  We have seen then in the preceding discussion how caves are formed largely in rocks saturated with water, and how by land movements and changes of sea level the caves and pores formed in this rock are moved above permanent water levels and exposed to air. It then becomes possible to deposit rock in the pores and caves rather than to increase their size by solution. As you go through the caves you will notice that the walls are wet and that water is oozing out of the pores of the rock. This water has just passed through limestone and has dissolved parts of the rock. The reader undoubtedly knows that water will dissolve a substance in large quantities and more rapidly if it is hot, and that it can hold more gases to make stronger acids if it is under pressure. So, having been released from a relatively warm rock in which it was under some pressure and where there was little air circulating, into a large cave where rapidly circulating air cools the cave and evaporates the water, this water can no longer hold all the limestone it has dissolved and it releases part of it. Small drops of water emerging from the lime rock on cave walls are evaporated and calcite and other rock minerals are deposited along these walls. Where these drops cascade along the walls a continuous elongated ridge is deposited. If the water oozes out in an extremely fine coating of water, the entire ceiling, walls and floor may be paved with calcite. These deposits combine a rather even and general flow of water and possible intergrowth of the stalactites to make the thickened deposit. The ground water issued more rapidly and was concentrated at one point to make the long tubular deposits, the tube being made by rapid evaporation along the outer margins of the drops of water as they hang on the stalactite before the large part of the water falls to the floor. These deposits combine a rather even and general flow of water and possible intergrowth of the stalactites to make the thickened deposit. The ground water issued more rapidly and was concentrated at one point to make the long tubular deposits, the tube being made by rapid evaporation along the outer margins of the drops of water as they hang on the stalactite before the large part of the water falls to the floor. Where individual drops collect on the cave ceilings, a thin deposit may be formed on the ceiling after which the remaining water may drop to the cave floor where more calcite is deposited. Continuous dripping results in paired deposits extending down from the ceiling and up from the floor. The deposit on the floor is commonly thicker and more columnar, whereas that on the ceiling is thin and tapering much like an icicle. Those hanging from the ceiling are called stalactites and those on the floor are stalagmites. Where these two deposits are joined they are known as a column. These cave formations are all composed of the mineral calcite, which forms all lime rock. If you will notice in the cave this mineral is crystalline, and it is remarkable that as calcite crystallizes from the many individual drops of water it is arranged always in a particular pattern. These crystal faces reflect light and form the many unusual and beautiful arrangements which you will see in a visit to the caves. |
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