Finding a natural connection between Halloween and the study of geology is a challenge, but one eery location where the two fit perfectly together is a graveyard. For centuries, humans have sought out specific types of rocks to be used as gravestones. Likewise, the locations of graveyards are picked taking local geology into consideration.
Rock Types Used in Tombstones
The types of rocks used in traditional gravestones has changed over the years. In America, access to different rock types was the main factor in picking a rock for a tombstone, followed by the rock's ability to withstand weathering. Like rocks themselves, the types of rocks used have changed over time, reflecting the rock availability in a particular area, or the amount of effort and technology that was needed to extract those rocks.
The different rock types used in gravestones, and when and where they were used, are as follows:
- Shale (metamorphic rock) was used from 1650 to 1900. From 1660 to 1800, the center of the gravestone commercial industry was Boston, MA, where slate was readily available.
- Sandstone (sedimentary rock) was used from 1650 to 1890. This type of gravestone was most commonly used during this time in the Connecticut Valley, where sandstone formations were plentiful. The sandstone gravestones were also shipped via railroad to many other regions througout the Eastern U.S.
- Marble (metamorphosed limestone) and limestone (sedimentary rock) were used from 1780 to 1930. Popular for its bright white color, marble and limestone can be found in many places throughout the U.S., including Georgia, Vermont and Colorado. However, carbonate rocks, such as limestone and marble, are susceptible to erosion from acid rain, which is common in more polluted areas.
- Granite (igneous rock) is currenlty the popular choice for gravestones and some cemeteries even phohibit gravestones or gravemarkers that are not made of granite. The use of granite began in 1860 and quickly became the gravestone of choice for its sturdiness and beauty.
Geologic Factors for Picking a Gravesite
When picking the location of a gravesite, or a graveyard, the local geology needs to be taken into account. For example, the depth of the water table, the hardness of the ground, and the likelihood of flooding. The goal is to pick an area that has a ground soft enough to dig deep holes, but not so soft that it will easily erode. Even for hard ground that does not erode quickly, a flood bringing fast moving water can displace several feet of dirt, unearthing buried remains.
Geology activities that can be done in the field at a local graveyard include identifying the rock types used in the various gravestones, and mapping a gravesite in relation to local water features that could potentially become a hazard. Be careful to get permission from the appropriate official or graveyard attendant to plan a field trip. The last thing one wants to do is disturb the dead!
Sources:
" History of American Gravestones ," ArtisanMemorials.com, accessed October 25, 2011.
Guertin, L., 2008, "Cemetery Investigations Tombstone Weathering," psu.edu, accessd October 25, 2011.
Hannibal, J.T., 2007, "Teaching with Tombstones: Geology at the Cemetary," in Shaffer, N.R., and DeChurch, D.A., eds., Proceedings of the 40th Forum on Geology of Industrial Minerals, May 2-7, 2004, Bloomington, Indiana: Indiana Geological Survey Occassional Paper 67, p. 82-88.
Alexandra Matiella Novak - With a PhD in Geology and expertise in science education, Alexandra is passionate about increasing the public's Earth science literacy.
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