From the Association of Gravestone Studies [Issue 71 March 2009] which I receive as a member is this interesting article [pdf].
"Hannibal, J. T. 2007. Teaching with tombstones: geology at the cemetery, p. 82-88. In N. R. Shaffer and D. A. DeChurch (eds.), Proceedings of the 40th Forum on the Geology of Industrial Minerals, May 2-7, 2004, Bloomington, Indiana, Indiana Geological Survey Occasional Paper 67."