Lesson 30 Exploring the sea-floor海底勘探
First listen and then answer the following question.聽錄音，然后回答以下問題。
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 bad was flat. Sir James Clark Ross had obtained a sounding of over 2,400 fathoms in 1839, but it was not until 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 there miles deep, and the existence of underwater features of considerable magnitude.
100年前，我們只知道海洋是二維平面形的，以及靠近陸地淺水區的深淺不一能給航行帶來危險。無邊無際的海洋深邃而又神秘，凡是稍稍想過大海海底的人大概 都會認為海底是平坦的。1839年，詹姆斯.克拉克.羅斯爵士曾測得海水深度超過2，400英尋；但直到1869年，皇家學會用英國“豪豬”號艦艇進行了 幾次巡航后，才在大西洋測得一個海水深度，同時能過挖掘海底，取得了研究海底的首批樣品。此后不久，英國著名的“挑戰者”號艦艇對海底的那次考察，把對海 床的研究確立為一個值得一流物理學家和地質學家從事的研究課題，鋪設海底電纜的熱潮很快證實了“挑戰者”號的觀察結果：海洋中很多地方可深達兩三英里，水 下特征差異極大。
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 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 a steeper slope.
現在已有足夠的水深測量數據來繪制一張大西洋洋底地形圖，而且我對海底地形的千變萬化也有了一定的了解。既然海洋覆蓋著地球的大部分表面，因此完全有理由 把海床看作地殼的基本模殼，上面附加著大陸以及島嶼和海洋的其他形態。大陸是崎嶇不平的高地，高出遼闊的海洋海底近三英里。從海岸線向大海延伸幾英里到幾 百英里的區域是大陸架慢坡，從地質學上來說，它是大陸的一部分。大陸和海洋的真正分界線是在陡破腳下。
This continental slope usually starts at a place somewhere near the 100-fatheom 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.
大陸架慢坡一般是從差不多100英尋水深的地方開始的，一直延伸到幾百英里遠深達2，500至3，500的地方，那里才是真正的海底。坡度平均約為 1/30，但其中包括陡峭的、乃至垂直的峭壁和沉積物覆蓋的緩和的階梯地帶，在這個地帶的低處是很長的一段尾沙地段，基本上可以斷定這個地段是大陸塊體上 侵蝕下來的物質被水沖到深水處形成的。
New words and expressions 生詞和短語
navigation
n. 航海
sounding
n. 水深度
fathom
n. 尋（1尋等于1.8米）
porcupine
n. 箭豬
dredge
v. 挖掘
expedition
n. 遠征
physicist
n. 物理學家
magnitude
n. 很多
topography
n. 地形
crust
n. 地殼
rugged
adj.崎嶇不平
tableland
n. 高地
sediment
n. 沉淀物
terrace
n. 階地
erode
v. 侵蝕
Notes on the text課文注釋
1 be confined to , 僅限于...
2 shallow water , 淺水區。
3 open sea , 無邊際的大海。
4 gave more than a passing thought to, 稍微想過。
5 H.M.S是 Her Majesty's Ship(英國船艦)的縮略形
6 at the disposal of,交由...支配。
7 a relief map, 地形圖。
8 with, superimposed upon it,the continents , togetier with the islands and other features of the oceans,這是with 引導的一個過去分詞獨立主格結構。因邏輯主語太長，所以使用了倒裝語序。superimposed upon it是邏輯謂語部分。
9 continental shelf,大陸架。
10 1 in 30 ， 1/30
Lesson 30 課后練習和答案Exercises and Answer
