Gravestones (a.k.a. headstones / tombstones) in modern American cemeteries are usually made of "granite" - a term in the retail trade for any hard stone that will take a fine polish. Geologically, some are granites and some are not. In the 1800s, many gravestones were made of marble, a crystalline-textured metamorphic rock composed of calcite (calcium carbonate, CaCO3). Rainwater is naturally acidic (slightly), with carbonic acid - H2CO3. Over time, marble will slowly dissolve in rainwater. Older marble gravestones typically have poorly legible carvings.
The old marble tablet gravestone seen here was originally oriented upright. Differential loading of the soil by the weight of the gravestone over time has tilted it. Creep may have played a role as well, even though this is not a steep hillside.
"Creep" is a geologic term for slow migration of rock or soil due to gravity. It can be observed on some steep hillsides where trees have non-vertical trunks. Some anthropogenic constructs can be noticeably affected by creep - for example, power line poles, telephone poles, and gravestones.
Locality: Cedar Hill Cemetery, Newark, Licking County, east-central Ohio, USA
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