VOL. XIX. (z) 
THE SILURIAN INLIER OJ- USK 
133 
the Coed-y-paen anticline one passes over Ludlow rocks on 
to Wenlock beds, which all show an anticlinal arrangement to 
the south of the Berthin Brook. Beyond, however, the 
Monkswood drift obscures the Silurian beds, and when these 
beds are once more seen, near Trostrey, the anticlinal structure 
is no longer clear. To the South of the Berthin Brook the 
Ludlow beds are almost everywhere resting conformably on 
Wenlock Limestone, and this rock on Wenlock shales. To the 
North of the river Usk, however, along the Eastern margin of 
the Wenlock shales is a fault which brings Ludlow beds against 
them, and no trace of Wenlock Limestone is to be seen, while 
to the West also Ludlow beds are brought against the Wenlock 
shales by a fault which runs close to the Chain Bridge. 
The Northern limit of the Wenlock shales is entirely 
masked by the Bettws-Newydd drift. 
The Western margin of the Silurians from Clytha in the 
North to the Usk railway is entirely covered by Alluvium or 
drift, but south of the railway a fault separates the Ludlow 
and Wenlock beds from the Old Red Sandstone as far as 
Trostra Common. Along the remainder of the boundary of 
the Coed-y-paen anticline, however, the junction between 
the Ludlow beds and the Old Red Sandstone is no longer a 
faulted one, and a thin bed of yellow quartzose sandstone, 
which is the basement bed of the Old Red Sandstone in this 
region, is seen at Trostra Common, at a spot South-East of 
Panteg, near Llanthewy Court, just below Llandegveth Church 
and in the road 300 yards to the North of that Church. 
From Llandegveth Church the boundary of the Silurian 
turns North-westwards towards Graigwith House, showing 
that we have here passed round the nose of the Anticline. 
Grey quartzose grits are seen dipping South near Graigwith 
House, and the Survey records similar grits in the brook East 
of Llandegveth Church. These, no doubt, are in the base- 
ment beds of the Old Red Sandstone, and show that here, too, 
there is no fault bounding the Silurian beds. The whole of 
the Western margin of the Cocd-y-pacn anticline is a fault- 
line which runs up from Graigwith }>ast Tyn-y-cceau, Cefn 11a 
to Rhadyr, and then, passing under the Usk, is traceable 
along the base of Llancayo Hill, and, turning to the North- 
West, passes under drift near Bettws-Newydd. 
