On the Geology of Anglesey

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Abstract
The rocks to which these notes chiefly refer were described by Prof Henslow under the heads of Quartz Rock, Chlorite-schist and Grauwacke, in a paper read before the Cambridge Philosophical Society in 1821. He evidently considered them to be distinguishable members of one group, drawing attention to the passage from the quartzite into the schists, and to the generally coinciding dip of the clay slate and schists, even where, as at Porth Corwg, there is a small discordancy between the two, caused by a fault. He points out that green slates and brecciated conglomerates occur in the upper part of the black-slate group; but he records no fossils from which the geological horizon of the beds described can be determined, and his sections do not give much more than the geographical succession of the rocks over the areas referred to in this paper. Prof. Ramsay (Mem. Geol. Surv. vol. iii. p. 175) describes the Cambrian and Silurian Rocks of Anglesey as in great part resembling those of Caernarvonshire. The Cambrian rocks, he further remarks, are, as a rule, highly metamorphic, like those in the promontory of Lleyn (Cambrian in his nomenclature includes only the Harlech group). The Silurian ( i. e. the Lingula-flags and all above them), he goes on to say, are also sometimes metamorphosed into mica-schists and gneiss, while in other places they are rich in Caradoc or Bala and Llandeilo fossils. Unfortunately the genera and species of the Graptolites are not recorded except from one locality mentioned in

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