Surface erosion continued to tear away at the mountains. Streams cut their valleys deeper. In response, the water table gradually sank below the level of the caverns and they, in turn, were drained. Air entered the rooms. The basic excavation process was completed except for a few minor changes: In some places, vadose water continued to dissolve away portions of the cave ceilings into dome shapes. In other rooms previously drained, water re-flooded certain portions during wet cycles. And some rooms were filled with clay and gravel brought in from the surface, then washed clean again in later stages. Most important is the entrance of air, which ushered in the second major stage in cave formation. The unadorned grottoes were now to be decorated. Nature, through the process of _deposition_, next created the eerie beauty which delights today’s cave visitors. In fact the process continues even now, for Oregon Caves are “live” caves, meaning they are still being decorated by natural deposition. The weak carbonic acid in vadose water kept eating away the roof marble above the caves. Reaching the caverns, drops of vadose water evaporated into the air and left their load of calcium carbonate as thin layers of solid mineral. The amount left by each drop was infinitesimal, yet millions of drops eventually left thick deposits coated on the walls, ceilings and floors of the cave. The crusty white deposits in the Beehive Room are fine examples of deposition by _evaporation_. They were left there in much the same way as the coating in the bottom of a teakettle or steam iron. However, evaporation is important only near the surface. Deeper inside Oregon Caves the relative humidity averages 98 percent. Evaporation here is almost non-existent. Instead, _loss of carbon dioxide_ becomes the chief agent of deposition. We have learned that vadose water contains 25 to 90 times the normal amount of carbon dioxide found in the atmosphere. Much of it, of course, unites with calcium carbonate to form calcium bicarbonate solution. When this mineralized water reaches the caverns, large quantities of carbon dioxide are able to escape into the air due to the difference in carbon dioxide amounts in the water and air. The chemical balance is upset. For each molecule of escaping carbon dioxide, an equivalent molecule of solid mineral is deposited (see illustrations page 10).