Variant spelling, inconsistant hyphenation and inconsistant use of ligatures, have been retained.

The errata listed on a slip bound into this book have been applied to this text. The errata slip is transcribed at the end of the book. One missing full stop has been added, a duplicate word has been deleted, but otherwise the book is as printed.

Figures have been moved to be near the text they illustrate. The page numbers in the Table of Illustrations refer to the page number of their original position in the printed book. The text of the diagram of Geological Systems is given at the end of the book.