1872..
HICKS- — TREMADOC ROCKS.
41
stratified with grey flaky slate containing LinguleUa Davisii in great
abundance. They graduate by almost insensible degrees from these
as hard grey flags, then bluish grey, with some thick-bedded rock of
tough texture. They have a thickness of nearly 1000 feet, with an
average dip of about 60°, and the strike of the beds is from N.E. to
S.W. They form the north-east point of the island, and are exposed
in an excellent coast-section, with the Lingula-fiags dipping under
them, and the dark iron-stained Arenig slates resting upon them.
It is doubtful, however, whether the latter rest conformably upon
them. I am inclined to think that a fault intervenes, and that the
proper thickness, as shown at some of the other places, does not
occur here in consequence.
Fig. 2. — Section across the northern part of Ramsey Island (see Map).
W. Fault. E.
5. Lingula-flags.
6. Tremadoc rocks.
7. Arenig rocks.
At "Whitesand Bay they also rest conformably on Lingula-flags ;
but a fault running up in a north-east direction, and almost in the
strike of the beds, has removed more than three fourths of their
thickness, and has brought down the Arenig group in contact with
them, so as to give it an appearance of resting almost conformably
upon them. Further north, near Llanveran, the fault has gone
eastward of the series, and they are seen again in nearly their entire
thickness underlying the Arenig group.
The third patch, at Tremanhire, in the middle of the country,
east of St. David's, occupies a greater area ; but there are only a
few quarries open, and therefore considerable difficulty has been
experienced in defining its proper limits. The Lingula-flags seem
everywhere to underlie the series here as at the other places ; but
the Arenig rocks only come in unconformably at the N. E. end of
the patch. The beds have very much the same character as at
Ramsey Island, with the exception that the middle portion is more
of a sandstone in parts, and less cleaved. Some of the most perfect
specimens have been found in these last-mentioned beds near and at
a place called Paran on the map.
On the whole, however, Ramsey Island offers the hest advantages
for examining these rocks, and also for obtaining fossils, as the beds
are there well exposed, and literally, in some parts, almost entirely
made up of organic remains.
The species which have been discovered in these rocks, with the
exception of LinguleUa Davisii, are all new, as well as a few of the
genera. They comprise a new genus of Trilobites, which I have
named Neseurctus, and of which there are several species. This