NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council and by competent authorities of the Israel Academy of Sciences and Humanities, the Royal Scientific Society of Jordan, and the Palestine Academy for Science and Technology. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.

This study was supported by the Casey Program Fund and the Arthur Day Program Fund of the U.S. National Research Council Fund. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the organization that provided support for this project.

Library of Congress Catalog Card Number 97-80489

International Standard Book Number 0-309-06421-X

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Cover art: Watercolor by Marc Castelli, Chestertown, Md., after photograph by David Policansky.

Copyright 1999 by the National Academy of Sciences. All rights reserved.

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