We are having some excavation done and these rocks keep surfacing. They are 16 inches across or more, with some being nearly a yard wide. They have strange holes and appear to have interlocking parts. There is a coal mine under our property, and
fire clay in the area of these rocks.
I noticed this was your very first post - so, Welcome Aboard Emie! You didn't list your state (or country) in your profile. So, you might consider jumping over to Sub-Forums: Select Your Area.... and selecting location information (i.e., clubs, hunts, finds, legends, maps, etc.) directly related to your state (or country). You might also consider adding your state (or country) to your displayed profile (SETTINGS -> EDIT PROFILE) so if you ask a question, etc. - people may have more success helping you (your location may help, etc.)...