Your class will walk roughly one mile on the Adventure Tour, which lasts one hour. Your guide will stop the group roughly thirteen times on your trek through the cave in order to explain what can be seen and what we believe took place here prior to the cave’s discovery in 1963.
The tour begins in the pre-call room of the main building. Your guide will greet you and discuss the rules with your class before heading down into the cave. Please make sure everyone has used the restroom and that their shoes are tied!
As your class moves through the cave, the guide will be turning the lights in front of you on and the lights behind you off. This is partially to give the bats as natural a habitat as possible, but is also for communication purposes. When a guide comes to a room and the light is off, she has a better idea of where the guide in front of her is. If she comes to a room and the light is on, she will flash them once to let the other guide know that she is entering. Occasionally the lights will flash on your class as well; explaining this beforehand helps prevent the students from getting too excited when it happens.
Ground water drips through the rock above our heads. As it interacts with decaying plant and animal matter, it picks up carbon dioxide (CO2). The result is a very weak acid called carbonic acid (H2CO3). (Acid rain is the very same solution, only it picks up its CO2 in the air.)
As this acid makes its way through limestone, it brings the mineral calcite (CaCO3) along with it. It is the pressure of the rock on this calcium bicarbonate solution that keeps it all together. When this drop of water, carbon dioxide, and calcite is no longer under pressure; say, when it reaches a void in the rock such as a cave, the solution is no longer stable, and the carbon dioxide evaporates. Since the drop of water is no longer acidic, it does not have the ability to hold on to the calcite. The calcite is deposited on the nearest surface, and the location of this surface is what determines the name of the formation that will eventually grow there.
Types of formations:
- Soda straws are hollow, just like a straw
- Stalactites hang tight to the ceiling
- Stalagmites might reach the ceiling someday
- Columns are when stalactites and stalagmites grow together
- Flow stones form over walls, floors, boulders, and other formations
A new type of formation-drapery. Drapery forms along an inclined plane. As the water slides down the slanted ceiling or wall, it leaves a streak of calcite behind it. This piece of cave drapery has grown large enough that the calcite has cemented it with the stalagmite growing beneath it, making it a drapery column.
Roughly 100 million years ago, this part of Texas was covered by a shallow sea. Aquatic life forms would sink to the bottom of the water once they died. Their shells were made up of CaCO3 (calcite). As layer upon layer of shells and sediment built up on the sea floor, the pressure of the water and sediment above compacted them to form limestone. The ceiling here is made up of fossilized sea coral, and we can see callianassa shrimp burrow fossils near the center. These are trace fossils-indirect evidence that denotes animal behavior rather than the animals themselves.
Your guide may want to do total darkness in this room. It is very important that everyone stands still and quiet when the lights go out. With the removal of one of your senses it is easy to become disoriented, and your guide needs to be able to hear if there is a problem. Some guides prefer to do total darkness in the last room on the tour.
They expanded one of the 6-inch diameter holes to a diameter of 24-inches and they lowered Mr. Jack Bigham down on the kelly of the auger rig. He was the first human being to enter Inner Space Cavern. The “Discovery Hole” as we call it was drilled right above a petrified pile of bat guano! Anyone coming and going had to trek through the pile for the first three months of exploration, after which the hole was sealed so construction of I-35 could progress. It was decided that the 33.5 feet of rock above Discovery Room met Highway Department standards, so they did not change their plans for construction. Interstate Highway 35 runs right above this room.
The Flowing Stone of Time is one of the older flowstones on the commercial pathway. The University of Texas took a core sample from the formation in order to date it and determined that this formation is at least 27,000 years old. The funny-shaped rim pool at the bottom is 3 feet deep and can hold up to 125 gallons of water. The water in the cave is filtered by the rock that it trickles through so is 98% pure. It takes roughly 3 days for water from the surface to reach the cave.
We can tell from the large size of the scallops that the water was moving through this section of the cave rather slowly. (The slower the water, the lesser the energy on its surface, which leads to larger wavelengths and larger scallops.) We believe the reason we see scallops here and not in other rooms is because the adjacent sink hole allowed water into the cave at a quicker rate than could seep through into the cave at other locations.
Between these two events, fauna from the last glacial maximum used this sinkhole to access the cave. The humidity of the cave encouraged vegetative growth around the sinkhole, which would attract animals to graze there. Most probably fell 50 feet from the rim to the cave floor and did not survive, but some paleontologists speculate that saber-toothed cats may have used the cave as a den to raise its young. The bones of at least 44 different species of animal have been found in the cave so far, 11 of which are extinct.
All of the animals represented here are animals whose fossils we found in the cave. Starting on the far left we have:
Giant Ground Sloth - Relative of the three toed sloth currently living in the rainforests of South and Central America. They walked on their knuckles and grew to the size of a suburban.
Glyptodont sp. – Relative of the armadillo. They were herbivores and grew to the size of a VW bug.
Equus sp. – Similar to the horse, but smaller. Modern horses are not native to North America, but were brought over by the Spanish.
Black-Tailed Prairie Dog – This is the only species on the wall that is not extinct. Fossil evidence shows that they have remained virtually unchanged for 25,000 years.
Saber-toothed Cat – One tooth is all we found of this animal. Hair does not fossilize, so we do not know if they had stripes or not; therefore, we do not call them tigers.
Peccary – Relative of the Javelina. We found their bones most frequently in the cave.
Camelops sp. – Slightly smaller than the modern camel. Cartilage rarely fossilizes, so we do not know how many humps they had. Camel’s humps are used for storing water. Their environment was much lusher here than where they live today, so they may not have had a hump at all.
Columbian Mammoth – Larger relative of the Wooly Mammoth. Stood up to 14 feet at the shoulder and weighed from 8-10 tons. The largest tusk found to date is 16 feet long. These animals were herbivores.
There is a display case located next to the mammoth containing some of the fossils we found in the cave. The majority of the bones went to Southern Methodist University and the University of Texas for study.
The ladder was used for maintenance and the removal of fossils while the cave was being commercialized. The hole was originally drilled to improve the air quality of the back rooms. There is a little red shed sitting on top of this hole with “Inner Space” painted on it located on the east side of the highway. It is a good landmark if you want to see just how far we travelled underground.
The other side of the debris cone we passed earlier can be seen at the far end of this room. This sinkhole is approximately the size of a football field and we have walked to the opposite side of it here.
If your guide has a chance to show you total darkness here, it helps to have your students sit on the brick wall surrounding the room. Be sure that you are not sitting on a stalagmite! Again, please help us with keeping your students calm and quiet.
This is the last room on the tour. We will walk all the way back to the entrance, stopping occasionally so the guide can turn off the lights and make sure the group stays together. The walk back is a great time to ask questions!