They are typified by being highly eroded, with conspicuous deep vertical fissures and narrow ledges. This carbonic acid gradually dissolves limestone thereby enlarging the fissures. As the deformity worsens, pits, nodules, fissures, lobulations, and pedunculation contort the nose. Surface water containing natural carbonic acid moves down into small fissures in limestone. Emeralds tend to have numerous inclusions and surface-breaking fissures. Some of the fissures were lined with calcite, and rubble filled others. Repeated attacks may result in fissures and skin thickening. Sometimes there is a large central furrow, with smaller fissures branching perpendicularly. The largest fissures were actually caves large enough to enter. The fossils are found in partially infilled paleokarst fissures across Monte Gargano. The cerebellum is composed of several dividing fissures and lobes. During February 1921, white steam erupted from eastern fissures on the volcano. Each lung is divided into lobes by the infoldings of the pleura as fissures. Olms are gregarious, and usually aggregate either under stones or in fissures. Emeralds containing natural fissures are sometimes filled with wax or oil to disguise them.