Questions 31-40 refer to the following passage.

    The most familiar speleothems (from the Greek word spelaion for the cave and thema for deposit), the decorative dripstone features found in caves, are stalactites and stalagmites. Stalactites hang downward from the ceiling of the cave and are formed as drop after drop of water slowly trickles through crack on the cave roof. Stalagmites grow upward from the floor of the cave, generally as a result of water dripping from an overhead stalactite. A column forms when a stalactite and a stalagmite grow until they join. A “curtain” or “drapery” begins to form on an inclined ceiling when drops of water trickle along a slope.

    Natural openings on the surface that lead to caves are called sinkholes. or swallow holes. Streams sometimes disappear down these holes and flow through the cavern. Rivers may flow from one mountain to another through a series of caves . Some caverns have sinkholes in their floors. Water often builds up a rim of dripstone around the edge of the hole. Dripping water often contains dissolved minerals as well as acid. These minerals too will be deposited; and they may give rich coloring to the deposits. If minerals in the water change, layers of different colors may be formed.

Stalagmites are formed by ...