Published by the American Geophysical Union as part of the Geophysical Monograph Series, Volume 20.

The papers in this monograph are based on research contributions presented at the Symposium on "the Nature and Physical Properties of the Earth's Crust" held August 2 to 6, 1976, at Vail, Colorado. This symposium was cosponsored by the Office of Naval Research (ONR) and the Colorado School of Mines.

The year 1976 seemed to be a good one in which to hold this symposium. It is memorable as the two-hundredth anniversary of the independence of the United States of America. By coincidence, it was also the fiftieth anniversary of the Department of Geophysics of the Colorado School of Mines and the thirtieth anniversary of the Office of Naval Research.