CHAP. XIII 
ANGLESEY 
225 
Carmel Point, the section may be seen which is shown in Fig. 61. Here 
the blue or lead -coloured shale or slate (a) marked as Silurian on the 
Geological Survey map passes up into a mass of fine yellowish felsitic tuff 
and breccia (6). The shale at the junction intercalates in thin leaves with 
the tuff. 
The breccias south of Carmel Point, though they are chiefly made up 
of felsitic detritus, sometimes show a preponderance of fragments of shale. 
They vary also rapidly in texture and composition. These variations may 
indicate that the vent or vents from which their materials were derived 
stood somewhere in the near neighbourhood, if indeed they are not to be 
recognized in some of the boss -like eminences that rise above the shore. 
At the same time, the enormous amount of crushing and shearing which 
Fig. 61. — Blue shale or slate passing into volcanic breccia east of Forth Padrig, near Carmel 
Point, Anglesey. 
the rocks of this region have undergone has doubtless introduced crush- 
conglomerates into the structure of the ground. And some patient labour 
may he rerpiired before the nature and oiigin of the different fragmental 
masses are determined. 
Certain remarkably coarse, tumultuous breccias, exposed on the coast at 
Mynyddwylfa and Ceramaes, were formerly regarded by me as volcanic 
agglomerates. But more recent examination has satisfied me that these, 
like the breccias at Llangefni, are not of volcanic origin but are crush- 
conglomerates.^ 
While the lower breccias are sometimes tolerably coarse, the volcanic 
detritus becomes much finer in the higher parts of the Amlwch slates. Above 
the limestones and black shales of Cemniaes volcanic breccias and ashes, 
with limestone, quartzite, conglomerate and thin seams of black shale, con- 
tinue to the extreme northern headlands. The amount of fine volcanic 
detritus distributed through these strata is very great. We can clearly make 
^ Presidential Address, Quart. Jouri. Geol. Soc. vol. xlvii. p. 134 ; Itup. Brit. Assoc. 1896, 
Section C; Geot. Mag. 1896, p. 481. 
VOL. I 
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