56 
SILUKIA. 
[Chap. III. 
deilo and in Dynevor Park, and containing, together with Asaphus tyrannus, 
the following :— Calymene brevicapitata, Trinucleus Lloydii, Leptaena sericea, 
Orthis calligramma, &c. 
An arched arrangement of the strata is also traceable to Llangadock, 
where a dome of grits and sandstone, like those of Pont Ladies, emerges 
from beneath the superior strata, as represented in this diagram. 
Section near Llangadock. From the Lower Silurian to the Old Eed Sandstone. 
(The spectator is looking to the south-west.) 
f e d b' b * b * b b 
b. Undulations of Llandeilo schists, flags, and limestone, with interstratified trap *. 
b'. Llandeilo sandstones, &c. d, e. Upper Silurian. /. Old Eed Sandstone. 
Of like age also are the grits and pebbly beds of Mount Pleasant and 
other places opposite Carmarthen, from which the fossils Orthis alata, 
Bellerophon perturbatus, Ctenodonta? lsevis, and Stygina Murchisonias 
were obtained during my early labours (1833-4 X)> 
Whilst such are the chief features of the Llandeilo rocks in Carmarthen- 
shire, it is essential to remark that certain sandy beds on the left bank of 
the Towy (&'), ranging by Cairn-goch, which were formerly considered to 
be Caradoc Sandstone (see Sil. Syst. p. 354), are now known by their im- 
bedded remains to belong to the Llandeilo formation. Along this frontier 
therefore, notwithstanding an apparent conformity (for the old sections 
published in the ' Silurian System ' scarcely differ from those of the Govern- 
ment Surveyors), there is a great hiatus, as determined by the subsequent 
labours of Ramsay, Aveline, and Salter. There, on the left bank of the 
Towy, the true Caradoc group (c) is omitted, and the Upper Silurian rocks, 
with a feeble trace of a sandy rock containing Pentamerus oblongus, at 
once overlap the Llandeilo formation. This arrangement, by which the 
Caradoc formation is excluded, extends all along the left bank of the Towy 
from the environs of Carmarthen, by Llandeilo, and is prolonged far to the 
north-east. 
On the other hand, a natural exhibition of the Caradoc rocks is seen on 
the opposite bank of the river, where an unbroken ascending series is ex- 
hibited, in which both the Llandeilo and Caradoc formations are exposed 
in conformable apposition. To the north of Llandeilo, the calcareous Tri- 
lobite-flags, folding over to the N.N.W., are at once surmounted by a great 
t Cairn-goch is a remarkable and rather large British fort, in which the defenders have availed 
themselves of the smooth faces of a steep anticlinal of these grits, as walls of defence, the ends of the 
entrenchment being blocked up by loose fragments of the stone. 
J See Sil. Syst. p. 358, and pi. 25. 
