes, as many as twenty of 
these having been passed through in the cross-cut which opens up the 
mine; one of these companion lodes is in places 20 feet thick, and is 
known as the Chidlaw lode. The strike of the Gwyn-fynydd vein is 
about 70° east of north, and the dip is towards the north, never flatter 
than 70°. The outcrop can be traced for a distance of about 14 miles; 
at its western end it cuts across the top of the Barmouth Grits, then 
through the whole of the Gamlan into the Clogau Beds. Here the out- 
crop is thrown to the south by the Afon Gain fault, which courses down 
from the north. The lode then continues through the Clogau Beds 
into the Vigra Beds, in which it terminates against the Gwyn-fynydd 
fault, on the eastern side of which it has not been picked up. The 
lode in its course cuts through sills of greenstone, but these are not 
numerous. The thickness of the lode is variable: in the parts where 
it has been worked (i.e. in the Clogau Beds) it is from 3 to 25 feet in 
width, to the west and to the east it may often be as thin as 2 or 8 feet. 
Often the lode includes large bodies of slate and shale. The lode 
material consists of very white quartz, with great patches of galena, 
pyrites, and chalcopyrite in finely granular aggregates. In addition 
to the above, orpiment, pyromorphite, and mimetite (40, p. 693), 
arsenopyrite and blende (38, p. 452) are said to occur. Gold has 
only been found at those places where the vein crosses the Clogau 
black beds. Where it occurs it is often in a very finely divided 
state ; sometimes, however, it is massive and arranged as in irregular 
veinlets. During the period 1864-1907 this mine has produced 
36,116 ounces of gold from 96,569 tons of stone; during certain 
periods (especially 1888-92) it has furnished practically all the gold 
output of Merionethshire. 
SUMMARY OF THE AvnriFerous VEINS. 
It is to be remarked that in the Dolgelley Gold-belt not a single 
auriferous vein is found in any formation lower than the Clogau 
