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Tuscarora Expedition
Kelvin) sounding machine who had experimented with it on board of his
yacht. These soundings were made for the proposed telegraph cable route
between the USA and Japan. Off Japan they found no bottom at 4643 fathoms,
the Challenger nearby had sounded 4475 fathoms. Such depths were later
found to be confined to narrow zones near island arcs: deep-sea trenches in
the theory of plate tectonics later explained as subduction zones.