The Physical Geography of the Cambrian Period--The Pioneers of Palæozoic Geology in Britain--Work of the Geological Survey in Wales--Subdivisions of the Cambrian System in Britain 139 CHAPTER X The Cambrian Volcanoes of South Wales 145 CHAPTER XI The Cambrian Volcanoes of North Wales, the Malvern Hills and Warwickshire 159 BOOK IV THE SILURIAN VOLCANOES CHAPTER XII Characters of the Silurian System in Britain. The Arenig Volcanoes The Land and Sea of Silurian time--Classification of the Silurian System--General Petrography of the Silurian Volcanic Rocks--I. The Eruptions of Arenig Age 173 CHAPTER XIII The Eruptions of Llandeilo and Bala Age i. The Builth Volcano--ii. The Volcanoes of Pembrokeshire--iii. The Caernarvonshire Volcanoes of the Bala Period--iv. The Volcanic District of the Berwyn Hills--v. The Volcanoes of Anglesey--vi. The Volcanoes of the Lake District; Arenig to close of Bala Period--vii. Upper Silurian (?) Volcanoes of Gloucestershire 202 CHAPTER XIV The Silurian Volcanoes of Ireland 239 BOOK V THE VOLCANOES OF DEVONIAN AND OLD RED SANDSTONE TIME CHAPTER XV The Devonian Volcanoes 257 CHAPTER XVI The Volcanoes of the Old Red Sandstone Geological Revolutions at the close of the Silurian Period Physical Geography of the Old Red Sandstone--Old Lake-basins, their Flora and Fauna--Abundance of Volcanoes--History of Investigation in the Subject 263 CHAPTER XVII Distribution of the Volcanic Centres in the Lower Old Red Sandstone--Characters of the Materials Erupted by the Volcanoes 271 CHAPTER XVIII Structure and Arrangement of the Lower Old Red Sandstone Volcanic Rocks in the Field 281 CHAPTER XIX Volcanoes of the Lower Old Red Sandstone of "Lake Caledonia" Description of the several Volcanic Districts: "Lake Caledonia," its Chains of Volcanoes--The Northern Chain: Montrose Group--Ochil and Sidlaw Hills--the Arran and Cantyre Centre--the Ulster Centre 294 CHAPTER XX Volcanoes of the Lower Old Red Sandstone of "Lake Caledonia"--_continued_