54 
SILUEIA. 
[Chap. Ill 
In quitting this dislocated part of the west coast of Pembrokeshire, and 
advancing from Haverfordwest to the borders of Carmarthenshire, the ge- 
ologist perceives that the upper member of the Llandeilo formation puts on 
a much more calcareous structure. The schists and dark roofing-slates of 
the Precelly Hills graduate into calcareous flags, which at Llandewi Felfry 
and Lampeter Felfry become thick argillaceous subcrystalline dark-grey 
rocks, traversed by veins of white calc-spar, and constituting fine masses 
of limestone. These beds are largely worked for lime, and are, as far as 
I know, the only Lower Silurian rocks in Wales now used for such a pur- 
pose. The student will have, learnt from the previous pages, tbat through- 
out all the masses underlying the Llandeilo formation there is little cal- 
careous matter, and an accompanying deficiency of shelly animal remains. 
In these Llandeilo rocks, however, the original conditions having under- 
gone a considerable change, many more fossils occur. The relations of the 
strata are here given. 
Section at Llandewi Felfry, Pembrokeshire. 
S.S.E. N.N.W. 
b. Llandeilo schists; and b 2 
limestones. 
q £2 b b 2 b b 2 c c ' Caradoc beds. 
Underlain by a considerable thickness of black schist (b), and sur- 
mounted by other strata (c), which contain, as will presently be shown, a 
different group of organic remains belonging to the Caradoc formation, 
the massive limestones (6 2 ) of this section are charged with Ogygia, Asa- 
phus, Calymene, Trinucleus, Lingula attenuata, and L. granulata, above 
figured(p. 51), together with Leptsena sericea, Orthis striatula, and the well- 
View from Dynevor Park, Llandeilo, looking to the Hills above 
Golden Grove. (From Sil. Syst. p. 347.) 
known Chain-coral, Halysites catenulatus — a fossil which also pervades 
all the superjacent Silurian limestones of Caradoc, Wenlock, or Ludlow 
