Exploring the sea-floor
原文
Lesson 30
Exploring the sea-floor
How did people probably imagine the sea-floor before it was investigated?
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.
译文
第30课
探索海底世界
在人们开始对海底进行探索之前，他们可能是如何想象海底的样子的呢？
一百年前，我们对海洋的了解仅限于海面的二维形态。
以及由于靠近陆地的浅水区水深不均匀所带来的航行危险。
广阔的海洋深邃而神秘。
任何稍微思考过海洋底部情况的人，很可能都认为海床是平坦的。
詹姆斯·克拉克·罗斯爵士在1839年测得水深超过了2,400英寻（约4,267米）。
但直到 1869 年，“H.M.S. Porcupine”号才被交由皇家学会使用，用于多次科学考察航行。
在大西洋进行了一系列深海探测，并通过挖掘海底的方式采集到了首批样本。
不久之后，著名的H.M.S.挑战者号探险队开始了对海底的研究工作。
一个值得最顶尖物理学家和地质学家研究的课题。
与铺设海底电缆相关的一系列活动迅速展开。
很快证实了挑战者的观察结果：海洋的许多区域深度在两到三英里之间。
以及水下存在一些规模相当大的地质结构（或地貌特征）。
如今，我们已经收集到了足够多的数据，可以绘制出大西洋的海底地形图（即“海底 relief map”）。
我们对海底地形的多样性也有所了解。
由于海洋覆盖了地球表面的大部分区域，
将海底视为地球地壳的基本构成部分，这是完全合理的。
大陆叠加其上，
连同海洋中的岛屿以及其他地形特征一起。
这些大陆形成了崎岖的高原地带，其海拔高度几乎达到了开放海域底部的三英里（约4.8公里）。
从海岸线开始，延伸到距离海岸几英里到几百英里的范围内……
沿着大陆架的平缓坡度延伸；从地质学角度来看，大陆架属于大陆的一部分。
实际上，大陆与海洋之间的分界线位于一个更陡峭的斜坡的底部。
这个大陆坡通常始于水深约100英寻（约183米）的位置。
在延伸数百英里后，它最终抵达真正的海底，那里的水深为2,500至3,500英寻（约4,572至6,400米）。
坡度的平均比例约为1:30（即每水平延伸30单位，垂直下降1单位），但其中也包含陡峭的、
可能是垂直的悬崖，以及被松软沉积物覆盖的缓坡地形。
在其下端附近，有一段逐渐变缓的延伸带，这几乎可以肯定是
这些物质是从大陆上被侵蚀后，被输送到深水区的。