Cave deposits in Joaquin Miller’s Chapel
Drapery in Ghost Room
Cave deposits are collectively termed speleothems. Their variety is infinite: Those left by dripping water are called dripstone, and take on two basic forms—if they hang down from the ceiling they are called Stalactites, if they grow up from the floor they are stalagmites. The two may join together to form a column. Where the water drips rapidly and the loss of carbon dioxide is slow, stalagmite growth is favored because little deposition can take place on the ceiling. If the drip rate is slow and loss of carbon dioxide is rapid, stalactite formation is favored.
Formations on [page 16]
Contrasted with dripstone is flowstone—smooth layered deposits left along walls and floors by flowing water. In Joaquin Miller’s Chapel, flowstone deposits are many inches thick. (See illustration on [page 16]). A close look at the structure of dripstone and flowstone reveals six-sided crystals called calcite, which is merely the crystalline form of calcium carbonate. (See illustration on [page 19]). Banded crystal layers in cave deposits are often called alabaster, or cave onyx. These can be easily seen at the “wishing post.”
Other shapes and forms accrue. Flowstone forming on backsloping walls tends to produce graceful sheets called drapery. (See illustration on [page 17]). Reddish bands may develop in drapery where iron oxide is imbedded with the calcite. Contrasted with the pure white layers of calcium carbonate, this gives the appearance of bacon. Good examples of “bacon” can be seen in the Ghost Room.
Most shapes and forms of dripstone and flowstone are occasionally duplicated by freezing water. Stalactites form on the edges of roofs, stalagmites form on the sidewalk beneath them, etc. But one of several cave formations which can’t be thus copied is the soda straw (see illustration [page 20]). Deposition begins as a ring of calcium carbonate around a water drop. The ring has the unique feature of being a single crystal. As more drops leave their deposits, the ringed crystals form one on the other to create a tube. The water continues to seep through the inside of the tube, eventually producing the fragile, crystalline pipe with the obvious name.
The diameter of a soda straw is apparently determined by the specific gravity and surface tension of water, for they are all nearly the same diameter, about one-quarter inch. In a cave in western Australia one soda straw has reached a length of 20 feet, 6 inches, yet is still only one-quarter inch in diameter. If the drip rate decreases, the tip of the soda straw may sometimes seal itself closed.