Notation on back, "In the Endless Caverns of New Market, Virginia, 90 feet below the gigantic 180,000 years old calcite 'Twin Columns' shown in the left foreground, flows an underground stream to reach which the University of Virginia scientists climbed down an 80-foot subterranean cliff by means of a stout rope, with a 50 pound Geiger-Mueller Counter strapped to the back of one of the men, to record cosmic rays on the bank of the stream after these rays from outer space had penetrated 180 feet of limestone."
