1 The content ofthis article is based on a German book version ) which appeared at the end of the year 1986. The author tried to incorporate - as far as possible - new important results published in the last year. But the literature in the field of "convection and inhomogeneities in crystal growth from the melt" has increased so much in the meantime that the reader and the collegues should make allowance for any incompleteness, also in the case that their important contributions have not been cited. This could for example hold for problems related to the Czochralski growth. But especially for this topic the reader may be refered to the forthcoming volume of this series, which contains special contributions on "Surface Tension Driven Flow in Crystal Growth Melts" by D. Schwabe and on "Convection in Czochralski Melts" by M. Mihelcic, W. Uelhoff, H. Wenzl and K. Wingerath. The preparation of this manuscript has been supported by several women whose help is gratefully acknowledged by the autor: Mrs. Gisela Neuner for the type writing, Mrs. Abigail Sanders, Mrs. Fiona Eels and especially Prof. Nancy Haegel for their help in questions of the English language and Mrs. Christa Weber for reading corrections. Also the good cooperation with the Springer Verlag, especially Mrs. Bohlen and with the managing editor of Crystals, Prof. H. C. Freyhardt, who critically read the manuscript, is acknowledged.

The first edition of this book was published in 1965 and its French translation in 1966. The revised second edition followed in 1967 and its Russian translation became available in 1969. Since then, many new petrographic observations and experimental data elucidat- ing reactions in metamorphic rocks have made a new approach in the study of metamorphic transformation desirable and possible. It is felt that this new approach, attempted in this book, leads to a better unders- tanding of rock metamorphism. The concept of metamorphic facies and subfacies considers asso- ciations of mineral assemblages from diverse bulk compositions as characteristic of a certain pressure-temperature range. As new petrographic observations accumulated, it became increasingly difficult to accommodate this information within a manageable framework of metamorphic facies and subfacies. Instead, it turned out that mineral assemblages due to reactions in common rocks of a particular composi- tion provide suitable indicators of metamorphic conditions. Metamorphic zones, defined on the basis of mineral reactions, very effectively display the evolution of metamorphic rocks. Thus the im- portance of reactions in metamorphic rocks is emphasized. Experimen- tal calibration of mineral reactions makes it possible to distinguish reac- tions which are of petrogenetic significance from those which are not. This distinction provides guidance in petrographic investigations un- dertaken with the object of deducing the physical conditions of metamorphism.

This book introduces aqueous geochemistry applied to geothermal systems. It is specifically designed for readers first entering into the world of geothermal energy from a variety of scientific and engineering backgrounds, and consequently is not intended to be the last word on geothermal chemistry. Instead it is intended to provide readers with sufficient background knowledge to permit them to subsequently understand more complex texts and scientific papers on geothermal energy. The book is structured into two parts. The first explains how geothermal fluids and their associated chemistry evolve, and shows how the chemistry of these fluids can be used to, deduce information about the resource. The second part concentrates on survey techniques explaining how these should be performed and the procedures which need to be adopted to ensure reliable sampling and analytical data are obtained. A geothermal system requires a heat source and a fluid which transfers the heat towards the surface. The fluid could be molten rock (magma) or water. This book concentrates on the chemistry of the water, or hydrothermal, systems. Consequently, magma-energy systems are not considered. Hot-dry rock (HDR) systems are similarly outside the scope of this text, principally because they contain no indigenous fluid for study. Both magma-energy and HDR systems have potential as energy sources but await technological developments before they can be exploited commercially. Geothermal systems based on water, however, are proven energy resources which have been successfully developed throughout the world.

Water is the most effective agent in the climate system to modulate energy transfer by radiative processes, through its exchanges of latent heat and within cascades of chemical processes. It is the source of all life on earth, and once convective clouds are formed, it enables large vertical transports of momentum, heat and various atmospheric constituents up to levels above the tropical tropopause. Water triggers very complex processes at the earth's continental surfaces and within the oceans. At last, water in its gaseous phase is the most important greenhouse-gas! Numerical modelling and measurements of the state of the present climate system needs a very thorough understanding of all these processes and their various interactions and forcings. This is a prerequisite for more substantial forecasts of future states in all scales of time, from days to centuries. Therefore, the management of the World Climate Research Programme established in 1988 the new programme GEWEX (Global Energy and Water Cycle Experiment). GEWEX is specifically defined to determine the energy and water transports in the fast components of the climate system with the presently available modelling and measurement means and to provide new capabilities for the future. Research in GEWEX must further develop methods to determine the influence of climatic anomalies on available water resources.

