The woodcuts which illustrate the volume are in some cases prepared from photographs, and I am indebted to Mr. Cooper for the skill with which he has carried out my wishes concerning their reproduction. Others among the engravings are copies of sketches which I made in Italy, Hungary, Bohemia, and other volcanic districts. The whole of the wood-blocks employed by Mr. Poulett Scrope in his work on Volcanoes were placed at my disposal before his death, and such of them as were useful for my purpose I have freely employed. To Captain S. P. Oliver, R.A., I am obliged for a beautiful drawing made in the Island of Bourbon, and to Mr. Norman Lockyer and his publishers, Messrs. Macmillan & Co., for the use of several wood-blocks illustrating sun-spots and solar prominences. J. W. J. London: _May 1881_. CONTENTS. CHAPTER I. PAGE INTRODUCTORY: NATURE OF THE ENQUIRY 1 CHAPTER II. THE NATURE OF VOLCANIC ACTION 7 CHAPTER III. THE PRODUCTS OF VOLCANIC ACTION 39 CHAPTER IV. THE DISTRIBUTION OF THE MATERIALS EJECTED FROM VOLCANIC VENTS 67 CHAPTER V. THE INTERNAL STRUCTURE OF VOLCANIC MOUNTAINS 112 CHAPTER VI. THE VARIOUS STRUCTURES BUILT UP AROUND VOLCANIC VENTS 161 CHAPTER VII. THE SUCCESSION OF OPERATIONS TAKING PLACE AT VOLCANIC CENTRES 186 CHAPTER VIII. THE DISTRIBUTION OF VOLCANOES UPON THE SURFACE OF THE GLOBE 224 CHAPTER IX. VOLCANIC ACTION AT DIFFERENT PERIODS OF THE EARTH'S HISTORY 247 CHAPTER X. THE PART PLAYED BY VOLCANOES IN THE ECONOMY OF NATURE 281 CHAPTER XI. WHAT VOLCANOES TEACH US CONCERNING THE NATURE OF THE EARTH'S INTERIOR 307