CHAPTER II The Nature and Causes of Volcanic Action--Modern Volcanoes 10 CHAPTER III Ancient Volcanoes: Proofs of their existence derived from the Nature of the Rocks erupted from the Earth's Interior. A. Materials erupted at the Surface--Extrusive Series. i. Lavas, their General Characters. Volcanic Cycles. ii. Agglomerates, Breccias and Tuffs 14 CHAPTER IV Materials erupted at the Surface--Extrusive Series--_continued_. iii. Types of old Volcanoes--1. The Vesuvian Type; 2. The Plateau or Fissure Type; 3. The Puy Type. iv. Determination of the relative Geological Dates of Ancient Volcanoes. v. How the Physical Geography associated with Ancient Volcanoes is ascertained 39 CHAPTER V Underground Phases of Volcanic Action. B. Materials injected or consolidated beneath the Surface--Intrusive Series: I. Vents of Eruption--i. Necks of Fragmentary Materials; ii. Necks of Lava-form Materials; iii. Distribution of Vents in relation to Geological Structure-Lines; iv. Metamorphism in and around Volcanic Cones, Solfataric Action; v. Inward Dip of Rocks towards Necks; vi. Influence of contemporaneous Denudation upon Volcanic Cones; vii. Stages in the History of old Volcanic Vents 52 CHAPTER VI Underground Phases of Volcanic Action--_continued_. II. Subterranean Movements of the Magma: i. Dykes and Veins; ii. Sills and Laccolites; iii. Bosses (Stocks, Culots), Conditions that govern the Intrusion of Molten Rock within the Terrestrial Crust 77 CHAPTER VII Influence of Volcanic Rocks on the Scenery of the Land--Effects of Denudation 100 BOOK II VOLCANIC ACTION IN PRE-CAMBRIAN TIME CHAPTER VIII Pre-Cambrian Volcanoes The Beginnings of Geological History--Difficulties in fixing on a generally applicable Terminology--i. The Lewisian (Archæan) Gneiss; ii. The Dalradian or Younger Schists of Scotland; iii. The Gneisses and Schists of Anglesey; iv. The Uriconian Volcanoes; v. The Malvern Volcano; vi. The Charnwood Forest Volcano 109 BOOK III THE CAMBRIAN VOLCANOES CHAPTER IX Characteristics of the Cambrian System in Britain