So far we have discussed cave features—_speleothems_—created by deposition of mineral from the solid to liquid, and back to solid state. But certain objects in the caves are simply what remains of a piece of marble after some of it is dissolved away. These are _speleogens_, cave features created by the dissolving of mineral (see illustration page 24 ). They can be striking, but primarily it is the _speleothems_ which make Oregon Caves a thing of wonder and beauty. The zenith of such spectacular development as seen at Paradise Lost leaves little doubt of this. We have followed the mineral calcium carbonate through many forms: from sea creatures to ocean mud, to limestone and then marble, next to a liquid solution called calcium bicarbonate, and lastly as calcite crystals in cave formations. The size, shape and variety of cave deposits are determined by many factors which seem to prevent any two being exactly alike. Changes in temperature, relative humidity, available carbon dioxide, amounts of vadose water, air circulation, surface tension, permeability of roof rock, vegetation above the cave, bacteria action, and the amount and kind of impurities in vadose water may all combine to vary the nature of cave formations. [Illustration: Detail in Paradise Lost] [Illustration: Speleogen above River Styx] _The Cave’s Age_ The many variables make it difficult to accurately estimate the age of cave deposits. We have no way of determining past conditions which have influenced the rate of development. Oh, we know the formations are many thousands of years old, beyond that we can only guess. Some crude examples of known age are the tiny, one-half-inch stalactites formed in the exit tunnel since it was completed some 38 years ago (see illustration below). Bathed in warm, dry air from the outside, they have probably developed much faster than those inside the main cave. Other active formations deep in the cave show very little visible depositing over names written on them by early explorers in the 1880’s. So the true secret of the age of the formations must rest with the cave itself. Perhaps this is best. [Illustration: Stalactites formed since exit tunnel was completed in 1933] _Other Cave Features_ An obvious feature you may see in Neptune’s Grotto is the brown lacework on the walls. They are lines of clay. Molecular attraction causes the clay particles to cling together into what we call _clay worms_. (See illustrations on page 27). Where does the clay come from? Some of it may be washed in from the ground above. The rest of it is the remnant of marble solution. Oregon Caves marble is 93 percent calcium carbonate. The remaining 7 percent is non-soluble clay and remains in the cave after the calcium carbonate is carried away in fluid state. Clay worms are temporary features; vadose water or the touch of a careless hand can easily remove them.