542 H. HICKS ON THE PRE-CAMBRIAN 
belonging to series d, the basic tuffs, &e. These lie in true order of 
succession on the series ¢ above described. These tufts are largely 
made up of fragments of diabase, as may be seen from Note 36 
from a specimen from Carn-ar-wig, and Note 37 from the same 
series east of Castell to the north. Note 35 refers to the dark green 
compact rock exposed at the old copper-mine at Pen-maen-melyn ; 
a much altered felspathic diabase. To the east of Castell the 
basic rocks become exposed in several rugged knolls; other knolls to 
the 8.E. are found to consist of the schistose rhyolites and breccias 
of series c. In the line of the section, fig. 9, which is taken from 
Castell, in Ramsey Sound, in an E.S.E. direction to Porth-clais, the 
Cambrian conglomerates are shown reposing unconformably on the 
basic series d. They can be seen in this position in the field to the 
east of Castell, having, between Ogfeydd-duon and this point, a dis- 
tance less than a quarter of a mile, crept over the edges of a con- 
siderable thickness of the Pre-Cambrian beds. The unconformity 
shown in fig. 14 is most marked, and it is perfectly evident that 
Fig. 14.—Cliff-section between Castell and Ogfeydd-duon, showimg 
unconformity of Cambrian on Pebidian. 
a 
p. 
Pebidian. 
the conglomerates are constantly reposing in this area on different 
members of the underlying Pebidian series. Moreover, we have 
proofs in abundance here, as in the sections near Nun’s Chapel in 
St. Bride’s Bay, to show that the Pebidian rocks were in their 
present condition before the Cambrian rocks were deposited, as 
shown by the fragments contained in the latter. Some of these are 
mentioned in the Notes 65-70. Fragments of the basic tufts d, and 
of the schistose rhyolites ¢, are plentiful in the Cambrian con- 
glomerates in these areas, and many of the rolled pebbles of these 
rocks are of large size. 
6. Whitesand Bay, Rhosson, Clegyr Foig, &e. 
In this area the rocks for the most part are like those described 
in the section to the south, fig. 9, but higher beds of the Pebidian 
become exposed as the Cambrian conglomerates are followed to 
the north. By a strange error, the Cambrian conglomerates are 
shown, in the Director-General’s map, to strike inland at a distance 
of more than a quarter of a mile to the east of Porth-seli, while in 
