Vol. 55.] THE GEOLOGr OF NOETHERN ANGLESEY. 635 



35. On the Geology of Northern Anglesey. By C. A. Matley, 

 Esq., B.Sc, F.G.S. With an Appendix on the Microscopic 

 Study of some of the Rocks, by Prof. W. W. Watts, M.A., 

 Sec.G.S. (Read June 7th, 1899.) 



Contents. 



Page 

 I. Introductory Eemarks 635 



II. Description of the Rocks 637 



(a) The Green Series. 



{b) The Northern Complex. 



(c) The Ordovician Rocks. 



III. Relation of the Green Series to the Ordovician 638 



(a) Palffiontological Evidence. 



(i) Fossils north of the Green Series, 

 (ii) Notes on the Northern Fossils. 

 (iii) Fossils south of the Green Series. 

 (iv) Conclusions from the Palaeontological Evidence. 

 (6) Stratigraphical Evidence. 



(i) Nature of the Boundarj'. 

 (ii) Proofs of an Unconformity. 

 (c) Conclusion. 



IV. Earth-movements and their Effects 650 



(a) Contortions and Folds. 

 {b) Dislocations, 

 (c) Cleavage. 

 {d) Crushing, 

 (e) Disruption. 



(/) The Crush-Breccias and Crush-Conglomerates, 

 (i) Trwyn Pen-careg. 

 (ii) Porth y Corwgl. 

 (iii) The Cemaes District. 

 (iv) Western part of the North Coast. 

 (v) Dykes in the Crush-Zones, 

 (vi) Method of Formation. 

 {g) Age of the Movements. 



V. The Northern Complex and its Relation to the Ordovician... 667 

 (a) Limestones. 



{b) Quartzites and ' Quartz-Knobs.' 

 (c) The Ordovician Rocks. 

 {d) Relation of the Northern Complex to the Ordovician. 



VI. Summary 674 



VII. Appendix on the Microscopic Study of some of the Rocks ... 675 



I. Introductory Remarks. 



The northern part of Anglesey contains a group of rocks regarding 

 the age of which geologists hold divided opinions. As the well- 

 defined district in which they lie occupies the north of the island, 

 the strata taken as a whole are known as the ' Northern District 

 Rocks.' From their frequently twisted and contorted aspect, 

 Prof. Hughes calls them the ' Gnarled Series.' These beds have a 



