02 April 1965
Vol 148, Issue 3666

About The Cover

Pamice from the volcanic tuff of Bed I, Olduvai Gorge. The specimen was mounted in plastic, polished, and etched. The three arrows indicate the location of spontaneous fission events. Each event appears as an elliptical pit. The age of the pumice, determined by counting such events, has been found to be 2 million years (about X 700). See page 72.