Vast lapse of time between the close of the Palæozoic and beginning of the Tertiary Volcanic Eruptions--Prolonged Volcanic Quiescence--Progress of Investigation among the Tertiary Volcanic Series of Britain 107 CHAPTER XXXIV The System of Dykes in the Tertiary Volcanic Series Geographical Distribution--Two Types of Protrusion--Nature of component Rocks--Hade--Breadth--Interruptions of Lateral Continuity--Length--Persistence of Mineral Characters 118 CHAPTER XXXV The System of Dykes--_continued_ Direction--Termination upward--Known vertical extension--Evidence as to the movement of the Molten Rock in the Fissures--Branches and Veins--Connection of Dykes with Intrusive Sheets--Intersection of Dykes--Dykes of more than one infilling--Contact metamorphism of the Dykes--Relation of the Dykes to the Geological Structure of the Districts which they traverse--Data for estimating the Geological Age of the Dykes--Origin and History of the Dykes 145 CHAPTER XXXVI The Plateaux Nature and Arrangement of the Rocks: 1. Lavas.--Basalts, Dolerites, Andesites--Structure of the Lavas in the Field--2. Fragmental Rocks.--Agglomerates, Conglomerates, and Breccias--Tuffs and their accompaniments 181 CHAPTER XXXVII The Several Basalt-Plateaux and their Geological History--Antrim, Mull, Morven and Ardnamurchan 199 CHAPTER XXXVIII The Basalt-Plateau of the Parish of Small Isles--Rivers of the Volcanic Period 215 CHAPTER XXXIX The Basalt-Plateaux of Skye and of the Faroe Isles 249 CHAPTER XL The Modern Volcanoes of Iceland as illustrative of the Tertiary Volcanic History of North-Western Europe 260 CHAPTER XLI The Eruptive Vents of the Basalt-Plateaux Vents filled with Basalt or other Lava-form Rock--Vents filled with Agglomerate 270 CHAPTER XLII The Basic Sills of the Basalt-Plateaux 298 CHAPTER XLIII The Bosses and Sheets of Gabbro Petrography of the Rocks--Relations of the Gabbros to the other members of the Volcanic series--Description of the Gabbro districts--Skye 327 CHAPTER XLIV