' VOL. XIX. (2) 
THE SILURIAN INLIER OE USK 
149 
railway-cutting, however, suggests the presence of Old Red 
Sandstone there. From these exposures were collected : — 
Lingula sp. 
Styopheodonta sp. 
Leptcena rhomboidalis. 
Chonetes striatella. 
Oytkis limata. 
’> poly gy amnia. 
1 1 ' ilson ia Davidsoni. 
Camayotcechia nucula. 
Dayia navicula. 
Spiyifey cyispiis. 
Whitpeldella didynia. 
Ptei'inea naviformis. 
,, cf. subfalcata 
var. 
Ctenodonta .sp. 
Modiolopsis sp. 
PalcBOpecten Danbyi. 
Gyammysia sp. 
Oythonota amygdalina. 
,, sp. 
Bellerophon all. lale- 
vittatns. 
Orthoceyas sp. 
Calymene intey media. 
Phacops Downingice. 
The top of the ridge running Northwards from Usk Castle 
is drift-covered, and no more exposures are seen till one comes 
to Cwm Cayo. On the top of the ridge here hard red sand- 
stones of the Old Red Sandstone series are seen dipping 15° S.E., 
while in the stream below are Ludlow sandstones dipping 20° 
S.S.W., and lower down at 5° \V. Here, therefore, as in the 
Llangibby district, the Eastern margin of the Silurian Inlier is 
a line of fault. 
In the lofty cliff by the road, just to the North of where 
the Cwm Cayo Brook enters the Usk, the Ludlow sandstones 
dip 20° N. This Northerly dip is, no doubt, due to a fault 
which crosses Cwm Cayo just below Baldwin’s Farm, and 
throws back the Eastern margin of the Ludlow beds about 
300 yards to the East. 
From the fossil evidence and from the character of the 
beds in this portion of the Inlier we may class them with the 
lower division of the Ludlow beds of the Coed-y-paen Anti- 
cline. 
IV. {b). THE EXPOSURES BETWEEN CWM CAYO 
AND LLANCAYO HILL CAMP. 
On the North side of the Cwm Cayo fault Ludlow beds are 
seen by the Usk, and dip 20° E. They are hard greenisli sand- 
stones, with occasional calcareous bands and nodules. 
Near Baldwin’s Farm are two (piarrics, which show sand- 
stone and impure limestone, wliilc in the stream above the 
farm, dipping at first 10° E., and then, as the marginal fault 
is approached, 55° JC, are more Ludlow sandstones, with 