Nowadays, major environmental issues are the object of large public debates de- spite the fact that scientific knowledge is often insufficient to draw unequivocal conclusions. Such is the case in the ongoing debate regarding the specific contri- butions of anthropogenic greenhouse gas emissions and of natural climate changes to global warming. At least 10 to 20 years of additional observations will be re- quired, before we will be able to conclude, with certainty, on this subject. In the mean time, and as directed by their immediate interests, people will continue to promote contradictory opinions. The media are, in part, responsible for perpetuat- ing such debates in that they convey indiscriminately the opinion of highly credi- ble scientists as that of dogmatic researchers, the latter, unfortunately too often expressing working hypotheses as established facts. Naturally, in a similarly mis- informed manner, pressure groups tend to support the researcher whose opinions most closely represent either their particular ideological battles or their economic interests and, hence, in their own way, add further to the confusion and obscurity of the debate. Only a few years ago, mercury (Hg)contamination in hydroelectric reservoirs was the object of such media and social biases. At the time, analytical data used to support the discourse were themselves uncertain and numerous hypotheses, often times fanciful, were proposed and hastily "delivered" to the public.

One of the most fundamental discoveries of the solar system was the detection of four moons in orbit around Jupiter by Galileo Galilei in 1610. The discovery was significant not only in the context of Jupiter; it gave credence to and was instrumental in firmly establishing the heliocentric system of Nicolaus Copernicus. Almost four centuries after Galileo's discovery, exten sive observations by the two Voyager spacecrafts have once again revolu tionized our thinking about the major planets, their composition, structure, origin, and evolution. This book is an attempt at summarizing our present understanding of the atmospheres and ionospheres in the outer solar system, with particular emphasis on the relevant physics and chemistry. I was motivat ed to prepare this manuscript for the following reasons. First, after under going rapid expansion in the recent past, the subject has finally attained suf ficient maturity to warrant a monograph of its own. Second, I have felt that as a result of recent observations, new and challenging problems have arisen whose resolution requires unconventional analysis and theoretical interpreta tion of existing data, as well as the collection of new kinds of data. I believe the time is ripe to put these issues in the appropriate scientific perspective, with the hope of stimulating novel theoretical, observational, and laboratory studies. I have highlighted the significant scientific problems throughout the book, especially at the end of each chapter.

turning points that, in the course of a few years, have made this The uranium minerals that today are at the centre of worldwide metal an essential raw material. attention were unknown until 1780, when Wagsfort found a First, the destructive property of fission reactions made uranium a metal of fundamental strategic importance, increas pitchblende sample in 10hanngeorgenstadt. This discovery passed unnoticed, however, since Wags fort thought that it ing research in some nations, but the revolution came with the plan for the real possibility of utilizing chain reactions for contained a black species of a zinc mineral-hence the n' lme 'pitchblende' (= pitch-like blende). Seven years later, Klaproth, energy production in place of conventional fuels. while examining the mineral, noted that it contained an oxide Since that time a 'uranium race' has been in progress in many countries-often justified by the well-founded hope of of an unknown metal, which he called 'uranium' in honour of the planet Uranus, recently discovered by Herschel. Klaproth becoming self-sufficient with regard to energy, or at least of also believed that he had separated the metal, but, in fact, the paying off a part of the financial deficit due to increasing fuel imports."

This book originally appeared in German in 1974, under the title "Bergschadenkunde" (mining subsidence engineering), and then in Russian in 1978, published by Nedra of Moscow. When the German edition was almost out of print, Springer-Verlag decided to bring out a new edition, this time in English. For this English version the text has been thoroughly revised, enlarged, and sup plemented by over 100 new figures. The book deals with the current state of international knowl edge on strata and ground movement over mine workings, with its damaging effects on mine shafts and the land surface, and with measures for regulating mining damage in law and reducing it in practice. Discussion begins with the mine excavation underground - the cause - and ends with the damage to surface structure- the effect. Methods of roof control, including the subject of rock bursts, are not discussed, since that is a field concerned more with the safety of underground workings than with minimizing damage at the surface. Of the 500 literature references in the German edi tion, only the more important for an international readership have been retained, but no value judgement on the many pUblica tions not mentioned should be read into this. The book is principally intended as a working aid for the mine surveyor, the mining engineer, the architect, and the civil engineer. For the student and the post-graduate researcher, it of fers a summary and guide to this whole field of knowledge."

