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

10 CAHBOXIFETCOUS BOCKS.
The pit has been opened in soft red and white sandstone (New
Red Sandstone), but towards the west touches a breccia made o£
fragments of Basement Beds and New Red Sandstone mixed,
and containing specks of copper-pyrites. On. digging through this
breccia, which is clearly " fault-stuff," we quickly reach the Basement
Beds in place. Towards the south this fault throws limestone
and Basement Beds in succession against Wenlock Shale ; the
Basement Beds, however, are not well exposed for nearly half a
mile, though they run on as far at least as Efenechtyd (Quartersheet
74 N.E.), where a shaft has been sunk into white and
yellow sandstone belonging to this subdivision. Another fine
exposure of these strata occurs in the valley: of the Clywedog, just
beyond the margin of this map (see also p. 15).
(2.) The Carboniferous Limestone, Millstone Grit, and Coal-
Measures.
Commencing with the eastern side pf the Vale, and working
southwards, we meet the first exposures of limestone at
Pen-llwyn and Fron-yw. A quarry near the former exposes
limestone, stained red, shattered, traversed by strong curving and
slickensided joints, and dipping towards the south-west and west at
45°. The breadth of outcrop cannot exceed 250 yards, for Silurian
rocks occur immediately east of the quarry, while in the wood
below a strong ppring marks the junction of the limestone andsNew
Red Sandstone. Whether the red sand here rests naturally on the
limestone, or is thrown against it by a fault, remains doubtful. No
conglomerate or breccia occurs, as might have been expected in
the former case, but on the other hand red^-staining is a common
feature in rocks on which Trias has been deposited. In the limestone
to the north of the quarry the red colour has led to some
explorations for haematite. The next exposure southwards occurs
in a small hole, 100 yards west of Fron-yw, where limestone seems
to dip westwards at 45°, but the bedding-planes are obscure.
About Plas-Llangwyfam the rock is concealed by Drift, but
comes into view again in the stream at Rhiw-pebyll, where a quarry
shows shattered limestone. Some coal, said to have occurred in
this quarry, seems to indicate that the beds belong to the lower
more probably than to the upper limestone (p. 19), but they are
nevertheless faulted against the Wenlock Shale, as may be seen in
the brook. The shale is completely smashed up near the line of
junction.
The limestone again appears behind the farmhouses, 300 yards
further south, where it is intensely shattered, and abundantly
infiltrated with sulphate of baryta. It seems to occur as a wedge
in a split of the Vale of Clwyd Fault, being thrown on the east
against Wenlock Shale, or rather a blue clay formed by the complete
trituration of this rock, and on the west against red rocks,
proved in an old shaft and borehole by the side of the road, but
•whether stained Goal-Measures or Trias could not be ascertained.
An old quarry 250 yards east of Groes-fawr, by the stream to
Gales, furnishes the next exposure. There again the limestone is