578 C. CALLAWAY ON THE ARCHZAN AND 
On its western side, at the distance of a few feet, runs a parallel 
elevation of pale-green slate, with veins of a green mineral like 
epidote. The slaty rock is not clearly stratified, but planes which 
may represent bedding dip westerly. This band extends further 
to the south than the granitoidite, and, just where the older ridge 
would underlie if it were continued to the south, as is most probably 
the case, the slate contains pebbles (shown above 6 in fig. 9) of 
granitoid rock, of the same general type as that which forms the 
ridge (Nos. 114, 115, pp. 584, 585). 
Resting on the granitoid axis on its eastern flank, and in actual 
contact with it, crops out the Llanfihangel conglomerate and grit, 
dipping easterly at 50°. At the base (Nos. 124, 125, p. 587) is 
grit which can hardly be distinguished in the field from a granitoid 
rock; but the presence of very small pebbles of a soft schist 
determines its derivative origin. Within a few yards (No. 126, 
p. 587), it becomes very distinctly fragmental, but is still largely 
composed of the constituents of granite. It then passes up into 
the ordinary green conglomerate and grit (No. 127, p. 587). 
A few yards to the south of the granitoidite, the conglomerate 
reappears, resting immediately on the green slate with granitoid 
pebbles (fig. 9), the surface of the slate sloping easterly, in 
accordance with the dip of the grit in the northern ridge. The 
conglomerate does not display clear dip. It is very coarse, 
containing large pieces of the green slate (No. 116, p. 585), with 
smaller fragments of gneiss (Nos. 120-123, p. 586), a variety 
largely made up of hornblende being conspicuous. No. 120 is 
from the junction of the slate with the hornblendic conglomerate, 
and includes both. 
A great deal of the conglomerate about here is composed of 
gneissic fragments ; but, strange to say, though the green Holyhead 
schist occupies the area to the west, its outcrop appearing within 
fifty yards of the ridge, I have not been able to detect a single 
fragment of it in the conglomerate. There is plenty of a green 
altered rock; but, so far as I have observed, it is all of ordinary 
Pebidian types. 
The Holyhead schist is separated from the ridge just described by 
a small hollow. As the dip of the schist is north-westerly, it might 
seem as if it overlay the granitoidite in regular sequence. But to 
this view there are the following objections :-— 
1. The green schist is, in central and eastern Anglesey; conformably 
underlain by thin-bedded grey gneiss, quite unlike the massive 
granitoid rock of the Tywyn ridge. 
2. The granitoidite of our section is immediately succeeded on the 
west by the slaty rock, which is almost unaltered; and it is nearly 
incredible that it should directly underlie, without beds of passage, 
so highly metamorphosed a rock as the Holyhead schist. 
3. If the green schist were in sequence above the granitoidite, it 
must have been above water when the Llanfihangel conglomerate 
was formed ; and asit lies withina stone’s throw of ‘the conglomerate 
it would almost certainly have supplied it with fragments. But 
