An interesting side effect of the loss of carbon dioxide is experienced by the cave visitor. Although cave air is constantly replenished by outside air through natural exchange, it has a rather high carbon dioxide content due to release of this gas by vadose waters. This partly explains the heavy breathing you find necessary inside the cave, because the nerve centers which control our breathing are stimulated by a high percentage of carbon dioxide in the air we breathe. It also explains the odd “peroxide” odor many people notice when they reach the exit. The odor is oxygen. We notice it because our senses have become adjusted to slightly lower oxygen percentages inside the cave. [Illustration: Cave deposits in Joaquin Miller’s Chapel] [Illustration: 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. [Illustration: 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.