Coated grains have always attracted attention, at first of naturalists, and later of geologists, and the interest in these peculiar bodies was re lated both to their intriguing form and their significance in facies inter pretation and sedimentology and to their relevance to accumulations of hydrocarbons and other mineral deposits. This resulted in numerous publications on this subject, and the intention of this volume is to sum marize the present state of knowledge on coated grains. The idea of the book was to unite some general papers with papers reporting case studies of both recent and ancient coated grains. The organization of the book follows this intention. The papers presented in this volume have been invited by the editor; the theme of the book merits a few words of personal history. The development of studies of coated grains during the last two decades has not only resulted in a great increase in knowledge of recent and ancient environments of coated grain formation, but also numerous important and controversial questions of classification, environmental significance, mineralogical composition etc. of ancient coated grains have arisen. To answer these questions, in 1978 I started the study of many ancient and recent occurrences of coated grains at the Institut fUr Geologie, Ruhr-UniversiUH Bochum, following the invitation of Hans Fiichtbauer and sponsored by the Alexander von Humboldt-Stiftung.

Carbonate rocks (limestones and dolomites) constitute a major partof the geological column and contain not only 60% of the world'sknown hydrocarbons but also host extensive mineral deposits. Thisbook represents the first major review of carbonate sedimentologysince the mid 1970's. It is aimed at the advanced undergraduate -postgraduate level and will also be of major interest to geologistsworking in the oil industry. Carbonate Sedimentology is designed to take the readerfrom the basic aspects of limestone recognition and classificationthrough to an appreciation of the most recent developments such aslarge scale facies modelling and isotope geochemistry. Novelaspects of the book include a detailed review of carbonatemineralogy, non-marine carbonate depositional environments and anin-depth look at carbonate deposition and diagenesis throughgeologic time. In addition, the reviews of individual depositionalsystems stress a process-based approach rather than one centered onsimple comparative sedimentology. The unique quality of this bookis that it contains integrated reviews of carbonate sedimentologyand diagenesis, within one volume.

Light scattering and absorption by small homogeneous particles can be worked-out exactly for spheres and infinite cylinders. Homogeneous particles of irregular shapes, when averaged with respect to rotation, have effects that can in general be well-approximated by reference to results for these two idealised cases. Likewise, small inhomogeneous particles have effects similar to homogeneous particles of the same average refractive index. Thus most problems can be solved to a satisfactory approximation by reference to the exact solutions for spheres and cylinders, which are fully stated here in the early part of the book. The sum of scattering and absorption, the extinction, is too large to be explained by inorganic materials, provided element abundances in the interstellar medium are not appreciably greater than solar, H 0 and NH3 being essentially excluded in the 2 general medium, otherwise very strong absorptions near 3p,m would be observed which they are not. A well-marked extinction maximum in the ultraviolet near 2200A has also not been explained satisfactorily by inorganic materials. Accurately formed graphite spheres with radii close to O.02p,m could conceivably provide an explanation of this ultraviolet feature but no convincing laboratory preparation of such spheres has ever been achieved.