618 MR. E. GREENLY ON THE GEOLOGY OF THE [NOV. 1 896, 



36. The Geology of the Eastern Corner of Anglesey. By Edward 

 Greenly, Esq., F.G.S. (Read June 10th, 1896.) 



Contents. 



Page 



I. Introduction 618 



II. Careg Onen Slates 618 



III. Baron Hill or Bangor Group 623 



IV. Ordovician Series 626 



V. The Carboniferous Rocks (and Dykes) 628 



VI. Glaciation 629 



VII. Summary 631 



I. Introduction. 



The observations recorded in this paper were made during a 

 detailed survey on the 6-inch scale, by myself, of a small portion 

 of Anglesey. It is my intention to continue the mapping of the 

 island on the same scale. 



I should like to express my thanks to former workers upon 

 Anglesey, all those with whom I have come into communication 

 having expressed the warmest sympathy with my undertaking ; and 

 in particular to my former chief, Sir Archibald Geikie, and to Prof. 

 Bonney, who have aided me very substantially by generous loans 

 of slides and specimens. 1 My friend and late colleague, Mr. Peach, 

 has also, with his wonted goodness, looked over the graptolites and 

 other fossils for me. Dr. G. J. Hinde and Prof. T. Rupert Jones have 

 been so kind as to determine certain small organisms ; and to 

 Mr. G. J. Williams I am indebted for the photograph of the slates 

 at Careg Onen. 



II. Careg Onen Slates. 



The Carboniferous Limestone and Ordovician shales form the 

 greater part of the cliffs about the cove of Careg Onen 2 (fig 1), but 

 near the western end of the beach we find, emerging from beneath the 

 latter, a series of hard, greenish, fissile rocks dipping apparently at 

 very high angles (figs. 1, 2 & 3). Careful examination, however, re- 

 veals indistinct planes of bedding, crossing the conspicuous divisional 

 planes — which are really planes of cleavage — at various angles, and 

 evidently much folded (fig. 4, p. 620). There are some lines of dark 

 nodules following the bedding : some zones are gritty, and there are 

 others of hard, compact argillite, scarcely cleaved, which contain 

 a few oolitic grains. 



1 I am preparing an Index of Anglesey Literature, which I hope to make 

 exhaustive. In these pages, therefore, passing reference only will be made to 

 the principal papers on the area. 



2 Careg Onen is the name of the cove about ^ mile north-west of Bwrdd 

 Arthur. It has no name on any of the maps. This, and many other names 

 desirable for reference, will, I hope, be soon inserted in new editions of the 

 Ordnance maps. 



