Welsh Journals

THE GEOMORPHOLOGY OF BRECKNOCK BY TREVOR M. THOMAS, M.SC., F.G.S., F.R.G.S. Research Officer, Welsh Office, Ministry of Housing and Local Government, Cardiff. I. INTRODUCTION II. STRUCTURAL COMPONENTS AND PRE-TERTIARY GEOLOGICAL HISTORY (a) The Rock Systems of Brecknock i Ordovician ii Silurian iii Old Red Sandstone iv Carboniferous (b) Structural Grain of the County (c) Geological History and Palaeogeography (d) The Inherited Structural Control of Scenery III. THE EVIDENCE FOR TERTIARY PLANATIONS IN THE EXISTING LANDSCAPE PATTERN IV. THE EVOLUTION OF THE DRAINAGE SYSTEM (a) The Hypotheses of Strahan (1902) and Lake (1934) (b) Application of these Theories to the Rivers of Brecknock (c) Regional Descriptions of Individual River Systems (i) The Wye Basin (ii) The Upper Towy, Upper Irfon and Upper Usk Systems (iii) The Rivers of the Black Mountains (iv) The Upper Tawe System (v) The Upper Neath Tributaries V. GLACIATION AND GLACIATED LANDFORMS (a) The Northern Plateau (b) The Builth-Llanwrtyd Depression