File:The Quarterly journal of the Geological Society of London (14075866545).jpg

ROCKS OF PEMBEOKESHIEE.
543
reality they are the rocks which form the cliffs for a considerable
distance along the east shores of that harbour. This same strange
mistake is evident also in his section, as a most abnormal thickness
is given to the sandstones above the conglomerates, to enable the
other beds to get into position. It certainly is a curious fact that
the greatest exposure of Cambrian conglomerates in the neighbour-
hood of St. David's should be thus missed, as it evidently must have
been, by the Director-Greneral. This error of his furnishes the best
proof that could be desired of the great unconformity between the
Cambrian conglomerates and the Pebidian; for had the former con-
tinued to lie on the same beds of the latter as at Ehosson, less than
a mile to the south, where they are well exposed, their position
would be a quarter of a mile to the east of Porth-seli, as shown in Dr.
Geikie's map. The facts, however, as stated above, prove that in this
mile of country a quarter of a mile in thickness of nearly vertical Pebi-
dian strata has been overlapped by the conglomerates. The sketch,
fig. 15, shows the Cambrian conglomerates reposing upon the Pebidian
I'ig. 15. — Shetch of Cliffs on south side of Ogof-golchfa, WTiitesand
Bay^ showing basal Cambrian Conglomerate (1) resting uncon-
formably on Pebidian rocks (series e).
Index as in Map, PL XXIV.
beds at Ogof-golehfa, Whitesand Bay. The conglomerates are of very
great thickness here, the pebbles of large size, and many of the frag-
ments are such as could only be derived from the Pebidian beds
below. The large pebble exhibited by me at the meeting, when the
second part of Prof. Geikie's paper was read, which was claimed by
Mr. Peach to be a segregation, came from these beds ; and 'Note 69
will show that it is a large pebble of a schistose quartz-felsite
identical with the quartz-felsites of series c of the Pebidian. The
conglomerates at Ogof-golchfa repose upon schistose felsitic tuffs
and breccias, and some schistose argillites. Notes 39 and 40 refer
to some of these rocks.
Section, fig. 1 (p. 524), runs in a S.E. direction from the south
side of Porth-seli across the Pebidian rocks and the Dimetian
axis to the shore of St. Bride's Bay below Nun's Chapel. It
shows the usual series of Cambrian rocks in this area, and the
Pebidian series as in the section to the south, but with a greater