Everyone is familiar with the daily changes of air temperature. The barometer shows that these are accompanied by daily changes of mass distribution of the atmosphere, and consequently with daily motions of the air. In the tropics the daily pressure change is evident on the barographs; in temperate and higher latitudes it is not noticeable, being overwhelmed by cyclonic and anticyclonic pressure variations. There too, however, the daily change can be found by averaging the variations over many days; and the same process suffices to show that there is a still smaller lunar tide in the atmosphere, first sought by Laplace. Throughout nearly two centuries these 'tides', thermal and gravitational, have been extensively discussed in the periodical literature of science, although they are very minor phenomena at ground level. This monograph summarizes our present knowledge and theoretical under standing of them. It is more than twenty years since the appearance of the one previous monograph on them - by Wilkes - and nearly a decade since they were last comprehensively reviewed, by Siebert. The intervening years have seen many additions to our know ledge of the state of the upper atmosphere, and of the tides there, on the basis of measurements by radio, rockets and satellites.

In these days of information explosion and high-cost publishing, it is perhaps only reasonable for an author to convince the reading public that it is getting something worth reading. After all, intense research into the upper mantle over the past two decades has already resulted in a number of volumes on kim berlites and their xenoliths. So why yet another one? First, in this book I have concentrated on kimberlite as an individual rock-type and a sampler of the upper mantle, in the hope of complementing such monographs as Deep seated inclusions in kimberlites and the problem of the composition of the upper mantle by N. V. Sobolev and Geologie du Diamant by M. G. Bardet, which have concentrated more on specific aspects of kimberlite and upper mantle geology; as a result I have not attempted to describe diamond prospecting and mining and, although I have attempted to give some of the up-to-date views on xenolith petrology, the confines of space have not permitted me to explore the complexities of the upper mantle as deeply as has Sobolev. Second, the literature is vast and I have tried to pull together for the reader the wide range of views and infor mation presented both in the recent geological literature and in recent multi-author volumes such as the Proceedings Vol umes of the two International Conferences on Kimberlite held at Capetown in 1973 and Santa Fe in 1977."

Papers presented at a Symposium held in Utrecht, The Netherlands, October 1982

The present book is devoted to the study of the deep Earth's interior structure, one of the most important problems of Earth sciences today. The drilling of the Kola superdeep well inaugurated a new stage in the study of the Precambrian continental crust. The well was sunk in the northeastern part of the Baltic Shield, in an area where the Precambrian ore-bearing structures, typical of the ancient platform basements, are in juxtaposition with each other. To the present the well has been drilled to a depth of 12 km, has traversed the full thickness of the Proterozoic complex and a considerable part of the Archean stratum, and is still be ing worked on. This book reviews the principal results of investigations to a depth of 11,600 m; these are described in three sections: geology, geophysics, and drilling. The book begins with a general review of the history, the present state of knowledge, and trends of further investigations in the field of study of the Earth's interior and superdeep drilling. The first section of the book considers the geology of the vicinity of the Kola superdeep well and describes its geological section based on a detailed examination both of the cores and the near-borehole area."

At first glance it may seem presumptuous to want to add yet another to the numerous books on Differential Thermal Analysis (DT A). Thermoanalytical methods have been in use for some time, as shown by the more than five thousand publications containing DT A or TG curves listed by SMOTHERS and CHIANG in the bibliography to their handbook and abstracted in the several volumes of Thermal Analysis Abstracts (TAA), edited by J. P. REDFERN for the International Con federation for Thermal Analysis (ICT A). Every three years the proceed ings of ICT A meetings are published, bringing the latest results of thermoanalytic research. There is also the Scifax DT A Data Index, edited by R. C. MACKENZIE (1962) and modeled on the ASTM pattern card index (used for X-ray investigations), a compilation of the DT A data for several hundred minerals, and inorganic and organic materials. The theoretical foundations of thermogravimetry and DT A have been described in detail by LEHMANN, DAS and PAETSCH (1953), R. C. MACKENZIE (1957, 1970), DUVAL (1963), WENDLANDT (1964), GARN (1965), F. PAULIK et al. (1966), SMOTHERS and CHIANG (1966), and KEATTCH (1969). Thermoanalytical results are strongly influenced by various factors relative to preparation and equipment (see 1-2. 4 of this study). This is the reason why we frequently find, in these books as well as in the Scifax-Card catalog, contradictory data on the same substance."

