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Theory of Metasomatic Zoning

sum (e.g. percentages). This is a perennial problem, which particularly faces petrographers concerned with modal proportions of minerals in rocks and geochemists preoccupied with chemical analyses of minerals and rocks, and both when they try to relate mineral compositions and proportions to rock compositions. Although this is a book based on lectures given to students in two university geology departments and claimed to be written for students, the mathematics will certainly confound most students of geology--and their teachers also. It is most abstrusely written from the very first paragraph where r and p are introduced without any definition or explanation (also ~ on p. 8, 8 on p. 9, and C on p. I I). Clearly a sound knowledge of elementary statistics is assumed. If the author had made explicit reference to more actual petrological or chemical situations in deriving his general equations, the significance of the conclusions--which are not very many or positive--would have been more readily apparent. As it is, the reader is generally left to imagine a geological problem to which the discussion could be applied. The whole text only cites eight examples of petrochemical problems and although some of the suggested exercises are some help, as a teaching manual it fails dismally. A final chapter summarizing the conclusions and suggesting where petrologists now stand could have been particularly helpful. Most surprisingly, no reference is made to the work of Vistelius or even Miesch (particularly A. T. Miesch 'The constant sum problem in geochemistry' in Computer Applications in the Earth Sciences, Plenum Press, z969) and although Chayes has tried to answer Miesch's criticisms of the Chayes-Kruskal test elsewhere, the main criticism by Miesch appears to be valid. This book may help us to rationalize our delusions and realise the assumptions and uncertainties inherent in many commonly accepted procedures but it gives us little to use in the place of these procedures. I acknowledge helpful comments from Drs. Atkinson and Howarth. BERNARD E. LEAKE