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

22 .
CARBONIFEROX'S BOOKS.
About G^meddwen andGorsa bed of fine white limestone of
saccharoid texture occurs ; in the former place it runs under the
more northerly of two limekilns and is about eight feet thick.
On crossing this presumable line of fault, we find the beds
after several minor undulations assuming a northerly and easterly
dip so as to pass naturally under the upper Black Limestone of
Pen-y-ball, near Holywell, and of Halkin Mountain respectively.
South of Calcoed Hall we meet with grey and white massive
limestone, with a northerly dip, which, towards the north, is
,
succeeded by grey beds with chert-bands and a white bed with
abundant Productus giganteus, , seen near
southern edge of the Common a row of
Calcoed. Near the
pits displays a black
hydraulic limestone closely resembling the Black Limestone
(" Aherdo " Limestone) of Holloway. The beds dip to the northeast
at 8° to 10°, so as to appear to pass under some grey limestones
which rise to the surface at two or three hundred yards
distance, but whether they do so, or whether the Black Limestone
of the Holloway and Pen-y-ball quarries are thrown down here
by a fault, cannot be stated wi.th certainty from the prevalence of
Drift. Perhaps they more probably form a lenticular mass of
black limestones appearing locally at a lower horizon than the
Black Limestone.
The Black Limestone crops out on the north-eastern side of the
Common, along the level ground which underlies the ridge known
as Pen-y-ball Top (Fig. 3). This ridge consists of a hard thickbedded
white limestone of great purity, dipping, as does the
Black Limestone, to the north-east, This apparently anomalous
position (by which the Black Limestone appears to dip under
the white limestone of Pen-j -ball) is caused by the great Milwr
Tein, a powerful fault running along the foot of this ridge, and
throwing down the Black Limestone on the south-west. The
ridge of white limestone runs from Pant Wacco by Pantasa to
Pen-y-bryn, forming the "hading" of the Milwr vein all the
way. The stone is worked in several places, large quantities
being brought down by a tramway from Crecas to Greenfield for
exportation and for use in chemical works.