In its relentless pursuit of further knowledge, science tends to compartmentalize. Over the years the pursuit of What might be called geophysical acoustics of the sea-surface has languished. This has occured even through there are well-developed and active research programs in underwater acoustics, ocean hydrodynamics, cloud and precipitation physics, and ice mechanics - to name a few - as well as a history of engineering expertise built on these scientific fields. It remained to create a convergence, a dialogue across disciplines, of mutual benefit. The central theme of the Lerici workshop, perhaps overly simplified, was 'What are the mechanisms causing ambient noise at the upper surface of the ocean?' What could hydrodynamicists contribute to a better understanding of breaking wave dynamics, bubble production, ocean wave dynamics, or near-surface turbulence for the benefit of the underwater acoustics community? What further insights could fluid dynamicists gain by including acoustic measurements in their repertoire of instrumentation? While every attendee will have his or her percep tions of details, it was universally agreed that a valuable step had been taken to bring together two mature disciplines and that significant co-operative studies would undoubtedly follow. The scope of the workshop was enlarged beyond its original intent to also include the question of ice-noise generation. The success of this decision can be seen in high quality of the presentations. the contribution of its disciples in the other workshop discussions and the heightened awareness and interest of we other novices."

Basic magmatic rocks make up approximately three-quarters of the crust ofthe present day Earth. Because we can observe and study the volcanic products of present day tectonic regimes comprehensively, we can shed light on ancient tectono-magmatic provinces, and thereby deduce the petrogenesis and evolution of the oldest basic rocks. This is the primary objective of this book. The book was conceived in order to provide a comprehensive review of the basic rocks produced during the first half of the Precambrian, i.e. the Archaean and early Proterozoic, to about 1.8 Ga years ago. Two major questions are addressed. First, what basic magmas were generated during the early Precambrian: were these magmas globally uniform, and to what extent were prevailing tectonic controls and compo sitions analogous to those of the present day? Clearly, this can be answered only by bringing together fundamental information about all relevant basic magmatic events. Second, is there any systematic temporal variation in the nature of basic suites, and what implications might such variations have on our interpretations of early Earth history? Are there important differences between early Archaean, late Archaean, Proterozoic and modern basic magmatic suites? The book uses two approaches to address these questions. Early chapters examine the fundamental characteristics of these basic rocks, whilst later chapters assess regional distribution and development by providing an overview of each major early Precambrian craton."

On February 19, 1973, five centuries have elapsed since the birth of Nicolaus Coperni cus - the greatest astronomer of the Renaissance period - who rediscovered for us the heliocentric model of the solar system, and documented it by his life's work in such a manner as to make its concept a permanent property of mankind. The life of Copernicus, extending from 19 February 1473 to his death on 24 May 1543, was not too rich in adventures or biographical facts. Born in Toruti from a family of Polish burghers, he received his first university training in Cracow between 1491-1494. From Cracow he proceeded to Italy to spend the years between 1496-1503 at the Universities of Bologna, Padua and Ferrara - with occasional visits to Rom- in preparation for an ecclesiastical career. When Bishop Watzenrode - his patron and maternal uncle - could no longer extend his leave, Copernicus returned to Poland in 1503 to enter the service of the church establishment, which soon led to a canonry at the Frombork (Frauenburg) Cathedral in Warmia. And there - in the northern mists not far from the Baltic shores - in a land so different in climate from the sunny Italy of his youth - he was destined to spend the rest of his life."

The main aim of this paper is to present some new and general results, ap plicable to the the equations of two phase flow, as formulated in geothermal reservoir engineering. Two phase regions are important in many geothermal reservoirs, especially at depths of order several hundred metres, where ris ing, essentially isothermal single phase liquid first begins to boil. The fluid then continues to rise, with its temperature and pressure closely following the saturation (boiling) curve appropriate to the fluid composition. Perhaps the two most interesting theoretical aspects of the (idealised) two phase flow equations in geothermal reservoir engineering are that firstly, only one component (water) is involved; and secondly, that the densities of the two phases are so different. This has led to the approximation of ignoring capillary pressure. The main aim of this paper is to analyse some of the consequences of this assumption, especially in relation to saturation changes within a uniform porous medium. A general analytic treatment of three dimensional flow is considered. Pre viously, three dimensional modelling in geothermal reservoirs have relied on numerical simulators. In contrast, most of the past analytic work has been restricted to one dimensional examples."

