120 Dr. C. Callaway—Pre-Cambrian Geology of Anglesey. 
« Altered Cambrian,” surrounded by “granite,” on the Survey Map. 
The most southerly point in this area at which J have observed the 
schist is at Ty newydd, half a mile south of the Holyhead Road, and 
it disappears under the granitoidite at the north-east extremity of the 
ellipse near Seri fach, one mile and a half east of Llechyn farwy, in 
the very centre of the granitoid band. Its axis lies a little west of 
the craggy ridge of Craig yr Allor. 
Proof of the Anticlinal (Fig. 1). 
Commencing at the south end, we find at Bwleyn, north-west of 
Llanbeulan, quartzose .chloritic schist with a high $.S8.E. dip. At 
Ty newydd, one-third of a mile to the west, the rock is similar. 
Coming round to the north-west to the north of the Holyhead Road, 
we find, at another Ty newydd (Note 1, p. 126),' an exposure of 
dark gneiss with folia planes dipping at a low angle to the W.S.W. 
A mile to the N., at Clegyr gwynion, I obtained the first clear 
proof of the infraposition of the schist. Approaching the farm, the 
foliation lines are seen striking to the S.E. across the road. Climb- 
ing the wall to the right, I came upon a projecting crag composed 
of dark gneiss, very micaceous, interstratified with thin bands of 
nodular granitoid (Note 2, p. 126) rock. About three yards to the 
N.K. is another boss composed of similar material; but in this case 
the thin bands are of schist, the rock being mainly granitoid. The 
dip in these passage beds is at a moderate angle to the N.E. A few 
yards further on is a large craggy mass of granitoidite, in which I 
could detect no schistose intercalations. These rocks, it will be 
seen, show a deviation from the normal N.W. dip, and this is not 
the only locality in which I have noticed that the dome is disturbed 
or fractured. This is, of course, precisely what was to be expected 
in such a shattered district as Anglesey. Four hundred yards to 
the E., the gneiss dips to the N.W. A little further to the N.E. is 
contorted dark gneiss, with broad quartzo-felspathic folia dipping at 
a low angle to the N.W. and N.N.W. Higher beds, the strikes of 
which are seen at the junction of the two roads S. of Trefor, display 
the normal N.W. dip. Here also are seen nodular bands of granitoid 
rock. A mile N.E. of Trefor, E. of Llechyn farwy, hornblendic 
and micaceous schists are well exposed, dipping at a high angle to 
the N.W., and passing up through nodular passage beds into the 
granitoid rocks seen N. of the church. 
Coming round to the N.E. end of the dome, we find the very apex of 
the anticlinal. This is seen abouta mile S.E. of Llechyn farwy, at the 
second “e” of Pentre’r felin in the Ordnance Map, in a field E. of 
the road. The beds are bent into a perfect arch, and are composed of 
alternations of coarse and fine-grained dark-green gneiss, with a 
granitoid band in the middle. The axis of the anticlinal is seen to 
trend to the N.E. Granitoidite lies a few yards to the E. Follow- 
ing the axis to the N.E., we find in a quarry by a farm the 
The numbers within brackets refer to Prof. Bonney’s appendix (pp. 125-126). 
This rock looks like a hornblende-gneiss, but Prof. Bonney considers the dark 
mineral a mica. A great part of the upper gneiss seems hornblendic, but I have 
generally used the term ‘“‘dark”’ throughout this paper, in deference to his opinion. 
