Carthage “Marble” in Fort Smith
The Frisco Train Depot at the Fort Smith National Historic Site
Opened in 1903, the Frisco Depot at Fort Smith was an impressive structure said to represent the status of the city and its residents. Built in the Greek style, tall iconic columns originally supported the portico on the north side of the building but were removed in the mid 20th century to make room for bridge expansion. The depot provided passenger and freight service until 1912 when the Frisco line trains began operating out of the newly built Fort Smith Union Depot on Rogers Avenue. Service continued there until 1948 when Frisco switched back to the Garrison depot for its last few decades of service before closing its depot doors at the Garrison Avenue location for good. The years following the Frisco line's departure saw many changes in usage for the depot building including restaurants and offices. In 2003, the National Park Service purchased the historic depot and has been working on normal preservation and maintenance improvements.
The Frisco Train Depot building consists of limestone blocks. The smooth rectangular cut stone creates a surface style of blocks closely fitted together with very thin joints of mortar called Ashlar masonry. The stone blocks are built from Carthage, Missouri quarried Limestone.
The limestone deposits from Carthage, Mo belong to the Burlington group of the Mississippian Carboniferous strata. They are composed of the remains of crinoids and other shell-fish of the Silurian and Carboniferous epochs. The stone has a crushing strength three times that of the Bedford limestone making it more difficult to cut and dress.
An early report of the Missouri Bureau of Geology and Mines reads that “in uniformity of color, this is the peer of limestones. The calcite grains are closely interlocked, giving the stone strength and durability.” Because of this, Limestone from this area was often called Carthage “Marble” although it is not technically a metamorphic rock, and therefore not scientifically marble.
Geologic Origin of Limestone: Most limestone forms in warm, shallow-marine environments through the precipitation of calcium carbonate (CaCO3) out of seawater. The precipitate settles to the seafloor and accumulates as a blanket of carbonate mud. The calcareous remains of marine organisms, including the tests and shells of invertebrate animals and the remains of calcareous algae accumulate along with the carbonate mud and become incorporated in it. Often, sand-size particles of calcium carbonate such as ooids and the fecal pellets of bottom-dwelling, mud-eating invertebrates are also added to the mix. The result is carbonate sediment that contains an assortment of different-size particles of various local origins. The sediment is progressively buried and compacted by the accumulation of more calcium carbonatesediment. Under certain conditions, magnesium ions in seawater may replace some of the calcium in the sediment, resulting in sediment than is dolomitic. When the sediment becomes buried deep enough and is sufficiently compacted, it lithifies into calcitic limestone or dolomitic limestone rock. Limestone that contains visible fossil remains is called fossiliferous limestone.
Stone from the quarries in Carthage generally contain brachiopod, twig-like bryozoans and other fossils and may or may not be stylolitic. Most stylolites are bedding-parallel, and thus most likely formed due to the weight of the overlying rock. Calcite, the dominant mineral, goes into solution under pressure, and insoluble material, like organic matter and clay, accumulates along the dissolution surface, producing a dark, wiggly line.
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- What color is the limestone at the Frisco Train Depot?
- Do you see any fossils in the limestone?
- Do you see any stylolites in the limestone?