The papers in this volume are dedicated to Professor Dr. Dr. h.c. G. Christian Amstutz by his colleagues, friends, and students on the occasion of his 60th anniversary. The authors of this book - the theme was restricted to syngenesis and epigenesis in the formation of mineral deposits - wish to honour with their articles a scientist who has contributed to, and substantially promoted the understanding of the genesis of mineral deposits in the last decades. The majority of the articles deal with strata-bound depos its, thus reflecting one of his main scientific interests. In the tradition of his professors, Paul Niggli and Paul Ramdohr, G.C. Amstutz has maintained an open and active interest in many fields of earth science. His numerous papers have triggered a remarkable number of new ideas and investigations in a variety of fields, and the "happy marriage" of economic geology with sedimentology is cer tainly one of his main successes, starting with the first Symposium on Sedimentology and Ore Genesis at the Sixth International Sedimentological Congress at Delft in 1963."

The problem of time-and strata-bound formation of ore deposits has during the past decade become one of the most debated topics in cur rent international discussion. Due to the amazing results of modern mineral exploration and world-wide geophysical research, the mutual relationship between the complex geological history pf a crustal seg ment and the development of distinct metallogenic provinces (ore belts) has received much interest. Reviewing the earth's history in this light one can now recognize metallogenic epochs even of global range which document the existence of world-wide time-bound ore enrich ments. The knowledge of these metallogenetic processes has been growing step by step for several decades. It began with simple observations and sceptic interpretations, which at first threw heretical spot lights on to the edifices of the prevailing theories on granitic differentiation as the favoured source of ore deposits. It was obvious that the new ideas at first referred to ore enrichments in sedimentary sequences, nowadays summarized under the term strata-bound, and mainly interpreted as stratiform or sedimentary ore deposits. Moreover, the modern term "strata-bound" also includes ore mineralizations which are bound to distinct units of layered (intrusive or extrusive) igneous complexes as a general descriptive term without genetical restriction Albert Maucher is one of the representatives of the initial era who discussed these genetical questions critically in the decade before the 2nd World War."

The second volume of this series consists of three parts. Part I focuses on the research on intracrystalline reactions. This work, which began nearly two decades ago, is critically reviewed by Ghose and Ganguly in Chapter 1. Besides the review, the authors include some of their previously unpublished work to demonstrate how future research could aid in obtaining data on thermodynamics of solid solutions and in understanding the cooling history of igneous and metamorphic rocks. The latter is also the theme adopted by Kretz in the second chapter, which examines the redistribution of Fe and Mg in coexisting silicates during cooling. Chapter 3 contains new data on Fe-Mg distribution in clinopyroxenes. Dal Negro and his co-authors have selected a series of clinopyroxenes from volcanic rocks and present site occupancy data on several clinopyroxenes of intermediate compositions. The data set has not been published before and is the first of its kind. Part II of this book begins with a chapter on melts by Gaskell, who explores the relationship between density and structure of silicate melts. This is followed by the synthesis of data generated in the U.S.S.R. by Shmulovich and his co-authors on fluids. Blencoe, Merkel and Seil present a thorough analysis of the phase equilibrium data on feldspars coexisting with fluids in the third chapter in this part.

The Advanced Science Institute on which this publication is based took the somewhat unusual form of a geological field symposium held during late August 1984. It was designed to demonstrate to experienced earth scientists from the North Atlantic area the full range of geological phenomena encountered in the British Caledonian rocks. The ASl travelled from South Wales to the far northwest of Scotland by the route shown on the map and in doing so examined sedimentary, igneous and metamorphic rocks from Pembrokeshire (Dyfed), Cardigan (Ceridigian), Snowdonia, Anglesey, the English Lake District and the Southern Uplands and Highlands of Scotland. Thus the fifty or so participants in the ASl studied the geological history and major structures of rocks exposed on either side of the supposed Lower Palaeozoic Iapetus Ocean the British sector of which closed to the south of the present Southern Uplands. Wales (1-5) afforded insight into the nature of the late Precambrian basement of England and Wales and the relationship of sedimentary and volcanic cover sequences to this basement. The Ordovician sequence in Wales is a sample of the volcanic rocks typical of a marginal basin, and were examined in Pembrokeshire and Snowdonia. The English Lake District (6) displays rocks from an island arc also of Ordovician age.

