Marble Ceiling
The Marble Ceiling has a smooth ceiling, showing a great example of the marble that makes up the majority of the Oregon Caves. Visible on this ceiling are lines of graphite and the weathering feature known as boxwork. On the walls, erosional features can be seen showing past stream flow.
Geology
Room Development
The dark lines seen in the marble of the Oregon Caves are graphite. These graphite lines were the result of an abundance of microbes in the Pacific Ocean, about 250 million years ago, as the limestone formed (Roth 12). Around the same time, at the Permian-Triassic boundary, the Earth experienced a mass extinction event, known as the Permian-Triassic Extinction. This event was especially devastating to marine life. Approximately 95% of ocean-dwelling species were wiped out, killing off most of the suspension feeders, carnivores and almost all reef dwellers (NASA). This allowed for an abundance of microbes to remain in the ocean, which later formed the bands of graphite (NASA; Roth 12).
Cave Formations
The ceiling contains calcite veins, which can be seen as thin lines sticking out slightly from the marble. When calcite veins intersect to create little “boxes”, as they do in this room, they are called boxwork. This formation is caused by mineral deposition in 
fractures and as the marble erodes away, this more resistant formation begins to project out of the ceiling (Bates and Jackson 83). This is due to the fact that calcite veins have coarser crystals than the marble.
Water Flow
The River Styx once flowed higher in this room, which created shelf-like erosional features called bevels. These can be seen on the side walls, and are about two feet high and deep, indicating past stream flow (Roth 13). These notches formed when sediment stopped the stream from cutting downwards. Instead, the stream carved into the passageway sides (Lundberg 320). Today, the stream flows below the trail but sediment deposits can still be seen along the walls (Roth 15).
Bates, Robert and Julia Jackson, ed. Glossary of Geology. Alexandria: American Geological Institute, 1987. 83.
Lundberg, Joyce. “Karren.” Encyclopedia of Caves. David Culver and William White, ed. Burlington: Elsevier Academic Press, 2005. 315-321.
Roth, John. “Interpretive Manual for the Monument’s Showcave”. Cave Junction: Oregon Caves National Monument, 2011. 12-15.
National Aeronautics and Space Administration. "The Great Dying." NASA Science: Science News. 2002. NASA. 06 July 2011 <http://science.nasa.gov/science-news/science-at-nasa/2002/28jan_extinction/>.