490 
The Old Red Sandstone lies, then, 
conformably upon the Silurian ; it 
likewise passes conformably be- 
neath the Carboniferous Limestone 
of the Taff Gorge; and it shows no 
signs of being unconformable to 
itself. Thus the existence of an 
ascertained base-line to the Old Red 
Sandstone near Cardiff gives us a 
fresh opportunity for determining 
the thickness of this formation. 
Good exposures, however, of the 
Old Red Sandstone are rare, and 
over a wide east and west valley 
south of Lanishen almost entirely 
wanting. Still certain points of 
importance can be made out, the 
best section to follow being that of 
the Rhymney railway, which, from 
the Starting House on Heathtarm 
Hill to the Carboniferous escarp- 
ment, cuts directly across the strike 
of the intermediate Silurian and 
Old Red Sandstone beds. The 
section is given here (fig. 5). 
On the railway, just south of the 
Starting House, an anticlinal is 
seen bringing up the Rhymney 
Grit and Wenlock beds. The axis 
of the anticlinal strikes nearly due 
east and west; and the beds on its 
north side dip at an angle first of 
25° and afterwards of 45° towards 
the north. The railway is then 
carried along an embankment, and 
affords no insight into the nature 
of the country for a mile after 
leaving the Silurians. Running 
parallel with the railway, how- 
ever, we haye on the other side of 
Nant-mawr the range of hills 
which stretch from Pen-y-lan 
northwards; and this supplies us, 
for the southern half of the inter- 
val on the railway, with sections 
in which the Old Red Sandstone 
is exposed, with a persistent dip 
more or less to the north. 
The wide east-to-west valley which 
rendered the railway embank- 
"JOABL) *"D 
"goTBYG snOLofIUOgILD “9 
‘OUOJSPULY poy PIO ‘2 
“UBLINTIQ “p 
W. J. SOLLAS ON THE STLURIAN DISTRICT 
o 
"wasng-jn0g YsjaM ayy fo 
‘wily Ymary ‘osnopy hurpungy ayr woul ‘hnayuny howulhyay ayy Huopp worjoagy—'G ‘Si 
Workman’s ex- 
cayation. 
Bridge and Sta- 
— 
tionto Lanishen [4 
(dip7°froms.W. ©& 
to N.E.) de 
Bridge. = 
5 miles. 2 
mn 
oO 
3 
oe 
25 
fe) 
3 “ = 
Signal-box (dip + 
reese 11° from N. to 
8.). wie 
ERS 
ors Bridge ie 
THM Sh 
aS 
Ss] 
hse, Bridge = 
oS 
Ss 
° Ss 
S 
S 
e 
------- 6 miles. = 
ae Tunnel. SS 
& 
aw 
—--- Shaft. = 
= 
-- Quarries. & 
= 
~ 
64 miles. 
