564 Geological Society. 
their characteristic forms, the limestones of the Llandeilo formation 
expanding to greater thicknesses (Llanpeter-Felfry, Llandewi, &c.) 
than in any other part of their course, and containing many beautiful 
fossils, including two unpublished species of Trilobites, common to 
Caermarthenshire. The chief mass of the Silurian system ranges from 
E. to W. across the county, passing by Haverfordwest, till its western 
extremity subsides beneath the coal measures of Druson Haven and 
St. Bride’s Bay. Other bands of it rise from beneath the old red 
sandstone at Orlanton, Hoten, and Johnston ; whilst a most re- 
markable zone is heaved up in an anticlinal line extending across the 
most southern promontory of the county (Castle Martin Hundred), 
from Fresh Water East to Fresh Water West. The most perfect 
succession of the rocks of which the system is composed, is exhi- 
bited in the bold coast cliffs of Marloes Bay, extending for a distance 
of two miles, in which space the uppermost strata, rising at angles 
of 35° to 40° from beneath the old red sandstone of Hook Point, 
are succeeded by conformable, underlying masses, until the whole 
graduates down and passes into the rocks of the Cambrian system 
in Wooltack Park and Skomer Island. The Ludlow and Wenlock 
formations can be here defined; the latter containing many well- 
known fossils. The lower Silurian rocks are still more largely de- 
veloped; a vast thickness of fossiliferous sandy strata being quite 
identical with the “‘ Caradoc sandstones,” whilst the Llandeilo flags 
with Asaphus Buchit and A, Bigsbii (a new species of the author) 
occur in the haven called Moseley-wick Mouth. This coast section 
is 150 miles distant from the N. eastern extremity of the Silurian 
system. 
The Cambrian System.—If divided by a line passing from E. to W., 
the northern half of Pembroke is exclusively composed of the older 
rocks of the Cambrian system, consisting, in descending order, of 
a. Dark-coloured incoherent schists, with few stone bands, no cal- 
careous matter, and scarcely any traces of organic remains. 
These occupy a great breadth, and, as in Caermarthenshire, 
they form the beds of passage between the Silurian and the 
Cambrian systems (sometimes without any break). 
b. Hard grits and flagstones, coming strictly within the definition of 
greywacke of German mineralogists. 
c. Hard purple sandstones and schists, identical with the slaty grey- 
wacke of the Longmynd, Salop, (the Lammermuir hills, Scotland, 
may be cited as a good and well-known type of these rocks). 
d. Slates coarse and fine, with quartz veins and concretions. 
At St. David’s, Pantiphilip, and Scillyham, where the roofing-slates 
are quarried, the author has detected what he believes to be a coin- 
cidence between the laminz of deposit as indicated by differently co- 
loured layers of sediment, and the lines of slaty cleavage; though in 
the great majority of cases in Pembroke the rocks of this system, 
whether consisting of sandstone, schist, or hard slate, exhibit the di- 
vergences between the lines of true bedding and slaty cleavage, 
so clearly and ingeniously explained by Professor Sedgwick. The 
author therefore thinks it right to point to these exceptions to the 
