英國學(xué)生科學(xué)讀本 Lesson 80 我們腳下的土地(1)

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第80課 我們腳下的土地

Perhaps you have seen men digging in the earth, either preparing for the foundations of a house, or making a deep ditch or a railway cutting. If you watch them at work, you will see that the earth which they turn up is not all of the same colour.

也許你看到過這樣的場景：人們?yōu)榱藴蕚浞课莸牡鼗? 或者建造一條深溝或者鐵路而挖土。觀察他們的工作, 就會發(fā)現(xiàn), 他們挖出來的泥土顏色不盡相同。

On the top there may be grass growing, and when the men cut through the tough network of its roots, they find a loose black or dark-brown earth which is easy to dig. This is called the soil.

土地的最上層可能長有一些花草, 當人們的挖掘工具穿過這些花草強韌的根部之后, 一層松軟的黑色或深棕色泥土便露了出來。這就是土壤, 它們非常容易挖掘。

When they go a foot or two further down, they reach a kind of earth which is much lighter in colour and much harder to dig. This is called the subsoil. If they have to dig still deeper, they will come after a while to the hard and solid rock. In some places the workmen may have to dig down only a few feet before they reach the rock, but in other places both the soil and the subsoil may be many feet deep. The depth varies very much in different spots.

當人們繼續(xù)向下挖掘一至兩英尺之后就會觸碰到一種顏色較淺但很難挖掘的泥土, 它的名字叫做底土。如果還需要繼續(xù)深挖, 不久之后就能看到堅硬的固體石頭。有時候, 工人們可能只需挖掘幾英尺便能看到巖石層;不過另外一些時候, 巖石層上方的土壤與底土可能達到很多英尺之厚。在不同的地方深度相差很大。

At one time the soil was just like the subsoil, and before that it formed part of some hard and solid rock. How are the hard rocks broken up and changed into soil? Chiefly by means of water. Rain-water dissolves the rock called limestone, just as your warm tea dissolves the lumps of sugar which you put into it, though more slowly. The tops of limestone hills are often worn into the most curious shapes by the action of the rain-water.

曾幾何時, 土壤與底土一樣結(jié)實, 再往前追溯的話, 它還曾經(jīng)是堅硬、結(jié)實的巖石。如此堅硬的石頭為何會碎裂并且變成土壤呢? 主要原因就是水。雨水能夠溶解石灰?guī)r, 就像溫?zé)岬牟杷軌蛉芙馓菈K一樣, 只是前者的速度要緩慢很多。在雨水的作用下, 石灰石山的頂部會變成各種奇異的形狀。

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