Of course such a book as we propose here is not the product of just two
people working together, although the experience has been a great
pleasure for us. We would like to thank our many collaborators and
students who have encouraged our effort by their, often, sharp
criticism. We hope that we have used their comments to good effect. Es-
cially we would like to thank Pierre Barré for his help, enthusiasm and
consent for the use of much of his thesis material in formulating the
last chapter of the book. Dominique Righi was instrumental in giving us
ideas, useful comments and vigorous debate for a great number of our
ideas and during the periods of formulation of our conclusions. Our
approach is from mineral chemistry and hence has greatly benefited from
disc- sions with people who know soils and plants. The project of this
book was realized and encouraged with the help of Wolfgang Engel who,
unfortunately is not with us to see its finalization. We greatly regret
his passing. This book is not in the general pattern of accepted
knowledge and analysis of the phenomena which affect the occurrence of
clays in the surface environment. We stress the role of plants at the
bio-interface and the importance of microsystems at the water/ rock
interface. We believe that the literature at our and anyone's disposal
shows that the system of clay formation and reaction is highly dynamic,
especially at the surface.
