CHARTING CAPITOL GEOLOGY: TRENDS IN STONE TYPE, AND GEOGRAPHIC ORIGIN OF STONE, USED FOR STATE CAPITOLS

Capitols, being seats of government, are the most prestigious public buildings in the 50 states. Fittingly, most (n = 43) current capitols have exteriors made of stone or exteriors which utilize a major amount of stone, the most prestigious building material. Seven current capitols are faced with other materials (wood, stucco, concrete, and brick). Limestone (n = 19) is the most used stone for state capitols, followed by granite and other igneous stones (n = 13), sandstone (n = 7), and marble (n = 4).

Most, but not all, limestone capitols are located in states between the Appalachians and the Rockies. Salem Limestone (Indiana limestone) is the most used limestone, used for exteriors of the capitols of Alaska, Georgia, Indiana, Kentucky, Mississippi, New Jersey, Oklahoma, North Dakota, South Dakota, Tennessee, and West Virginia. Capitols using igneous rocks are located in states which are at least in part in igneous provinces (although the particular rock used may or may not be from that state). Sandstone use is local (with the exception of Michigan which uses Berea Sandstone from nearby Ohio). Marble use, though limited, is not based on local sources.

Trends in the use of stone for these buildings can be examined using seriation curves to plot stone used over time (using the date of completion of the entire or the major part of the capitol, the latter a judgment call due to the complexities of some capitol construction projects). These curves show a step-wise progression of first use of material for current capitols, beginning with wood, then granite, limestone, sandstone, and, finally marble. The choice of stone or other material used for these capitols was based on various factors. Depending on the capitol, these included availability, workability, desire for local material, cost, quality, experience with stone used for previous capitol or other buildings, and perceptions of attractiveness and durability. Granite was the dominant stone between 1800 and 1850 but its use decreased in proportion to the use of limestone between 1850 and 1950. Stone diversity was highest between 1825 and 1925, when most current capitols were constructed.