Besides these two cavern systems, there is another system of caves located in Mexico known as the Cave of Crystals which lies far beneath the Chihuahuan Desert and currently produces large amounts of lead and silver. This cavern system is also made up of limestone; however, the crystals found in this system are unlike any found in the world, for they were formed by the action of super-heated magma which allowed some of the crystals to grow to enormous sizes, some being almost thirty-seven feet long (Palmer, 251). Unfortunately, like other cavern systems located outside of the U.S., on-going efforts are currently being made to preserve this system and others from individuals who only wish to profit from the selling of crystals on the black market.

In conclusion, it should be noted that there are other cavern systems scattered around the world, especially in Europe, which are not limestone-based; rather, they are either caves formed by wind and erosion or by ice during the last glacial period in Europe some 100,000 years ago. Thus,...

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