Our knowledge of the oceans a hundred years ago was confined to the two-dimensional shape of the sea-surface and the hazards of navigation presented by the irregularities in depth of the shallow water close to the land. (1)_______________________. Sir James Clark Ross had obtained a sounding of over 2,400 fathoms in 1836 but it was not until 1800, when H.M.S. Porcupine was put at the disposal of the Royal Society for several cruises, that a series of deep soundings was obtained in the Atlantic and the first samples were collected by dredging the bottom.Shortly after this the famous H.M.S. Challenger expedition established the study of the sea-floor as a subject worthy of the most qualified physicists and geologists. (2)_______________________, and the existence of underwater features of considerable magnitude. Today enough soundings are available to enable a relief map of the Atlantic to be drawn and we know something of the great variety of the sea-bed's topography.
1 The open sea was deepen mysterious and anyone who gave more than a passing thought to the bottom confines of the oceans probably assumed that the sea-bed was flat.
2 A burst of activity associated with laying summering cables soon confirmed the challengers' observation that many parts of the ocean were 2-3 miles deep.
发表于 2012-1-12 10:31
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发表于 2012-1-15 13:49
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