第30课

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Our knowledge of the oceans a hundred years ago was confined to the two-dimensional shape of the sea surface

一百年前，我们对海洋的了解仅限于海面的二维形状

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and the hazards of navigation presented by the irregularities in depth of the shallow water close to the land.

以及陆地附近浅水区深度不规则所带来的航行危险。

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The open sea was deep and mysterious,

开阔的海洋深邃而神秘，

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and anyone who gave more than a passing thought to the bottom confines of the oceans probably assumed that the sea-bed was flat.

任何对海洋底部边界稍加思考的人可能都认为海床是平坦的。

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Sir James Clark Ross had obtained a sounding of over 2,400 fathoms in 1839,

詹姆斯·克拉克·罗斯爵士于1839年测得超过2400噚的深度，

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but it was not until 1869, when H.M.S. Porcupine was put at the disposal of the Royal Society for several cruises

但直到1869年，当“豪猪号”军舰被皇家学会征用进行数次航行时，

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that a series of deep soundings was obtained in the Atlantic and the first samples were collected by dredging the bottom.

才在大西洋获得了一系列深海探测数据，并通过海底拖网收集了第一批样本。

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Shortly after this the famous H.M.S. Challenger expedition established the study of the sea-floor

此后不久，著名的“挑战者号”军舰远征队确立了海底研究

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as a subject worthy of the most qualified physicists and geologists.

成为值得最合格的物理学家和地质学家研究的课题。

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A burst of activity associated with the laying of submarine cables

随之而来的海底电缆铺设热潮

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soon confirmed the Challenger's observation that many parts of the ocean were two to three miles deep,

很快证实了“挑战者号”的观测结果：海洋许多地方深达两到三英里，

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and the existence of underwater features of considerable magnitude.

并存在着规模巨大的水下特征。

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Today, enough soundings are available to enable a relief map of the Atlantic to be drawn

如今，已有的测深数据足以绘制出大西洋的浮雕地图，

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and we know something of the great variety of the sea bed's topography.

我们对海底地形的巨大多样性有了一定的了解。

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Since the sea covers the greater part of the earth's surface,

由于海洋覆盖了地球表面的大部分，

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it is quite reasonable to regard the sea floor as the basic form of the crust of the earth,

将海底视为地壳的基本形态是相当合理的，

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with superimposed upon it the continents,

大陆、

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together with the islands and other features of the oceans.

以及岛屿和海洋的其他特征都叠加其上。

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The continents form rugged tablelands which stand nearly three miles above the floor of the open ocean.

大陆形成了崎岖不平的高原，它们比开阔海洋的海底高出近三英里。

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From the shore line, out to a distance which may be anywhere from a few miles to a few hundred miles,

从海岸线向外延伸，距离可能从几英里到几百英里不等，

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runs the gentle slope of the continental shelf, geologically part of the continents.

是大陆架的平缓斜坡，它在地质学上属于大陆的一部分。

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The real dividing line between continents and oceans occurs at the foot of a steeper slope.

大陆和海洋的真正分界线出现在一个更陡峭的斜坡底部。

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This continental slope usually starts at a place somewhere near the 100-fathom mark

这个大陆坡通常始于100噚标记附近的某个地方，

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and in the course of a few hundred miles reaches the true ocean floor at 2,500-3,500 fathoms.

并在几百英里的延伸中到达2500-3500噚的真正海底。

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The slope averages about 1 in 30, but contains steep,

该斜坡平均坡度约为1:30，但包含陡峭的、

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probably vertical, cliffs, and gentle sediment-covered terraces,

可能是垂直的悬崖，以及平缓的被沉积物覆盖的阶地，

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and near its lower reaches there is a long tailing-off which is almost certainly the result of

在其下部区域，有一个长长的逐渐减缓的坡段，这几乎肯定是由于

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material transported out to deep water after being eroded from the continental masses.

物质从大陆块体被侵蚀后输送到深水区的结果。