Our knowledge of the oceans a hundred years ago was confined（限制） to the two-dimensional（空间的） shape of the sea surface, and the hazards（冒险） of navigation（航行） presented by the irregularities（不规则） in depth of the shallow water close to the land. The open sea was deep and mysterious（神秘的）, and anyone who gave more than a passing thought to the bottom confines of the oceans probably assumed（假定） that the sea bed was flat. Sir James Clark Ross had obtained（获得） a sounding of over 2,400 fathoms（英寻） in 1839, but it was not until 1869 when HMS Porcupine（[动]豪猪） was put at the disposal（丢掉） of the Royal Society for several cruises（巡航） that a series of deep soundings was obtained（获得） in the Atlantic, and the first samples were collected by dredging（（用挖泥船等）疏浚） the bottom. Shortly（立刻） after this, the famous HMS Challenger（ 挑战者） expedition established（建立） the study of the sea floor as a subject worthy of the most qualified physicists and geologists.