Pyroclastic rocks

240

careful to recognize the distinction between

familiar to a large number of geologists, are

shells in sediment and bleached shells ex-

summarized in this excellent book, which should prove valuable to both specialists and

posed on the ground surface, and the difficulty of determining the age of fairly young material is not ignored. Having established an impressive data

The authors are well qualified for this job. Both have impressive publication records

base, the author then employs this information to develop three related parts of the study. The first on " B i o g e o g r a p h y " is of use

and are very active in current research on pyroclastic rocks and processes. Chapters 2 to 4 discuss volcanoes,

to anyone studying the present-day distribu-

volcanic

tion of African plants or animals. It tells what is now known to be where, though the author

processes. Chapters 5 to 11 describe and interpret pyroclastic rocks, depositional

points out questions which need to be resolved. Next comes a summary of the Cretaceous and Tertiary history of the aquatic

mechanisms, and lithification processes. Chapters 13 and 14 summarize stratigraphic nomenclature and problems, and the tectonic

mollusks of the northern half of the continent. Again, this summary provides nuggets of information to geologists and paleontolo-

setting of pyroclastic rocks. The authors have sensibly restricted the range in topics, thus avoiding, for example, the usual narrations

gists which go beyond the limits of the title of the work; there is even a bit of pre-Cretaceous speculation. These two parts on 90 million years of

of famous historic eruptions. This focus has enabled them to write a comprehensive and detailed account of the features and origins of the rocks themselves. Although the book

shaping of the distribution patterns form a foundation for a summary of the Quaternary molluscan distribution. All parts of the book

is clearly aimed at students of post-graduate or advanced undergraduate level, it will also prove valuable to workers with some experi-

are impressive, but the admixture of climatology, archeology, geomorphology, and bi-

ence in the field. The references - I estimate about 1100

ology in this last section is a synthesis which

are among the best features of this b o o k

is going to be quoted for decades. A bibliography, register of localities, and two in-

non-specialists alike.

rocks,

magmas,

and

eruptive

Most date from the last two decades, but

dices complete the book. The volume will be of use to many groups of scientists who study Africa and its history.

they include several from the nineteenth century and many from 1 9 8 3 / 1 9 8 4 (in press). Although these provide much of the material discussed, the book is pervaded with

It is so comprehensive that it will be a standard reference in malacology and will have a long shelf life. There are a few typographical errors, mainly in capitalization, but they are

the authors' own interpretations and ideas, making reading stimulating and refreshing. The figures also are good all 339 of them. Most are reproduced from the refer-

inconsequential. The book good value for the money.

ences. Photographs are of excellent quality and mostly appear to be from the authors' own collections.

is remarkably

Ellis L. Yochelson, Washington, D.C.

PETROLOGY R.V. Fisher and H.-U. Schmincke, 1984. Pyroclastic Rocks. Springer-Verlag, Berlin, xiv + 472 pp., D.M.138.00, approx. U.S.$50. The publication of this work is timely, given the current surge in interest in pyroclastic rocks following the 1980 eruption of Mount St. Helens. Many new concepts, un-

One fault of this book is the lack of adequately concise and rigorous definitions of pyroclastic terminology. Although definitions are included, we are faced with inconsistencies. For example, on p. 8 we are told that hydroclastic eruptions are " t h o s e caused by vaporization of external water in contact with hot magma or lava", whereas on p. 233 we gather that such eruptions include, as a sub-category, phreatic (or hydrothermal) eruptions which involve no direct contact between erupted water and magma. This, and other inconsistencies in terminology (e.g. 'silicic' in Ch. 2, 'fetsic' in

241 Ch. 4, and 'felsitic' in Ch. 6) will be confusing to the non-specialist. A second fault lies in the tables, which appear throughout the book, which summarize rock characteristics and how they relate to depositional processes. These are an excellent idea, but in my view commonly contain oversimplifications and are misleading. They should be carefully reviewed prior to the next edition. O v e r a l l I c o n g r a t u l a t e Fisher and Schmincke on a thorough and professional job. Although at $50 this book is rather expensive, the individual may comfort h i m / herself in the knowledge that it will remain a leading source of information for several years to come. Tim Druitt, Menlo Park, Calif.

that is built around extensive compositional data for Jan Mayen rocks. As examples of the detail, Imsland's Cr-spinel discussion covers 21 pages that include tables and eight variation diagrams, and Fe-Ti oxides extend 30 pages with ten figures. Minor phases apatite and mica span 27 pages. His applica-. tion of major-element least-squares calcula-. tions to account for the differentiated alkalic suite is thorough and demonstrates diffi-. culties in accepting strict fractionation histories. The author concludes by putting Jan Mayen's origin into the context of North Atlantic tectonics. All of the lengthy mineralogy discussions are accompanied by references to mineral compositions in other volcanic provinces and e x p e r i m e n t a l results, thereby providing backgrounds helpful to readers researching new areas of interest or reviewing compositionat aspects such as A I - T i relationships in pyroxene, Sr distribution between plagioc-

P~ltl Imsland, 1984. Petrology, Mineralogy, and Evolution of the Jan Mayen M a g m a System. University of Iceland, Reykjavik, 332 pp.,

lase and liquid, or halogen contents of biotite and phlogopite. This is where I find the greatest value of this book. But more than

no price given (paperback).

that, it serves as a comprehensive data base for which petrography and whole-rock and

In his effort to publish a detailed petrologic study of an oceanic alkalic igneous province, author P&II Imsland inadvertently prepared a manuscript that doubles as a textbook for igneous mineralogy and fractionation processes. The study area is Jan Mayen Island in the upper North Atlantic Ocean, where a fully developed alkalic suite

mineral compositions of other oceanic provinces can be compared. Readers interested only in a casual understanding of Jan Mayen or alkalic oceanic magmatism can extract the essentials from a two-page abstract and an outlined summary chapter. Technically, the book has readable writ-

(SiO 2 4 5 - 66 wt.%; K20 0 . 6 - 7.2%) of ankaramites, alkalic basalts, tristanites, and

ing style, rare typos, and is logically organized. Weak points are few and include not having an introductory regional map that

trachytes (plus gabbroic xenoliths) has intrigued and occupied Imsland for over ten years. During that time, Imsland examined

places Jan Mayen into the North Atlantic geographic perspective, some variation diagrams that are not immediately clear in pur-

300 samples and acquired nearly 100 whole-rock analyses and 1200 microprobe analyses. The essence of his report, then, is

pose, and pre-1980 references. I recommend this book for every research library and for the shelves of petrologists interested in

petrography (with ample photomicrographs), major- and trace-element (Rb, Sr, Zr, Y, Cr, V, Ni, Co, Cu, Zn) compositions attended by MgO variations diagrams, and a wealth of tables and figures depicting mineral and glass compositions. Readers will not find discussions of mantle source-areas, isotope ratios, or rare-earth element patterns, but instead will discover a general resource for mineral chemistry and fractional crystallization in volcanic rocks

volcanic rocks. R.V. Fodor, Raleigh, N.C.

SEDIMENTOLOGY B. Greenwood and R.A. Davis, Jr. (Editors), 1984. Hydrodynamics and Sedimentation in Wave-Dominated Coastal Environments. De-