Cave exploration, or pot-holing, as it has come to be known, is a relatively new sport. Perhaps it is the desire for solitude or the chance of making an unexpected discovery that lures people down to the depths of the earth. It is impossible to give a satisfactory explanation for a pot-holer's motives. For him, caves have the same peculiar fascination which high mountains have for the climber. They arouse instincts which can only be dimly understood.
Exploring really deep caves is not a task for the Sunday afternoon rambler. Such undertakings require the precise planning and foresight of military operations. It can take as long as eight days to rig up rope ladders and to establish supply bases before a descent can be made into a very deep cave. Precautions of this sort are necessary, for it is impossible to foretell the exact nature of the difficulties which will confront the pot-holer. The deepest known cave in the world is the Gouffre Berger near Grenoble. It extends to a depth of 3,723 feet. This immense chasm has been formed by an underground stream which has tunneled a course through a flaw in the rocks. The entrance to the cave is on a plateau in the Dauphine Alps. As it is only six feet across, it is barely noticeable. The cave might never have been discovered has not the entrance been spotted by the distinguished French pot-holer, Berger. Since its discovery, it has become a sort of potholers' Everest. Though a number of descents have been made, much of it still remains to be explored.
A team of pot-holers recently went down the Gouffre Berger. After entering the narrow gap on the plateau, they climbed down the steep sides of the cave until they came to narrow corridor. They had to edge their way along this, sometimes wading across shallow streams, or swimming across deep pools. Suddenly they came to a waterfall which dropped into an underground lake at the bottom of the cave. They plunged into the lake, and after loading their gear on an inflatable rubber dinghy, let the current carry them to the other side. To protect themselves from the icy water, they had to wear special rubber suits. At the far end of the lake, they came to huge piles of rubble which had been washed up by the water. In this part of the cave, they could hear an insistent booming sound which they found was caused by a small waterspout shooting down into a pool from the roof of the cave. Squeezing through a cleft in the rocks, the pot-holers arrived at an enormous cavern, the size of a huge concert hall. After switching on powerful arc lights, they saw great stalagmites -- some of them over forty feet high -- rising up like tree-trunks to meet the stalactites suspended from the roof. Round about, piles of limestone glistened in all the colours of the rainbow. In the eerie silence of the cavern, the only sound that could be heard was made by water which dripped continuously from the high dome above them.
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1.Perhaps it is the desire for solitude or the chance of making an unexpected discovery that lures people down to the depths of the earth.
结构分析: it is the desir e ......or the chance ......that......，运用了强调了句式，被强调的部分是句子的主语:it is the desire ......or the chance
eg: It is the desir for knowledge that lures her into the book world. 是她对知识的渴求吸引她走进书的海洋。
2.It can take as long as eight days to rig up rope ladders and establish supply bases before a descent can be made into a very deep cave.
结构分析: before 引导时间状语从句。It 为形式主语，as long as eight days 作谓语can take 的宾语，不定式短语to ring up rope ladders and to establish supply bases作真正的主语。
ring up 草草作成 eg. Soldiers rigged up tents for the night.
make a descent 下落
3.Precautions of this sort are necessary,for it is impossible to foretell the exact nature of difficulties which will confront the pot-holer.
precaution n.预防措施 Eg: We have to save our precautions of insuring my car.
take steps/actions 采取措施
4.The cave might never been discovered had not the entrance been spotted by the distinguished French pot-holers,Berger.
结构分析：had not the entrance been spotted by the distinguished French pot-holers,Berger是非真实条件句，省略了if。即：如果条件从句中有were ,had 或should ,可以把if省略，把这几个词放到主语之前，构成主谓倒装.
eg:Had he taken a little more time to think,he might have acted more sensibly.
5.They had to edge their way along this,cometimes wading across shallow streams ,or swimming across deep pools.
结构分析：简单句，cometimes wading across shallow streams ,or swimming across deep pools做主语补足语，补充说明该洞穴内的险峻。
词汇注释：edge one's way 侧身挤过，侧身徐徐向前
6.After switching on powerful are lights ,they saw great stalamites--some of them over forty feet high--rising up like tree-trunks to meet the stalactites suspended from the roof.
结构分析：some of them over forty feet high做宾补，补充说明stalamite的高度；现在分词短语rising......roof 做宾补，补充说明stalamite的形态，不定式短语to meet......作状语，表结果，suspended form the roof作定语，修饰stalamite
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