THE VALE OF CLWYD. - 15 
fault, and the boundary line creeps away up the hill towards 
Penybyrn. Along the smashed rock near the fault in the 
weathered surface of the Silurian, and perhaps also in the sandy 
beds of the Carboniferous basement series, there have been 
mining trials. A section exposed just above the shaft showed 
8 inches of limestone resting on 18 inches of red and grey shale. 
In the débris there were traces of copper and some iron pyrites. 
Fic. 6. 
Section seen between Buarthau and Felin Meredith, near Rhewl. 
(Scale, 40 feet to 1 inch.) 
a. Gravel ; probably old river terrace. 
6. Mountain Limestone. 
c. Basement Bed of Carboniferous (= part of Devonian or Upper Old 
Red); consisting of beds of Sandstone, 6 to 8 inches thick, in 
red, grey, and green shale. 
f. Fault. 
Fic. 7. 
Section seen in bank of river near Felin Meredith, Rhewl. 
: (Scale, 5 feet to 1 inch.) 
a. Gravel; old river terrace. 
6. Basement Bed of Carboniferous (= part of Devonian or Upper Old 
Red.) : 
c. Silurian Flags, upon the upturned and jagged edges of which the 
Devonian lies. 
Fic. 8. 
Section seen in stream below cottage S.W. of Lianfwrog, Ruthin. 
a. Devonian or Basement Bed of Carboniferous; no conglomerate seen 
at base. 
6. Silurian. Flaggy shales ; top stained like the ‘*‘ Moughton Whet- 
stones.” 
a tt el ie ee ae 
THE MountTAIN LIMESTONE. 
The Mountain Limestone is, I think, capable of subdivision, 
in some parts of the district at any rate. 
There are many beds of peculiar character which help one to 
trace certain horizons for short distances, and which may some 
day prove of considerable classificatory value when the zones of 
_ life also have been worked out. Some of these beds are of 
economic value—the bands of thin-bedded limestone in the 
Tyddyn Uchaf Quarries, near Denbigh, for instance, which 
_ naturally split up into blocks of convenient thickness for build- 
_ing purposes ; and the even bedded, sometimes oolitic limestone 
of the Henllan Quarry—where there are also some curious 
layers of fine buff soapy clay, and bands of a lithographic 
stone. In the quarry at Penisaf-y-glasgoed, near Bodelwyddan, 
there is along one side of the quarry a bed, about z feet thick, 
of grey, yellow, and rusty clay, belonging to the Mountain 
