Under The Microscope

THE MACMILLAN FIELD GUIDE TO GEOLOGICAL STRUCTURES by John L. Roberts; Macmillan, 1996; 250 pages; $29.95

This book has been written with the layperson as well as the student of geology in mind. It is clearly set out in six parts each consisting of small, clearly labelled chapters.

The first and second parts deal with three classes of rock covering the nature of each class and the characteristic structures associated with them, and the various processes that affect them over time.

In the third and fourth part, the book describes some of these processes in more detail looking at unconformities and their use in dating of rocks and understanding physical structures, plate tectonics, and faulting, folding, thrust zones and so on. Part Five zeroes in on the structural relationships of folded rock formations, discussing minor and major folds, anticlynes and synclines, amongst others. Up to here this portion of the book has been mainly dealing with structures resulting from earth movements affecting sedimentary rocks or their metamorphic equivalents. Part Six moves on to looking at the rocks underlying these layers of sedimentary and metamorphic rock -- migmatites and basement gneisses.

An appendix lays out guidelines for the student undertaking structural fieldwork, giving instructions on the measurement and mapping of rock types, faults and other structures. A second appendix lists the locations of the illustrations used throughout the book.

Although this book is produced as a field guide, I would not recommend it to the family out for a Sunday afternoon walk in the country. Although the author takes care to define the terms he uses, the text assumes a background in geological study. Also the typeface is rather small making it hard to read at a glance. However, colour photographs and clear line drawings are used throughout to illustrate the various structures and the book is well set out.

I feel that this book is well suited to a tertiary student studying geology and geomorphology, and to interested laypeople with some background in the topic and would recommend it as an inexpensive addition to their reference libraries. However be aware that the book has been written and published in England, and all the illustrations are taken from Great Britain.

Ros Davis majored in physical geography from Canterbury University.