30 · 海底勘探
Exploring the Sea-floor
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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. The open sea was deep and 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. Sir James Clark Ross had obtained a sounding of over 2,400 fathoms in 1839, but it was not until 1869, 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. A burst of activity associated with the laying of submarine cables soon confirmed the challenger's observation that many parts of the ocean were two to three miles deep, 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. Since the sea covers the greater part of the earth's surface, it is quite reasonable to regard the sea floor as the basic form of the crust of the earth, with, superimposed upon it, the continents, together with the islands and other features of the oceans. The continents form rugged tablelands which stand nearly three miles above the floor of the open ocean. From the shore line, out to a distance which may be anywhere from a few miles to a few hundred miles, runs the gentle slope of the continental shelf, geologically part of the continents. The real dividing line between continents and oceans occurs at the foot of a steeper slope.
This continental slope usually starts at a place somewhere near the 100-fathom mark and in the course of a few hundred miles reaches the true ocean floor at 2,500-3,500 fathoms. The slope averages about 1 in 30, but contains steep, probably vertical, cliffs, and gentle sediment-covered terraces, and near its lower reaches there is a long tailing-off which is almost certainly the result of material transported out to deep water after being eroded from the continental masses.
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整篇课文
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. The open sea was deep and 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. Sir James Clark Ross had obtained a sounding of over 2,400 fathoms in 1839, but it was not until 1869, 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. A burst of activity associated with the laying of submarine cables soon confirmed the challenger's observation that many parts of the ocean were two to three miles deep, 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. Since the sea covers the greater part of the earth's surface, it is quite reasonable to regard the sea floor as the basic form of the crust of the earth, with, superimposed upon it, the continents, together with the islands and other features of the oceans. The continents form rugged tablelands which stand nearly three miles above the floor of the open ocean. From the shore line, out to a distance which may be anywhere from a few miles to a few hundred miles, runs the gentle slope of the continental shelf, geologically part of the continents. The real dividing line between continents and oceans occurs at the foot of a steeper slope.
This continental slope usually starts at a place somewhere near the 100-fathom mark and in the course of a few hundred miles reaches the true ocean floor at 2,500-3,500 fathoms. The slope averages about 1 in 30, but contains steep, probably vertical, cliffs, and gentle sediment-covered terraces, and near its lower reaches there is a long tailing-off which is almost certainly the result of material transported out to deep water after being eroded from the continental masses.
一百年前，我们对海洋的了解，还只限于海面的平面轮廓，以及近岸浅水区深浅不一给航行带来的危险。远洋深邃而神秘，稍微认真想过海底是什么样子的人，大概都会以为那里一片平坦。詹姆斯·克拉克·罗斯爵士曾在一八三九年测得超过二千四百英寻的水深；但直到一八六九年，英国海军“豪猪”号交由皇家学会开展数次考察后，人们才在大西洋取得一系列深海测量数据，并通过海底拖捞收集到首批样本。此后不久，著名的“挑战者”号远征，确立了海底研究的学术地位，使之成为值得顶尖物理学家和地质学家投入的领域。随后，铺设海底电缆带动了一轮密集活动，很快证实了“挑战者”号的发现：海洋中许多地方深达两三英里，水下还存在规模可观的地形。
如今，已有足够的水深数据来绘制大西洋海底地形图，我们也开始了解海底地形的千姿百态。海洋覆盖了地球表面的大部分，因此，把海底视为地壳的基本形态，把大陆、岛屿和其他海洋地貌看成叠加在其上的部分，是很合理的。大陆犹如崎岖的台地，比远洋海底高出将近三英里。从海岸线向外延伸几英里到几百英里，是坡度平缓的大陆架；从地质上说，它仍是大陆的一部分。大陆与大洋真正的分界线，在更陡的一段斜坡的底部。
这段大陆坡通常从水深约一百英寻处开始，延伸数百英里后，到达二千五百至三千五百英寻深的真正洋底。它的平均坡度约为一比三十，但其间既有陡峭、甚至可能垂直的崖壁，也有覆盖着沉积物的平缓阶地。在接近坡底的地方，坡势会拖出长长的一段，逐渐趋于平缓；这几乎可以肯定，是大陆物质受侵蚀后，被输送到深水区堆积而成的。
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译文依据整理稿，由本站按中文表达重新校订；解析据吴应时整理资料及首轮审校稿；词伙与练习提示为本站学习设计。原PDF第121—125页，2022年2月第2版。