Learning from N.Z. rocks

Press, 8 February 1986, Page 20

Learning from N.Z. rocks

Ffe/d Guide to New Zealand Geology. By Jocelyn Thornton. Reed Methuen, 1985. 218 pp. Index. $29.95. (Reviewed by Howard Keene) Every year the New Zealand landscape is tramped and driven over by hundreds of thousands of people from home and abroad, but how many understand its formation? The “Field Guide to New Zealand Geology” fills an important gap in a small, but growing number of books on New Zealand geology which are accessible to the general public. It is a travellers’ guide for those who are interested in rocks, especially collectors of fossils and minerals. However, it goes much further than being just a rockhounds’ directory; it provides a clear geologic history of New Zealand which the reader can trace from the evidence shown in roadside, stream, and cliff exposures. This book succeeds in treading a fine line, because it will appeal to beginners, and yet it should be useful to a geologist visiting an unfamiliar area. The introductory chapter outlines the basics of geology, and when new concepts are introduced later in the book it is in an unlaboured way so as not to bore more knowledgeable readers. A geologic history of New Zealand makes up the bulk of the text, and this falls neatly into three phases — the three major phases of sedimentation which were brought to an end by

widespread upheaval. As a comprehensive history it is weakened somewhat by the emphasis on collecting specimens. For; example, the classic glacial sequences of the South Island, where there is little to take home but photographs, receive scant attention. To assist readers to find information quickly on areas they are visiting, maps of the North and South Islands are given at the beginning which show the main roads and the page numbers where descriptions of-the rocks in that area can be found. The author, gives specific information in the text to find important localities, but she is always mindful that some sites are of high scientific value and there are many warnings throughout the book. The “Field Guide” is liberally illustrated with colour and black and white photographs, maps, diagrams, and thumb nail sketches, but especially notable are the fresh, soft pencil or charcoal drawings of fossils and minerals, and for serious students the drawings of fossils which are indicators of the different geologic stages will be useful. For example the various species of the bivalve Inoceramus, which distinguish between the stages of the Cretaceous Period, are shown, together on one page. The “Field Guide” is well worth reading straight through, but its true value will become apparent in having it with you in the car on those trips planned for the future.