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In Death Valley, California, one of the hottest, most arid places in North America, there is much salt, and salt can damage rocks impressively. Inhabitants of areas elsewhere, where streets and highways are salted to control ice, are familiar with the resulting rust and deterioration on cars. That attests to the chemically corrosive nature of salt, but it is not the way salt destroys rocks. Salt breaks rocks apart principally by a process called crystal prying and wedging. This happens not by soaking the rocks in salt water, but by moistening their bottoms with salt water. Such conditions exist in many areas along the eastern edge of central Death Valley. There, salty water rises from the groundwater table by capillary action through tiny spaces in sediment until it reaches the surface. Most stones have capillary passages that suck salt water from the wet ground. Death Valley provides an ultra-dry atmosphere and high daily temperatures, which promote evaporation and the formation of salt crystals along the cracks or other openings within stones. These crystals grow as long as salt water is available. Like tree roots breaking up a sidewalk, the growing crystals exert pressure on the rock and eventually pry the rock apart along planes of weakness, such as banding in metamorphic rocks, bedding in sedimentary rocks, or preexisting or incipient fractions, and along boundaries between individual mineral crystals or grains. Besides crystal growth, the expansion of halite crystals (the same as everyday table salt) by heating and of sulfates and similar salts by hydration can contribute additional stresses. A rock durable enough to have withstood natural condition for a very long time in other areas could probably be shattered into small pieces by salt weathering within a few generations. The dominant salt in Death Valley is halite, or sodium chloride, but other salts, mostly carbonates and sulfates, also cause prying and wedging, as does ordinary ice. Weathering by a variety of salts, though often subtle, is a worldwide phenomenon. Not restricted to arid regions, intense salt weathering occurs mostly in salt-rich places like the seashore, near the large saline lakes in the Dry Valleys of Antarctica, and in desert sections of Australia, New Zealand, and central Asia. What is the passage mainly about?

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CROCODILE FARMS When Andy Johnson set up Britain’s first ever crocodile farm in 2006, he (1)_____ under fierce criticism from animal rights groups, opposed to the factory farming of wildlife. However, Johnson, who also farms cattle, pigs and lambs, (2)_____ that his motivation for starting a crocodile farm was for (3)_____ environmental reasons. He wants to protect wild crocodiles from being poached, and he is primarily interested in their meat, not their skins. ‘By supplying Europeans with home-produced crocodile, we can (4)_____ the market value of illegally supplied crocodile meat,’ he claims. Johnson says the meat ‘has a mild flavour – it’s low fat, high protein, very healthy and humanely produced’. His crocodiles are housed in a tropically heated room that (5)_____ around 20 by 30 metres, so they have plenty of room. However, Dr Clifford Warwick, a reptile biologist, (6)_____ concern: ‘Their biology and behaviour do not (7)_____ themselves to a captive life. The animals may seem peaceful and relaxed, but an animal behaviourist can see that they are stressed.’ In the last century, many species of crocodiles were hunted to the (8)_____ of extinction as trade in their skins flourished. Some 300,000 Australian saltwater crocodiles were killed between 1945 and 1972. The alligator suffered a similar (9)_____, although both species are now protected and their (10)_____ are slowly rising. Worldwide, the legal trade in crocodilian skins (crocodiles, alligators and caymans) has roughly tripled since 1977, risking to a million or (11)_____ animals by 2002. The majority of these are farmed animals, but upwards of 90,000 are killed annually in the (15)_____.

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