Chap. III.] 
SECTION NEAR LLAJSTDEILO. 
55 
age. When the limestone thins out, its position is in some parts marked 
Ivy lines of calcareous concretions, in other places by fossils only. At and 
near the town of Llandeilo, the chief member of the formation consists of 
calcareous flagstones, in part true limestones, which abound with the 
above-mentioned characteristic fossils. Extending northwards to Llan- 
gadock and southwards to Carmarthen, the Llandeilo flagstones rise in the 
form of a broken, elliptical mass from beneath overlying strata on both 
banks of the Towy, thus marking an extensive line of excavation in which 
that river flows. 
The preceding sketch conveys a general idea of the outline of the country, 
in which most of the Silurian rocks, from the Llandeilo in the foreground 
to the overlying formations, are exhibited. The calcareous flagstones are 
seen here on both banks of the river, and the overlying formations in the 
distance. The foreground is the undulating park of Lord Dynevor, and 
the chief mansion beyond the valley is Golden Grove, one of the seats of 
Earl Cawdor. The distant hills are composed of Old Red Sandstone and 
the lower members of the Carboniferous System. 
This succession will be better understood by inspecting the annexed 
diagram, taken from one of the large sections made by the Government 
Surveyors, which is quite in accordance with my oldest published sections 
across the same tract. 
Section near Llandeilo. From the Lower Silurian to the edge op the great 
South- Welsh Coal-field. 
(In this diagram the spectator is supposed to be placed a little south of Llandeilo, 
looking north-east, or up the Yale of the Towy. Hence the points of the compass are 
reversed in reference to the following diagram, p. 56.) 
n.w. ^ ^iis^^ 
b b b' d e f g h 
b. Llandeilo flags and limestone, b'. Llandeilo sandstone, &c. d, e. Upper Silurian 
rocks. /. Old Red Sandstone, g. Carboniferous Limestone, h. Millstone-grit. 
Subsequently, however, the construction of a railroad from Llanelly by 
Llandeilo to Llandovery laid open masses of sandstone and schists beneath 
the calcareous flagstones. This section, as exhibited near Pont Ladies, on 
the left bank of the Towy, deserves notice. There the following beds dip 
to the E. by S. at an angle of 75°. 
1st. Dark schists with sandstone courses, which graduate upwards into thin 
schists with nodules. 2nd. Strong bands of hard siliceous light-coloured grits, 
alternating with thin courses of black shale or schist, which, predominating up- 
wards, contains some remains of Trilobites. 3rd. Calcareous grits and pebble- 
beds, with remains of Orthidse and Corals, followed by schists in which Asaphus 
tyrannus is conspicuous, the group being covered by hard siliceous grits, the 
masses of which are full of Annelide-trails and of concretions. 4th. Calcareous, 
dark-coloured, finely laminated flagstones and schists, similar to those at Llan- 
