Chap. VII.] 
UPPEE LUDLOW ROCKS. 
137 
right bank of the Wye, but in which no limestone occurs, exhibit a fine 
upward development, as they pass under the Old Red Sandstone in the 
wilds of Mynydd Epynt (see the long vignette, p. 58, and Chapter XI.). 
There the Upper Ludlow rises from beneath the Old Red, in a rapid anti- 
clinal flexure at Alt-fawr and Corn-y-fan, as here represented, the central 
Brecon Anticlinal of Ludlow Rocks, throwing off Old Red Sandstone. 
(From Sil. Syst. p. 211.) 
N.W. Alt Fawr and S.E. 
Corn-y-fan. 
e 2 e l e 2 e 3 
e\ Lower Ludlow, e 2 . Middle Ludlow, with a calcareous band representing the 
Aymestry limestone, e 3 . Upper Ludlow. /. Old Red (lowest beds). 
and lower members of the formation forming the underlying, arched, un- 
tinted strata, e 1 . 
Thence into Carmarthenshire, the junction of the Ludlow rocks with the 
Old Red Sandstone is well laid open in numerous places, especially in the 
narrow valley of Cwm Dwr, between Trecastle and Llandovery, where the 
Tilestones, on which Horeb Chapel stands, are full of the casts of Shells, 
among which are characteristic forms, such as the Platychisma helicites, 
PI. Williamsi, Bellerophon trilobatus, and many others. 
The banks of the River Sawdde, in Carmarthenshire, east of Llangadock, 
also expose a good junction of these highly micaceous Upper Silurian 
flagstones with overlying Old Red marl, the whole at very high angles 
of inclination. Thence, in its range to the mouth of the Towy, the Upper 
Ludlow becomes a compact hard sandstone, everywhere surmounted by 
Old Red*. 
In Pembrokeshire, similar junctions with the Old Red Sandstone are seen 
near Tavern Spite, Narberth, at Freshwater East and West, and in Mar- 
loes Bay. In all these places, strata of dull greenish-grey argillaceous 
sandstone, minutely micaceous, differing from the type of the Upper Ludlow 
of Shropshire in being harder and thicker-bedded, repose on rocks with 
Upper Silurian fossils, and plunge under red and green strata (the ' red 
rab ' of Pembroke), or bottom beds of the Old Red Sandstone. 
In the Valley of Woolhope, particularly in Backbury Camp, Seager Hill, 
and in the transverse gorges or hollows locally called ' Cock-shoots,' the 
same succession is very apparent all round the external rim of that remark- 
able elliptical elevation (see diagram, p. 110). In nearly all parts of that 
boundary, the Upper Ludlow is well exposed in its characteristic lithological 
condition, and is copiously charged with its prevalent fossils, Chonetes 
* See woodcuts, pp. 55, 56. 
