Bog iron formation in the Nassawango Watershed, Maryland

Abstract

Introduction Bog iron deposits occur at a number of localities in the Pocomoke River basin. The most extensive deposits are situated along Nassawango Creek northwest of Snow Hill, a town on the Pocomoke River. After the discovery of these deposits an iron furnace was built in 1830 on the west side of Nassawango Creek, five miles northwest of Snow Hill, at a location known as the Furnace. The furnace exclusively smelted bog iron obtained along Nassawango Creek for a mile or so north of the furnace site; iron was produced from 1830 to 1850 at a rate of approximately 700 tons per year. Smelting technology of that period used mollusc shells for lime flux and locally burned charcoal for fuel; they were unable to remove phosphorous and the iron was rendered brittle when cold ("cold short") because of the high phosphorous content inherited from the ore. For that reason, and because of the limited size of the deposits and the discovery of the much larger and higher quality ore deposits in other parts of the country, production ceased about 1850. The bog iron deposits have been forming throughout the Holocene and are still forming today. Singewald (1911) stated, that their chief interest today lies in the fact that the deposits are now forming and at such a rate as to be observable. "Deposits which were once exhausted are again workable after an interval of a few years" (for more on rate of formation of bog ore at different locations see Starkey, 1962 and Moore, 1910). In general, bog ores consist primarily of iron oxyhydroxides, commonly goethite (FeO(OH)). The ores in the Nassawango, in addition to goethite and other ferric oxyhydroxides, contain a significant amount of magnetite.