I. Introductory Remarks. The principal exposures of the Lower Palaeozoic and associated rocks are found in the sea-cliffs which extend for nearly 20 miles westward from Tramore to Ballyvoyle Head, and along the banks of the Suit near Passage. Inland the outcrops are much obscured by Drift, and consequently the best opportunity of determining the succession, etc. is afforded by the coast-sections, which will therefore be here described. The complexity of many of these sections is considerable, and is mainly caused by the intrusion of various later igneous rocks, as Sir A. Geikie has remarked. Historical Summary. The earliest geological account of the region was published by Thomas Weaver in 1821, in his paper on the ‘Geological Relations of the East of Ireland,’ but no details were given. In 1824 the Rev. R. H. Ryland's ‘History, Topography, & Antiquities of the County & City of Waterford’ appeared, in which we find many references to the rocks and mines (pp. 255, 258, 273). The paper by J. Hodgson Holdsworth 3 in 1833 on the ‘Geology of the District of the Knockmahon Mines’ is specially interesting from its record of the discovery of fossils in the ‘slate-rock’ near Knockmahon. In 1837 Weaver 4 published a paper on the ‘Geological Relations of the South of Ireland,’ in which he gave an account of the ‘Transition rocks,’ enumerating the different lithological varieties and mentioning the occurrence of fossils in a cliff east of the Bonmahon river and also inland. Sir R. Griffith mentioned the