Contents

02 May 1975
Vol 188, Issue 4187

About The Cover

Twilight illumination of the ash stratum from Tucson, Arizona, 22 November 1974, showing the heavily striated structure of the layer. Saguaro cactus is in foreground. See page 477. [Aden B. Meinel and Marjorie P. Meinel, University of Arizona, Tucson]