The geology of the neighbourhoods of Flint, Mold, and Ruthin ...

6 UPPER SII/UKTAN ROCKS.
westerly bend in the beds north of the fault indicated on the map,
there are some trials in a quartz-vein, bearing about E. 37° S.,
and said to contain specks of copper. There, as elsewnere in
these rocks, vein-quartz occurs, "whether in a vein or joint, only in
or close by beds of sandstone, from which the silica may consequently
be presumed to have been derived. Another trial for copper has
been made in a crag of shattered sandstone full of strings of
quartz about a mile west of the tower on Moel Fammau. There
appears to be an ill-defined vein running about north-east, also
reported to contain specks of copper.
South of the fault shown, the sandstone dips down the slope at
a gentle angle south-westwards, and consequently covers a broad
spread. It may be traced thence round the northern and eastern
sides of Moel Fammau through some old quarries, being seen in
one place to exceed 12 feet in thickness and to contain small
encrinites and clay-galls.
The outlying hill of Moel-y-Gaer* consists of contorted shales
with lumps of sandstone. On the eastern and north-eastern sides
of the hill some slate-quarries have been opened upon an anticline,
the cleavage ranging about E. 1 0° S., or locally E. 1 0° N.
Four hundred yards south of this hill a quarry in the
bottom of the valley exposes flags with Orthoceras primavum and
Cardiola interrupta. Several parallel ridges formed by the outcrop
of bands of sandstone are passed on the way up Moel
Fammau from Bwlch-pen-barras. The beds dip to the north and
north-east so as to sweep round the west side of the hill, but
cannot be traced more than two or three hundred yards. On the
Bwlch there occur shales with concretions and in places flaggy,
dipping south and south-westwards. The same dip prevails on
Foel-fenlli in shales with thin sandstones, exposed about the east
end of the camp.
Where the Mold and Ruthin road crosses the range (at a
height of 944 feet above the sea), a south-westerly or southerly
dip prevails in sandy or occasionally flaggy shales ; still further
south along the watershed the dip becomes locally south-east, in
shale with thin sandstone, but further to the west resumes the
prevalent westerly to south-westerly direction. In the next
Quarter-sheet a southerly and south-easterly dip prevails.
The Silurian rocks occupying the southwestern corner of the
map belong to the same subdivision, and call for no particular
notice. -A general description of the Upper Silurian strata of
Denbighshire will be found in the Geology of North Wales
(Geological Survey Memoirs, vol. iii.), by Sir A. Ramsay, and in
Notes on the Geology of the Vale of Clwyd (Proc. Chester Soc.
Nat. Sci. No. 3, 1885), by Prof. T. McK. Hughes.
JTot to be confounded with Moel-y-Gaer on Halkin Mountain.