1.1. HISTORICAL DEVELOPMENT OF THE OPHIOLITE CONCEPT. Ophiolite, Greek for 'the snake stone', appears to have received its first written definition by Brongniart (1813) as a serpentine matrix containing various minerals. Later in 1821 and 1827, Brongniart determined that volcanic and gabbroic rocks were also present, associated with cherts, and he ascribed an igneous origin to the ophiolite. Amstutz (1980) gives an excellent exegesis of these early contributions and traces the further use of the term and concept of ophiolite. This concept had been forged in the western Alps and Apennines where, thanks to talented Italian geologists, in particular A. Sismonda, B. Gastaldi, V. Novarese and S. Franchi, the study on metamorphic ophiolites (the 'pietre verdi') has rapidly progressed. At the tum of the century the association of radiolarite, diabase, gabbro (euphotide), and serpentinite-peridotite was clearly identified, even through their metamorphic transformations. In 1902, Franchi developed the hypothesis introduced earlier by Lotti (1886), of a submarine outflow to explain the 'pietre verdi' association, on the basis of the attribution of the variolites and metamorphic prasinites to an hypabyssal volcanism, also responsible for the formation of radiolarites. Thus, before the popular work of Steinmann in 1927, the various components constituting an ophiolite had been identified and its hypabyssal origin proposed. As recalled by Amstutz (1980), the so-called 'Steinmann trinity', which consists of the association of radiolarites, diabases and serpentinites, was more completely and better defined in these earlier works.

work on structural and stratigraphic relationships is presented from various parts of the mountain belt. In the first paper of the section, R. O. Greiling (Heidelberg) describes the Middle Allochthon of Vasterbotten, northern Sweden, where tectonic windows through the Upper Allochthon (Seve Nappe) show that the Middle Allochthon has a similar lithostratigraphy to that of the Stalon Nappe Complex of the eastern Caledonian margin but with a more ductile deformation and metamorphosed to a higher grade following thrust emplacement. These relations are explained by suggesting that the window rocks were initially subducted beneath a colliding western plate but were later accreted to the base of the western plate and thrust with it. The thrust geometry of the windows, described as antiformal stacks, agrees with this model. The Middle Allochthon of the Caledonian margin in northern Sweden is described by R. O. Greiling and R. Kumpulainen (Heidelberg and Stockholm) who record two distinct metasedimentary units separated by a thick zone of mylonites interpreted as a lateral thrust ramp. Turbidites in the northern unit were derived from an unidentified igneous source to the east and cannot be correlated with other sequences in the Middle Allochthon. In another paper dealing with the northern Swedish Caledonides, L. Hansen (Uppsala) describes down-to-the-west normal faults cutting the autochthonous Cambrian sediments in the tunnel sections of the Vietas Hydropower Station, but themselves being truncated by the basal decollement of the Lower Allochthon.

In recent years mineralogy has developed even stronger links with solid-state chemistry and physics and these developments have been accompanied by a trend towards further quantification in the theoretical as well as the experimental aspects of the subject. The importance of solid-state chemistry to mineralogy was reflected in a symposium held at the 1982 Annual Congress of The Royal Society of Chemistry at which the original versions of most of the contributions to this book were presented. The meeting brought together chemists, geologists and mineralogists all of whom were interested in the application of modern spectroscopic techniques to the study of bonding in minerals. The interdisci plinary nature of the symposium enabled a beneficial exchange of information from the various fields and it was felt that a book presenting reviews of the key areas of the subject would be a useful addition to both the chemical and mineralogical literature. The field of study which is commonly termed the 'physics and chemistry of minerals' has itself developed very rapidly over recent years. Such rapid development has resulted in many chemists, geologists, geochemists and mineralogists being less familiar than they might wish with the techniques currently available. Central to this field is an understanding of chemical bonding or 'electronic structure' in minerals which has been developed both theoretically and by the use of spectroscopic techniques."

The fourth volume in this series consists of eleven chapters. The first five deal with more theoretical aspects of the kinetics and mechanisms of meta morphic reactions, and the next six consider the interdependence of defor mation and metamorphism. All papers deal with natural processes that inter act on various time scales and with different degrees of mass and heat transfer. Consequently, many fundamental axioms of metamorphic petrol ogy and structural geology are questioned both for their accuracy and their usefulness. In raising such questions, most contributors have pointed to ways in which the answers could be forthcoming from appropriate experi mental studies or observations on natural materials. In their discussion of how order/disorder can influence mineral assem blages, Carpenter and Putnis emphasize that metastable crystal growth is common in metamorphic systems and state' 'there may be some reluctance (among many earth scientists) to accept that significant departures from equilibrium could occur." On the basis of presented evidence, they question whether reactions ever occur close to an equilibrium boundary. The neces sity for pressure or temperature overstepping is also required by nucleation rate theory. In any case, the degree of order is severely influenced by these kinetic effects in igneous, sedimentary, and metamorphic environments."