doubt as to their being of the same general age as the rocks with which they are associated, and therefore presumably Precambrian. The Pembrokeshire rocks are marked by the occurrence of a certain amount of metamorphism, probably of more than one kind, which has converted pyroclastic volcanic rocks into sericitic-schists and quartz-felsites into hälleflintas[56]. The term Pebidian given by Dr Hicks to the contemporaneous volcanic fragmental rocks should be retained, and if these rocks be eventually shewn to be contemporaneous with similar volcanic rocks of other districts, may be applied generally, as it has priority over other terms as Uriconian and Caldecote series. The term Dimetian was applied to rocks known to be intrusive, and must be dropped as a chronological term, whilst the existence of an Arvonian system separate from the Pebidian system is not fully proved. [Footnote 52: The reader may consult a paper by Prof. Lapworth "On _Olenellus Callavei_ and its geological relationships," _Geol. Mag._ Dec III. vol. VIII. p. 529, for information concerning the relationship of the _Olenellus_ beds of Shropshire to the more ancient rocks; the Uriconian rocks are described by Dr Callaway in a series of papers, especially in the _Quarterly Journal of the Geological Society_, vol. XXXV. p. 643, vol. XXXVIII. p. 119, vol. XLII. p. 481 and vol. XLVII. p. 109, whilst the lithological characters of the Longmyndian rocks are described by the Rev. J. F. Blake (_Quart. Journ. Geol. Soc._, vol. XLVI. p. 386).] [Footnote 53: See Lapworth, C., "On the sequence and systematic position of the Cambrian rocks of Nuneaton," _Geol. Mag._ Dec III. vol. III. p. 319; and Waller, T. H., "Preliminary Note on the Volcanic and Associated Rocks of the neighbourhood of Nuneaton," _ibid._ p. 322.] [Footnote 54: For details concerning the rocks of the Malvern Hills see papers by Callaway in the _Quarterly Journal of the Geological Society_, vol. XXXVI. p. 536, XLIII. p. 525, XLV. p. 475, and XLIX. p. 398, and a paper by Prof. A. H. Green, _ibid._ vol. LVI. p. 1.] [Footnote 55: Callaway, C., _Quart. Journ. Geol. Soc._, vol. XXXV. p. 643.]