264 A. R. Andrew—The Dolgelley Gold-belt. 
Gwyn-fynydd lodes, this is the most important lode in the Dolgelley 
belt. On the slopes of Cefn Coch Hill, and to the north-east, it strikes 
45° east of north; to the south-west the strike becomes more northerly 
(25° east of north) for about half a mile; then on the slopes of Foel-ddu 
the lode regains its original strike; the total traceable outcrop 
amounts to about 2 miles. : 
Through the greater part of its length, the lode runs along the 
contact of the Clogau Slates and the Gamlan Shales. The topmost 
bed of the Gamlan group is here a coarse-grained quartzose grit, and 
at times the lode is represented by a series of stringers ramifying 
through this grit. Westward over the shoulder of the Cefn Coch 
Hill, the lode lies mostly in the Gamlan green shales and grits. 
Greenstone sills occur at intervals along the course of the lode and 
form one or both walls. This lode has been cited by earlier writers, 
e.g. Ramsay (12-15), as an instance of a vein forming the continuation 
of a greenstone dyke, but I have not been able to see anything more 
unusual than the pinching out of the lode close to a greenstone sill, 
The Cefn Coch lode branches frequently and is accompanied by 
parallel veins. The dip of the lode is towards the north-west, so that 
it very soon becomes confined to the Gamlan Beds below the surface. 
Its width varies from 6 inches up to 3 or 4 feet, occasionally swelling 
out into massive blebs of quartz, 10 to 12 feet thick. No clay 
selvage is present in the lode. 
The quartz of the lode is not well mineralized, though the parts 
already worked out probably contained a much larger proportion of 
mineral than those now exposed. The most usual minerals in the 
quartz are blende and galena, and there are also chalcopyrite, pyrites, 
zincite, and gold. An analysis of the gold from this lode gaye the 
following result: gold, 76°40 per cent.; silver, 22°70 per cent. 
Between the years 1863 and 1908, though the work has been of 
a most intermittent character, 2310 tons of quartz have produced 
1193 ounces of gold. 
Cae-mawr Lode.—This lode is seen on the hills on the western 
bank of the Mawddach near its confluence with the Afon-wen. The 
lode has little extent in strike; it strikes 15° south of east, and dips 
to the south at an inclination of 40° to the vertical. It intersects the 
Pen Rhos Beds of the Maentwrog, where its walls are clearly defined ; 
the lode is wide, from 8 to 15 feet across. The metallic mineral 
contained in the quartz of the lode is of small amount and consists of 
chalcopyrite alone. In 1891 development work on this lode produced 
10 tons of quartz for a return of 1 ounce of gold. 
Dol-y-clochydd Lode.—Opposite the Precipice Walk, on the crags that 
overhang the Dolgelley-Trawsfynydd road, outcrops of white quartz 
have been opened up by a cross-cut. The lode can be traced 
satisfactorily only for the extent of the greenstone sill in which the 
cross-cut is driven, but a few isolated outcrops probably mark 
a continuation along the line of lode beyond the sill. The quartz of 
the lode contains some chalcopyrite; its strike is 45° east of north. 
The lode and its accompanying greenstone sill lie among the Pen Rhos 
Beds, while the isolated quartz outcrops range up into the lower part 
of the Ffestiniog group. 
