THE RISE AND FALL OF THE SENECA SANDSTONE INDUSTRY

Seneca sandstone was an important building material in the Washington DC area during the 19^th century. It is an arkosic, micaceous sandstone as indicated by micro-X-ray diffraction (XRD) analyses, which show that quartz, alkali feldspar, and muscovite predominate. Instrumental neutron activation analysis (INAA) measured about 5% Fe₂O₃, which accounts for the characteristic red color. Trace amounts of manganese (0.05 % MnO₂) may also affect the coloration. The formal name for Seneca sandstone is the Poolesville Member of the Manassas Formation. This occurs in the Culpepper Basin, which passes from Virginia into Maryland under the Potomac River. This formation is in turn a member of the Newark Supergroup, a series of Triassic sandstone basins that reach from North Carolina to Massachusetts. The Newark Basin in New Jersey, as well as quarries along the Connecticut River in Massachusetts, supplied much of the brownstone used in New York City buildings during the 19^th century. The Seneca quarries were located in Maryland near where Seneca and Bull Run Creeks enter the Potomac River about 40 km northwest of the District. It has been quarried since 1774, but the opening of the C&O Canal as far as Seneca, MD, in 1831 made possible the operation of the quarries on a large-scale commercial basis. The most prominent example of its use was for the Smithsonian Castle’s construction in 1847-1855. Its selection for this building involved one of the earliest applications of the sodium sulfate test for stone durability. The Castle’s design, by James Renwick, Jr., established the Romanesque Revival architectural style, which was popular during the Victorian era. Seneca sandstone was used extensively in public and private buildings during this period, but fell out of fashion by its end. Quarrying had mostly ceased by 1900 as good-quality stone became scarce, and the quarries were completely abandoned after severe flooding in 1924. Remains of the quarry, including the ruins of a stonecutting mill, can be visited in Seneca Creek State Park in Potomac, Maryland.