More common names for bog limestone are tufa and travertine. Geologically, these deposits are relatively young, forming sometime in the past 200 thousand years and they continue to form today. Tufa is a deposit of calcite (CaCO3) that forms where ground water rich in dissolved carbonates emerges at the surface as a natural spring. When carbonate rich water comes to the surface there is a drop in pressure that causes it to lose CO2 gas and become saturated with calcium carbonate, resulting in the precipitation of calcite. Fossils are the preserved remains of plants and animals that lived in the past. As tufa is forming plants and insects may be coated with calcite leaving behind their imprint as a fossil.
It is very rare to come across buildings made of bog limestone, much less a building the size of a church. Most likely this is because tufa deposits tend to be small and localized. Tufa is also less sturdy and harder to work than traditional building stones.
To log this cache you will need to take a close look at the rocks this church is made of and email the CO with answers to the following questions:
- Compare the rocks in the foundation to main part of the church, how are they different?
- Find and describe a fossil in the tufa. What type of plant or animal do you think it was?
- Where was the “bog limestone” quarried?
Congratulations to Upstate Brent the FTF