海底勘探
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Exploring the Sea-floor
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第1段
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.
100年前，我们对海洋的了解，还仅限于海面的平面轮廓，以及近岸浅水区水深不均给航行带来的危险。 无边无际的远洋深邃而神秘。凡是稍稍想过大海底部是什么样子的人，大概都会认为海底是平的。1839年，詹姆斯·克拉克·罗斯爵士曾测得海水深度超过2,400英寻(1英寻等于1.828米)；但直到1869年，皇家学会用英国“豪猪”号舰艇进行了几次巡航后，才于大西洋测得一系列海水深度，同时通过挖掘，取得了首批海底样品。此后不久，英国著名的“挑战者”号舰艇的考察，把对海床的研究确立为一个值得一流物理学家和地质学家投身的学科。 铺设海底电缆的热潮很快证实了“挑战者” 号的观测结果：海洋中很多地方可深达两三英里；也证实了水下存在相当丰富的地形特征。
第2段
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.
现在充足的水深测量数据，已使得绘制一张大西洋洋底地形图成为可能。而且我们对海底地形的千姿百态也不再一无所知。 海洋覆盖着地球大部分表面，因此把海床视为地壳的基本形式相当合理：海床上叠加着大陆以及岛屿和海洋的其他形态。大陆构造的崎岖高地，比远洋海底高了将近三英里。 从海岸线向大海延伸几英里到几百英里的区域是大陆架缓坡，从地质学上分类，它仍是大陆的一部分。陡坡坡脚才是大陆和海洋的真正分界线。
第3段
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.
大陆坡通常从约100英寻深处开始，一直延伸到几百英里远，深达2,500至 3,500英寻的地方，那里才是真正的海底。平均坡度约为1∶30（约3.33%，折合约1.91°），但其中包括陡峭的、乃至垂直的峭壁和被沉积物覆盖的缓和阶梯地带。在低处所及，有一段延绵开去而逐渐消融的地带，几乎可以确定这是从大陆块体上侵蚀下来的物质被水冲往深水处形成的。
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译文与解析据吴应时整理资料及本站首轮审校稿；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。