National Geographic : 1949 Nov
© National Geographic Society 620 Kodachrome byRobert F.Sisson Swords into Plowshares: Surplus Navy TNT Is Loaded on Atlantis at Woods Hole for Exploring the Sea Floor with Sound Waves When small blasts were set off in the water, echoes indicated the bottom sediments varied from 100 to thousands offeet thick. Larger 55-pound charges were exploded some 20 miles from the ship in refraction experiments. The sound went down to the bedrock, traveled horizontallythrough it,and finally came uptothehydrophone. From studies made of measurements of the sound speed through the basement rock, geologists infer that this part of the Atlantic Basin may never have been acontinent.